FIELD OF THE INVENTION

The invention relates to a light generating system, such as for use in a projector system, especially an LCD based projector. The invention also relates to such projector system.

BACKGROUND OF THE INVENTION

Luminescent rods are known in the art. W02006/054203, for instance, describes a light emitting device comprising at least one LED which emits light in the wavelength range of >220 nm to <550 nm and at least one conversion structure placed towards the at least one LED without optical contact, which converts at least partly the light from the at least one LED to light in the wavelength range of >300 nm to <1000 nm, characterized in that the at least one conversion structure has a refractive index n of >1.5 and <3 and the ratio A:E is >2:1 and <50000:1, where A and E are defined as follows: the at least one conversion structure comprises at least one entrance surface, where light emitted by the at least one LED can enter the conversion structure and at least one exit surface, where light can exit the at least one conversion structure, each of the at least one entrance surfaces having an entrance surface area, the entrance surface area(s) being numbered Ai ... A _n and each of the at least one exit surface(s) having an exit surface area, the exit surface area(s) being numbered Ei ... E _n and the sum of each of the at least one entrance surface(s) area(s) A being A = Ai +A ₂ ... + A _n and the sum of each of the at least one exit surface(s) area(s) E being E = Ei +E ₂ ... +E _n .

SUMMARY OF THE INVENTION

High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection, and (fluorescence) microscopy and endoscopy etc.. For this purpose, it is possible to make use of so-called light

concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. A rod of such a transparent luminescent material can be illuminated by LEDs to produce longer wavelengths within the rod. Converted light which will stay in the luminescent material, such as a (trivalent cerium) doped garnet, in the waveguide mode and can then be extracted from one of the (smaller) surfaces leading to an intensity gain.

In embodiments, the light concentrator may comprise a rectangular bar (rod) of a (transparent) phosphor doped, high refractive index garnet, capable to convert blue light into green or yellow light and to collect this green or yellow light in a small etendue output beam. The rectangular bar may have six surfaces, four large surfaces over the length of the bar forming the four side walls, and two smaller surfaces at the end of the bar, with one of these smaller surfaces forming the“nose” where the desired light is extracted.

Under e.g. blue light radiation, the blue light excites the phosphor, after the phosphor start to emit green light in all directions, assuming some cerium comprising garnet applications. Since the phosphor is embedded in - in general - a high refractive index bar, a main part of the converted (green) light is trapped into the high refractive index bar and wave guided e.g. via Total Internal Reflection (TIR) to the nose of the bar where the (green) light may leave the bar. The amount of (green) light generated is proportional to the amount of blue light pumped into the bar. The longer the bar, the more blue LED’s can be applied to pump phosphor material in the bar and the number of blue LED’s to increase the brightness of the (green) light leaving at the nose of the bar can be used. The phosphor converted light, however, can be split into two parts.

A first part consists of first types of light rays that will hit the side walls of the bar under angles larger than the critical angle of reflection. These first light rays are trapped in the high refractive index bar and will traverse to the nose of the bar where it may leave as desired light of the system. In general, at least part of the luminescent material light may escape from the radiation exit face directly (without total internal reflection).

A high lumen density (HLD) system may comprise a ceramic rod, where blue light is converted to create a high intensity source for theatre lighting, beamers etc. For optical efficiency, i.e. LED alignment with rod, thermal performance, i.e. cooling by conductive heat spreading, and mechanical fixation inside (e.g.) a projector module, the rod may be clamped by metal rod holders.

The rod may be configured in a rod holder. A system may e.g. be based on irradiation of the rod with light sources from two sides of the rod. Such rod-holder may e.g. be generated with die-casting.

HLD lamps are relative new semiconductor light sources based on a blue LED pump source and a luminescent rod. These HLD sources can replace current UHP lamps in all kind of LCD and DLP beamers. The current HLD lamps have an etendue of about 16.5 mm ² *sr whereas the UHP lamps have Etendue of about 8 mm ² *sr. The lower the Etendue of the source the easier it is to collect the light and the smaller the optics could be till they are limited by other parameters like tolerances and too large power per mm ² . HLD may outperform all specific beamer LED sources. Semiconductor lasers may outperform HLD but are very expensive and have their own specific problems such as impaired picture quality, safety and artefacts. A larger etendue of the standard HLD system w.r.t. UHP systems may especially be a problem for smaller LCD panel engines with panel sizes of 0.65” for which etendue sources of below 13 mm ² *sr are desirable. Etendue may be decreased by applying luminescent rods with smaller cross-sections. However, then there may be less illumination area on the luminescent rod available for the blue pump source, thus hampering or even limiting the amount of blue pump light that can be coupled into the luminescent rod, thus limiting the maximum achievable optical output of the HLD source or reducing its overall efficiency. Lurther, for LCD projectors polarized light is to be used. In prior art system, polarization may be obtained at the cost of efficiency.

Hence, it is an aspect of the invention to provide an alternative light generating system comprising a luminescent concentrator, which preferably further at least partly obviates one or more of above-described drawbacks and/or which may have a relatively higher efficiency. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.

Herein, in embodiments a different layout of the LCD engine used in the LCD projector is proposed, such as in some specific embodiments the single-sided HLD source could be much easier implemented in LCD engines. With presently proposed embodiments etendues <16.5 are possible without too much loss in blue source pump area and hence total output. Lurthermore, thermal management of the single-sided HLD module, especially that of the luminescent rod, may also be easier resulting in lower luminescent rod temperatures and by which the system becomes more efficient and by this partly compensates less blue pump source area. Together with the new proposed LCD engine architecture an efficient, cost effective HLD source with a lower light source etendue and sufficient output power may be obtained.

In an aspect the invention provides a light generating system (“system”) comprising a light generating device and beam splitter, especially a polarizing beam splitter (or“polarization beam splitter”), wherein the light generating device comprises (i) a plurality of light sources configured to provide light source light; (ii) an elongated luminescent body (“body”,“luminescent body”,“elongated body”,“concentrator”,“light transmissive bod”) comprising one or more side faces, the elongated luminescent body comprising a radiation input face, wherein the radiation input face is configured in a light receiving relationship with the plurality of light sources, wherein the elongated luminescent body comprises luminescent material configured to convert at least part of light source light (received at the radiation input face) into luminescent material light; and (iii) a radiation exit window for emission of the luminescent material light of the light generating device, wherein the radiation exit window has a first height (Hl) and a first width (Wl), defining a first aspect ratio

ARl=Wl/Hl; and wherein the beam splitter, especially a lateral displacement polarizing beam splitter, is configured in a light receiving relationship with the radiation exit window (of the light generating device), wherein in embodiments the lateral displacement of the lateral displacement polarizing beam splitter is configured in a direction parallel to the first height (Hl) of the radiation exit window.

With such light generating system, a relatively small etendue may be obtained, like smaller than 15 sr*m ² , or even smaller than 14 sr*m ² , like even smaller than 13 sr*m ² , such as yet even smaller than 12 sr*m ² , and even values below 10 sr*m ² may be achievable with a high intensity light source, and which may be suitable as light source in e.g. LCD projection. However, even though the etendue is reduced, there may still be enough area to pump the luminescent body with the light of the light sources. The term“etendue” (or “etendue”) refers to a property of light in an optical system, which characterizes how "spread out" the light is in area and angle. It corresponds to the beam parameter product (BPP) in Gaussian optics. From the source point of view, it is the product of the area of the source and the solid angle that the system's entrance pupil subtends as seen from the source. With the present invention, system efficiencies can be obtained that are comparable or even better than state of the art system efficiencies. To the best of our knowledge, existing light sources for projectors have an aspect ratio of about 1 (UHP), and sometimes up to about 1.7.

As indicated above, the invention provides a light generating system comprising (i) a plurality of light sources, (ii) an elongated luminescent body, and especially (iii) a beam splitter, especially a lateral displacement polarizing beam splitter.

The plurality of light sources are configured to provide light source light. At least part of the light source light is absorbed by the luminescent body and converted into luminescent material light. To this end, luminescent body comprises a radiation input face, wherein the radiation input face is configured in a light receiving relationship with the plurality of light sources. Hence, the light sources and the luminescent body are configured such that during operation at least part of the light source light enters the luminescent body (and is converted thereby). Further, as indicated above the elongated luminescent body comprises luminescent material configured to convert at least part of light source light (received at the radiation input face) into luminescent material light. The luminescent material light may escape from the luminescent body. Especially, for instance by using one or more reflectors at one or more sides and/or faces of the luminescent body, the luminescent material light may especially escape from the luminescent body at one face. This face, here below also indicated as second face, may comprise a radiation exit window. In embodiments, the second face is the radiation exit window. Further, the elongated luminescent body comprising one or more side faces. The number of side faces is herein also indicated with reference N. The elongated luminescent body may especially comprising four side faces, providing a rectangular cross-section (perpendicular to an axis of elongated of the elongated body). The elongated luminescent body may in embodiments comprise a garnet type A3B5O12 luminescent material comprising trivalent cerium.

As will be further elucidated below, the elongated luminescent body may have a length, a width, and a height. The elongated luminescent body may include a radiation exit window. This radiation exit window, which may especially be an end face, may have a first height and a first width. In many embodiments, as also depicted herein in a number of drawings, the first height of the radiation exit window and the first width of the radiation exit window are (essentially) identical to the height and width of the elongated luminescent body, respectively. Hence, the aspect ratio of the width and height may essentially be the same as the first aspect ratio of the first width and height.

The generally rod shaped or bar shaped elongated luminescent body can have any cross-sectional shape, but in embodiments the cross section has the shape of a square, rectangle, round, oval, triangle, pentagon, or hexagon. Generally, the elongated luminescent bodies are cuboid. Hence, in some instances (see also above) the term“width” may also refer to diameter, such as in the case of an elongated luminescent body having a round cross section. Hence, in embodiments the elongated luminescent body further has a width (W) and a height (H), with especially L>W and L>H. Especially, W > H, more especially W > 2*H, even more especially W > 3*H. Especially, the first face and the second face define the length, i.e. the distance between these faces is the length of the elongated luminescent body. These faces may especially be arranged parallel. Further, in a specific embodiment the length (L) is at least 2 cm, such as 4-20 cm. In many embodiments, downstream of the elongated luminescent body, a collimator may be configured. This collimator may be in optical contact with the elongated luminescent body, such as in physical contact. In other embodiments, the collimator may form, together with the elongated luminescent body, a monolithic body. In such

embodiments, wherein a collimator is available, the radiation exit window of the collimator is of relevance, defining the radiation exit window of the light generating device. In such embodiments, the collimator may have a radiation exit window having a first height and a first width. Especially, the aspect ratio of the width and height may essentially be the same as the first aspect ratio of the first width and height. Hence, the radiation exit window of the collimator may essentially have the same aspect ratio as the elongated luminescent body. Hence, in embodiments the light generating system further comprises a collimator configured downstream of the elongated luminescent body, wherein the collimator comprises the radiation exit window.

As indicated above, in specific embodiments the radiation exit window has a first height (Hl) and a first width (Wl), defining a first aspect ratio ARl=Wl/Hl. Especially, in such embodiments the elongated luminescent body has a rectangular cross-section. In embodiments, the first aspect ratio is especially larger than 4:3.

The term“light generating device” especially refers to the combination of the elongated luminescent body and light sources, optionally in combination with one or more reflectors (see also below), and/or optionally in combination with a collimator, such as a compound parabolic concentrator or similar concentrator.

Embodiments of the light sources and the elongated body are also further elucidated below.

As indicated above, the system may further comprise a beam splitter, especially a polarizing beam splitter (PBS)), especially a lateral displacement polarizing beam splitter configured in a light receiving relationship with the radiation exit window of the elongated luminescent body (or the collimator). Especially, a lateral displacement polarizing beam splitter produces two parallel output beams which are separated by a lateral displacement. To this end, rhomboid prisms may be applied. The displacement is especially determined by the size of rhomboid prism, and may e.g. be in the order of about 2-20 mm, such as 2-15 mm. In embodiments, the lateral displacement polarizing beam splitter comprises one or two rhomboid prisms cemented to a right angle prism, and one or more (halve) wave plates to manage the polarization state of the output beams. The beam splitter may also be (indicated as) a polarization conversion system (PCS), such as described by Jihwan Kin et al., in APPLIED OPTICS / Vol. 51, No. 20 / 10 July 2012, which is herein incorporated by reference.

Hence, especially the lateral displacement polarizing beam splitter may be configured to convert an unpolarized (input) beam of light into two output beams of light having the same polarization, such as the s polarization or the p polarization. One of the output beams is laterally displace relative to the other of the beams. With the lateral displacement polarizing beam splitter, about 50% is not lost, as in a conventional polarizing beam splitter, but the about 50% that has an undesired polarization is converted into light having the same polarization as the (directly) transmitted output beam of polarized light. Hence, for example when the P _s polarization is transmitted, the P _p polarization is reflected and by retarder 90° rotated, and can be used also as it is converted into P _s polarization.

Alternatively, the same may apply when the P _p polarization is desired (and not the P _s polarization).

As indicated above, in embodiments the lateral displacement of the lateral displacement polarizing beam splitter is configured in a direction parallel to the first height (Hl) of the radiation exit window. Hence, effectively the aspect ratio of the resulting beam of light, which are the two output beams of light (having essentially the same polarization) is reduced relative to the aspect ratio of the elongated waveguide, as the aspect ratio of the beam of light downstream of the lateral displacement polarizing beam splitter is

approximately (W1/(2*H 1 )).

Especially, in embodiments the lateral displacement polarizing beam splitter comprises an array of lateral displacement polarizing beam splitter elements.

Hence, with the present invention a light generating system is provided that is configured to provide polarized (light generating system) light.

For beam shaping, the light generating system may further comprise optics. One or more optics may be configured upstream of the lateral displacement polarizing beam splitter and/or one or more optics may be configured downstream of the lateral displacement polarizing beam splitter.

The terms“upstream” and“downstream” relate to an arrangement of items or features relative to the propagation of the light from a light generating means (here the especially the light source(s)), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is“upstream”, and a third position within the beam of light further away from the light generating means is“downstream”. In specific embodiments, the light generating system further comprising a first lens (FE1) configured downstream of the light generating device and upstream of the lateral displacement polarizing beam splitter, wherein the first lens (FE1) is configured to homogenize the beam of light (of the light source, i.e. the elongated body).

Especially, yet further the light generating system comprising a second lens (FE2) configured downstream of the first lens (FE1) and upstream of the lateral displacement polarizing beam splitter, wherein the second lens (FE2) is configured to homogenize the beam of light (of the light source, i.e. the elongated body).

The first lens may in embodiments comprise of an array of small lenses (such as micro lenses). The second lens may in embodiments (also) comprise an array of small lenses (such as micro lenses). Especially, the first lens and the second lens are essentially aligned. In embodiments, the first lens may image the source (i.e. the elongated body, with optional collimator) on the entrance of each small lens of the second lens. The size of this image may especially be essentially exactly half of the size of one small lens (such as micro lenses) of the second lens.

As indicated above, the first lens and the second lens especially both comprise fly eye lenses and may be used to homogenize the beam.

Alternative (or additional) to the two fly eye lenses, a light pipe may be applied.

In specific embodiments, the lateral displacement polarizing beam splitter may comprise an array of lateral displacement polarizing beam splitter elements (see also above), wherein the one or more fly eye lenses are configured to focus the luminescent material light on the respective lateral displacement polarizing beam splitter elements.

Downstream of the second lens and downstream of the polarizing beam splitter (PBS), a condenser lens may be configured, which may image all small lenses of the first lens on the LCD panel.

Hence, in embodiments the light generating system may further comprise one or more fly eye integrating lenses.

As indicated above, the light generating system may especially be used as projector system or as light source in a projector system. Possible aspect ratios of some LCD panels are e.g. 4:3, 16:10, 16:09, 21 :9, 32:9 or 256:135. In principle, other aspect ratios may also be used, though in general the aspect ratios will be between about 1.3 (such as with an aspect ratio of 4:3) and 4 (3.6 for an aspect ratio of 32:9). Presently, the lowest aspect ratio is

4:3. With the present invention, the light source can have an essentially higher aspect ratio. Hence, the first aspect ratio is at least 2.5, such as at least 2.9, like at least 3. Amongst others, this may allow wider elongated bodies. This may e.g. allow using more pump light sources, and thus higher intensities. Also, smaller etendues may be achieved with the present invention, which is useful in the entire projector system, as the optics in the system may be smaller.

Therefore, in yet further embodiments the light generating system may further comprise a liquid crystal panel. The liquid crystal panel may herein also be indicated as “liquid crystal display”,“LCD” or“LC panel”. The term“liquid crystal panel” may also refer to a plurality of (different) liquid crystal panels (such as for different colors of light; see also below).

The aspect ratio of the LC panel may be as indicated above. In general, the liquid crystal panel has a second height (H2), a second width (W2) defining a second aspect ratio AR2=W2/H2. Especially, the LC panel is configured downstream of the displacement polarizing beam splitter (and thus also downstream of the second lens). As indicated above, due to the use of the lateral displacement polarizing beam splitter, the aspect ratio of the elongated luminescent body may be larger, may even be about twice as large, as the aspect ratio of the LC panel. Hence, ARl>AR2. Hence, in specific embodiments the light generating system may further comprise a liquid crystal panel having a second height (H2), a second width (W2) defining a second aspect ratio AR2=W2/H2, wherein the liquid crystal panel is configured (downstream of the lateral displacement polarizing beam splitter and/or downstream of the second lens (FE2), wherein ARl>AR2.

Nevertheless, in view of some desired overfill of the LCD, the aspect ratio of the elongated luminescent body may not be precisely twice as large, but may be slightly smaller. Overfill is desired in view of tolerances. When there is no overfill, there is essentially no tolerance. Hence, with a small overfill, tolerances may easily be accepted. Therefore, 0.5*Wl/Hl=(W2+5l)/(H2+ 52), wherein 51 and 52 are overfill parameters and each independently may be in the range of 0-0.6*W2 and 0-0.6*H2, respectively. The values chosen for 51 and 52 may thus depend upon the desired overfill (with 0 having no overfill), and may be chosen by person skilled in the art. In specific embodiments, 51 is selected from the range of 0-0.01 *W2 and/or 52 is selected from the range of 0-0.01 *H2. In embodiments, 51 and 52 each independently may be in the range of about 0-20 mm, such as in the range of about 0-5 mm. In further embodiments, 51 and 52 are essentially equal. Especially, in the present invention the width of the radiation exit window and the width of the LCD are configured parallel (likewise the heights may be configured parallel).

It may be desirable to illuminate the elongated luminescent body at only one face thereof, and use the other faces e.g. for dissipation of heat (via a heat transfer element, which may be heat sink or which may be in thermal contact with a heat sink). Further, as indicated above, the elongated luminescent body especially has rectangular cross-section. Therefore, in specific embodiments the elongated luminescent body comprises a plurality of N side faces, wherein the plurality of light sources are configured to provide the light source light to only one of the N side faces, wherein N=4, and wherein the light sources of the plurality of light sources comprise solid state light sources.

One or more other faces may thus be in thermal contact with one or more heat transfer elements. Therefore, in embodiments the light generating system may further comprise one or more heat transfer elements configured at a first average distance (dl l) selected from the range of 0.5-50 pm. smaller average distance, however, may also be possible, such as 0.1-0.5 pm. Further aspects of heat transfer elements and the desired minimum and maximum distances are elucidated below.

The elongated luminescent body has a length (L). Especially, the elongated luminescent body comprises a first face and a second face defining a length (L) of the elongated luminescent body, wherein the second face comprises the radiation exit window. In embodiments, the light sources may be configured at one face of the elongated luminescent body, and at the opposite face, a reflector is available to reflect light source light that has travelled through the elongated luminescent body and escapes at the opposite face, back into the luminescent body. Therefore, in embodiments the elongated luminescent body is configured over at least part of its length (L) between the plurality of light sources and a reflector being reflective for at least part of the light source light.

As the width of the elongated luminescent body may e.g. be over 1.5 mm, such as at least about 2 mm, it may further be possible to arrange more than one solid state light source over the width of the elongated luminescent body. Hence, instead of a single array of solid state light sources, a plurality of arrays, such as (at least) two arrays of solid state light sources may be configured over at least part of the length of the elongated luminescent body, while all these light sources illuminate a single face of the elongated luminescent body. Hence, in embodiments the plurality of light sources are configured in a 2D array. Especially, all light sources are configured in the same plane. As further elucidated below, the light sources are especially solid state light sources, such as LEDs.

In embodiments, at backside of the elongated luminescent body, also a reflector may be configured. Therefore, in embodiments the light generating system may further comprise a reflector configured to reflect light selected from the group of light source radiation and luminescent material radiation that has escaped from the first face back into the elongated luminescent body, especially at least luminescent material radiation).

In an aspect, the invention also provides a luminaire comprising the system as defined herein.

As indicated above the light generating system may in embodiments be configured as projector system or may be comprised by a projector system. Therefore, in an aspect the invention also provides a projector system comprising the light generating system as defined herein. The light projector system may also include a plurality of such light generating systems.

The projector system (or light generating system) may be configured to provide (at least) three different colors, such as blue, green, and red. Assuming e.g. a cerium based garnet, the luminescence generated by the elongated luminescent body may comprise green and red, which may be separated from each other with the aid of a color wheel and/or with the aid of another color separation optics, like one or more dichroic mirrors. When dichroic mirrors are used, a scanning prism may be used to sequentially provide the different colors on a single LCD, or two or more LCDs, especially three LCDs may be applied, to control the different colors, which are downstream of the LCDs combined via an integrated (such as a prism). Therefore, in further embodiments of the (projector system), the system may (further) comprise one or more liquid crystal panels (see also above), may comprise one or more of the lateral displacement polarizing beam splitters, may further comprise color separation optics configured to split the luminescent material light into k beams of light of different colors, wherein k is at least two, wherein the color separation optics is (are) configured downstream of the light generating device and upstream of the one or more liquid crystal panels, wherein the color separation optics and optional further optics are configured to provide the k beams of light sequentially to one liquid crystal panel or simultaneously to k liquid crystal panels. Especially, k may be two or three.

To provide three colors, there is a plurality of options. In the context of the present invention, blue may especially be provided directly. Hence, via at least a partially separate optical path, blue light is provided that is not converted. Lor instance, it may in embodiments be possible to use the same type of light sources as for the conversion, but configured such light sources not in a light receiving relationship with the elongated luminescent body. Such light source may also be indicated as additional light source.

At least one of the other colors may be provided by the combination of the light sources and the elongated luminescent body. The other of the other colors may be provided in one or more different ways. In embodiments, also the other of the other colors is provided with an additional light source. Hence, in embodiments there may be two types of different additional light sources alternatively or additionally, the luminescent material light is separated into the two different colors. To this end, the above-mentioned color separation optics may be applied, which may in embodiments comprise a color wheel and which may in other embodiments comprise one or more dichroic mirrors.

This leads to (at least) three different types of light, further indicated as RGB. The RGB light may be provided to one LCD, especially sequentially. In other embodiments, however, the RGB may be provided to (at least) three different LCDs. The latter

embodiments are especially desirable. In the latter embodiments, the RGB light may be combined downstream from the (at least) three different LCDs. To this end, an integrator, such as a dichroic X-cross, may be applied. In this way, in embodiments the three subpixels are combined to pixel. Upstream of the LCD(s) a micro lens array (micro lens arrays) may be configured, especially to optimize the distribution of the light over the LCD (pixels).

Hence, in a specific embodiment the projector system may further comprise an additional light source configured to generate blue additional light source light, wherein the light generating system is configured to generate lighting system light comprising green and red, wherein the color separation optics and optional further optics are configured to provide the two beams of light sequentially to two liquid crystal panels, wherein the projector system is further configured to provide the blue additional light source light to a further liquid crystal panel, and wherein the projector system further comprises integrating optics configured downstream of the three liquid crystal display panels.

Further embodiments of the light generating system and/or the projector system are further elucidated below.

In embodiments, the system further comprises a body holder structure, wherein the body holder structure comprises an elongated slit (“slit”) for hosting the elongated luminescent body. The rod and rod holder combination may in embodiments form a subassembly. This subassembly can be thermally connected to other parts, e.g. an own heat sink, or can be thermally coupled to another part e.g. the LED board, which than forms the thermal interface. Furthermore, a heat sink structure can be integrated into the rod holder to further increase thermal performance, whilst lowering part-count and thus cost. Hence, in embodiments the light generating system comprises a body holder structure. The body holder structure comprises an elongated slit for hosting the elongated luminescent body. Hence, the luminescent body fits in the elongated slit. The body holder structure may comprise a body holder structure length. The slit may have a slit length. The slit length and body holder structure length are essentially the same, i.e. the slit is available over the entire length of the body holder structure. In other embodiments, the slit length may be shorter. In general, however, the slit extends to at least one of the edges of the body holder structure. The slit may be open at least one side. In this way, the elongate body can be provided in the slit in a direction perpendicular to an axis of elongated of the elongated body and the elongated slit. Essentially, the slit has a cross-sectional shape that has the same shape as the luminescent body. For instance, when for instance the luminescent body has a rectangular cross-section shape, the slit will have a shape wherein the rectangular body fits with slit faces parallel to two or more, such as three, side faces of the luminescent body. Hence, the elongated slit is especially configured for hosting the elongated luminescent body.

In specific embodiments the elongated luminescent body comprises a first face and a second face defining a length (L) of the elongated luminescent body, wherein the second face comprises the radiation exit window, wherein the elongated luminescent body comprises a plurality of N side faces. Especially, N=4 (such as especially a rectangular or (rectangular) square cross-section). Further, in specific embodiments the elongated slit may comprises N-l slit side faces (or less than N-l, but at least two), wherein one or more of the (N-l (or less than N-l, but at least two)) side faces are in thermal contact with one or more of the slit side faces. For instance, assuming an elongated luminescent body having a rectangular cross-section, and the slit also having a rectangular cross-section, one or two side faces of the elongated luminescent body may be in thermal contact with one or two slit side faces, respectively. When the elongated luminescent body has a rectangular cross-section, especially four side faces are configured perpendicular to the first face.

Especially, only limited physical (or no) contact between the slit side faces and the face of the elongated luminescent body is desirable. By reducing the physical contact, optical radiation losses through evanescent waves may be minimized. Especially, the arrangement is such, that in general the distance between the face and the respective slit side face is large enough to prevent optical contact, such as at least 1 pm, like at least 2 pm (see also below), but small enough to have thermal contact, such as at maximum about 100 pm. This may be achieved by distance holders, using a rough or roughened surface, etc. (see also further below). Hence, in specific embodiments a side face in thermal contact with a slit side face is configured at a first average distance (dl 1) of at least 1 pm from the slid side face, like at least 2 pm, such as at least 10 pm, up to about 100 pm. Hence, in embodiments the average distance may be selected from the range of 1 pm < dl < 100 pm, such as 1 pm < dl < 50 pm, like about 2 pm < dl < 20 pm. This may apply to each thermal contact between a side face of the elongated luminescent body and a side face of the slit, or other configurations of (other) items that are in thermal contact.

As indicated above, in embodiments two of the side faces are in thermal contact with two of the slit side faces.

Especially for those side faces of the slit that are in thermal contact with the elongated luminescent body, it may be desirable that such slit side faces comprise a reflector. Hence, in embodiments such slit side face may be provided with a reflector (being reflective for especially the light source light, but especially also for the luminescent material light). Alternatively, or additionally, one or more slit side faces may have light reflective properties due to the fact that a light reflective material is applied for the body holder structure, or at least the part of the body holder structure that provides the slit. Hence, in embodiments one or more of the slit side faces being in thermal contact with one or more of the side faces comprises one or more reflectors being reflective for at least part of the light source light (and for at least part of the luminescent material light), and wherein at least a slit side face configured opposite of the light sources (with the elongated luminescent body configured between that slit side face and the light sources), comprises a reflector. Hence, especially the slit side face opposite of the plurality of light sources comprises such a reflector. As further explained below, this may also allow for reduction of the activator content in the elongated luminescent body, as light effectively has an optical path essentially twice as large as the situation without such reflector opposite of the light sources (with the elongated luminescent body in-between).

For achieving thermal contact and essentially no optical contact, the reflector may comprise elevations (to keep the elongated luminescent body at a distance from the (main part of the) reflector or distance holders may be used to configure the elongated luminescent body at a distance from the reflector.

Especially, the light sources of the plurality of light sources are configured at a second shortest distance (d2l) of at least 1 pm, such as at least 2 pm, like at least 10 pm from the radiation input face, such as even at least 100 pm. This prevents an optical contact with the elongated luminescent body, and when the second shortest distance is relatively long, also thermal contact may be low or absent (which allows the use of two thermally different pathways for the elongated luminescent body and the light sources, respectively). Also, optical in-coupling efficiency of the light originating from the light source(s) may be maximized by minimizing the second shortest distance (d2l). Hence, in embodiments 10 pm <d2l<l00 pm.

Furthermore, one may also provide a reflector at the first face (or end face) of the elongated luminescent body. Therefore, in embodiments the light generating system may further comprising a reflector configured to reflect light selected from the group of light source radiation and luminescent material radiation that has escaped from the first face back into the elongated luminescent body.

The body holder structure may comprise one or more heat transfer elements. Alternatively, or additionally, the body holder structure is thermally coupled to one or more heat transfer elements. In specific embodiments, the body holder structure is a monolithic body. The monolithic body may comprise a heat transfer element. Alternatively, or additionally, the monolithic body may be thermally coupled to one or more heat transfer elements. Examples of heat transfer elements are further described below.

For instance, in embodiments the body holder structure may include an aluminum body with the slit. This may provide good thermal (heat sinking) properties as well as the body may provide reflectance. The aluminum body may be coated to enhance reflectivity and/or improve durability.

As indicated above, it may be useful to decouple the thermal management of the light sources and of the elongated luminescent body. This is possible with the present invention. Hence, the light sources or their substrate(s) may be thermally coupled to other heat transfer elements than those mentioned above in relation to the body holder structure.

Hence, in embodiments the light generating system may comprise one or more second heat transfer elements for guiding away heat from the plurality of light sources. These second heat transfer elements may be coupled to a substrate with one or more light sources. Hence, especially the light sources are thermally coupled to one or more (second) heat transfer elements.

It appears that with the present system, the temperature of the elongated luminescent body can be substantially reduced when compared to a system where the heat pathways are not separated. This appears also to lead to a higher efficiency of the system. Hence, in embodiments the one or more heat transfer elements and the one or more second heat transfer elements are thermally coupled.

In alternative embodiments, the one or more heat transfer elements and the one or more second heat transfer elements are not thermally coupled. In this embodiment, the temperature and especially the thermal management of the light sources may be decoupled from the temperature and especially the thermal management of the elongated luminescent body. Hence, in embodiments one or more heat sinks may be thermally coupled (either directly or via a heat transfer element) to the elongated body and one or more other heat sinks may be thermally coupled (either directly or via a heat transfer element) to the light sources (wherein the one or more heat sinks and one or more other heat sinks are not thermally coupled (via a heat transfer element)).

Here below, some aspects of heat transfer elements are described. As indicated above, such heat transfer element may be comprised by the body holder structure or may be used to guide away heat from the light sources. Especially, embodiments are described in relation to guiding away heat from the elongated luminescent body. Further specific embodiments of the heat transfer element(s) are elucidated below.

In embodiments, one or more heat transfer elements are in thermal contact with one or more side faces and are especially configured to transfer heat away (from the luminescent body) during operation of the light generating system. Likewise, in

embodiments, one or more heat transfer elements are in thermal contact with one or more light sources (or a substrate with one or more light sources) and are especially configured to transfer heat away during operation of the light generating system.

Therefore, the heat transfer element(s) may also be indicated as“cooling element(s)”. Hence, in embodiments the heat transfer element(s) may be heatsinks or may be functionally coupled to heatsinks. Especially, the one or more heat transfer elements comprise a thermally conductive material, such as having a thermal conductivity of at least about 20 W/m/K, like at least about 30 W/m/K, such as at least about 100 W/m/K, like especially at least about 200 W/m/K.

Especially, the one or more heat transfer elements are configured parallel to at least part of one or more of the side faces over at least part of the length (L) of the

(elongated) luminescent body. Further, especially the one or more heat transfer elements are configured at a shortest distance (dl) from the respective one or more side faces with 1 pm < dl < 100 pm. In this way, there may essentially no physical contact, which may lead to undesired outcoupling of the light source light and/or the luminescent material light, while there is a good thermal coupling. Especially, the shortest distance (dl) is selected from the range of 2 pm < dl < 50 pm. Hence, when the shortest distance is at least 1 pm, there may essentially be no optical contact.

The one or more heat transfer elements may comprise one or more heat transfer element faces directed to one or more side faces. As indicated above, especially there is no physical contact. However, in embodiments there may be physical contact, but only part of a face of the luminescent body is in contact with part of the one or more heat transfer elements. Hence, in embodiments at least part of the one or more heat transfer element faces of the respective one or more heat transfer elements is in physical contact with the elongated luminescent body. Especially, in such embodiments the shortest distance (dl) is an average distance. Hence, in embodiments the one or more heat transfer elements are configured at an average shortest distance (dl) from the respective one or more side faces with 1 pm < dl < 100 pm.

The one or more heat transfer elements may be configured as a monolithic heat transfer element. For instance, such monolithic heat transfer element may include a cavity, such as a slit, wherein the luminescent body may be configured. In this way, the monolithic heat transfer element may enclose N-l side faces of the luminescent body. Hence, in embodiments the one or more heat transfer elements are at least in thermal contact with all side faces other than the first side face, and wherein the one or more heat transfer elements are configured as a monolithic heat transfer element. Optionally, part of the one or more heat transfer elements may also be in thermal contact with the first side face. Further, in specific embodiments the one or more heat transfer elements, such as especially the monolithic heat transfer element, may be configured in thermal contact with a support for the light source. In embodiments, this support may be thermally conductive, such as having a thermal conductivity as indicated above. The monolithic heat transfer element may also be indicated as integrated heat transfer unit. The term“monolithic heat transfer element” may also refer to a plurality of (different) monolithic heat transfer elements.

Further, the reflector is especially configured at the second side face (and other faces that are not the radiation input face) and configured to reflect light source light escaping from the elongated luminescent body via second face back into the elongated luminescent body. This reflected light may be converted light as well as light source light that is used to illuminate the radiation input face, but that remains unabsorbed during propagation through the luminescent body. With such system, relative to some prior art systems the efficiency can be improved, thermal management may be better, and the system may (therefore) operate more reliably.

Above, and also below, the heat transfer elements are especially described in relation to the heat transfer of the elongated body. However, the above embodiments may in general also apply to heat transfer element in relation to the light sources (or a substrate with light sources).

An important issue of high lumen density (HLD) devises is the cooling of the luminescent rod. In a configuration with two-sided illumination, and a rod with a rectangular cross-section, only two sides are available for this. In that case, the maximum performance is (to some extend) limited by thermal quenching effects that occur in the luminescent rod. In a configuration with single-sided illumination, three sides are available, enabling better cooling. Furthermore, by implementing single-sided illumination combined with the 3-sided cooling of the rod, a single cooling path can be implemented via the LED board. This means that there is thermal coupling between the rod-cooling means and the LED board/PCB cooling in such a way that all heat is being transferred (e.g. to an external heatsink) through the LED board. This means that no additional cooling path from the rod holder towards the “outside world” is needed. This enables a more compact building form factor of the HLD module, enabling easy implementation in volume-critical systems, which may operate at relatively low optical output powers. Herein, the term“single-sided HLD source” and similar terms may refer to the combination of elongated luminescent body and light sources, wherein the light source illuminate the elongated luminescent body essentially from one side (i.e. one face is irradiated).

On the other hand, in the case of high-power applications, single-sided pumped designs increase the possibility for dedicated luminescent rod cooling separate from the LED-cooling interface, thus e.g. enabling slim form-factor systems.

Another issue relates to the cerium concentration of the rod material. The concentration should be high enough to absorb the incident blue light. However, if it is too high, several detrimental effects may happen, like concentration quenching and reabsorption, all leading to a diminished output of green light and more heat generation.

One advantage of a low cerium concentration is that there is less chance of concentration quenching. At high concentration, cerium sites may be so close to each other that energy is transferred to other sites and has a larger chance to be converted to heat instead of green radiation. Also, temperature quenching (the decrease of green luminescence at higher temperature) in general is lower at low cerium concentration. Another advantage is that, at lower concentration, there is less chance of reabsorption. Part of the converted (green) light can be absorbed in the rod; part of this is emitted again but part is lost (because of a finite quantum efficiency and escape losses). So, at lower concentration, more green light can reach the rod‘nose’. A possible further advantage might be that, at lower cerium

concentration, the local intensity of green light will be smaller. The advantage of this might be that there is less chance of (local) photo saturation caused by excited-state absorption (i.e. loss of green light by absorption in the cerium level reached by blue absorption). Also, if a lower cerium concentration can be implemented and blue light passes the rod twice, the heat generated in the rod during light conversion (Stokes-shift) is more evenly distributed over the total volume. This prevents the formation of localized“hot-spots” in the crystal, preventing local thermal quenching and thermal runaways, which otherwise might result in catastrophic quenching.

The amount if cerium (Ce) that can be incorporated is limited. If the target etendue needs to be decreased the rod size has to decrease. At some point the thickness/Ce concentration combination is such, that the rod is not thick enough to have full conversion of the blue pump light. As Ce concentration cannot be increased, this will lead to decreased performance, i.e. full-conversion cannot be reached. In single-sided, this is solved by the reflecting walls, so smaller etendues are possible using the same Ce concentrations.

Finally, due to the improved cooling of the rod material, it is possible to increase the incident blue flux onto this material. It is thus possible to drive the blue pumping LEDs at a higher output level, or use LEDs that already have a higher output flux. By doing so, a higher output flux from the HLD module can be achieved, while the temperature of the converter rod can still be kept below its critical quenching temperature. Hence, a system is obtained that is less thermally critical and thus can be operated at higher output fluxes.

Especially, the light generating system comprises a light source configured to provide light source light. The light source is especially a solid state light source, such as a LED. The light source especially provides light source light having a peak maximum at or close to the excitation maximum of the luminescent material. Therefore, in embodiments wherein the luminescent material has an excitation maximum k _xm , wherein the light sources are configured to provide the source light with an intensity maximum l _rc , wherein l _chi -10 nm< l _rc < k _xm +10 nm, especially wherein l _chi -5 nm< l _rc < l _chi +5 nm, such as wherein l _chi 2.5 nm< l _rc < l _chi +2.5 nm. Especially, the light source wavelength is at wavelengths with at least an (excitation) intensity of 50% of the excitation maximum (intensity), such as at least 75% of the excitation maximum (intensity), such as at least 90% of the excitation maximum (intensity) (of the excitation maximum of the luminescent material). Especially, the light source is configured with its optical axis perpendicular to the first side face, especially perpendicular the radiation input face (see further also below). Further, especially a plurality of light sources is applied. Hence, in specific embodiments the light sources have optical axes configured perpendicular to the first side face, especially perpendicular the radiation input face. Further, especially a single side face is illuminated with the light source light when n=4.

Further embodiments of the light sources and their application are also elucidated below.

As indicated above, the light generating system especially comprises a luminescent body, especially an elongated luminescent body, having a length (F), the (elongated) luminescent body comprising (n) side faces over at least part of the length (F), wherein n>3. Hence, especially the (elongated) luminescent body has a cross-sectional shape (perpendicular to an axis of elongation) that is square (n=4), rectangular (n=4), hexagonal (n=6), or octagonal (n=8), especially rectangular. Would the luminescent body have a circular cross-section, N may be considered ¥. The (elongated) body includes a first end or first face, in general configured perpendicular to one or more of the (n) side faces and a second end or second face, which may be configured perpendicular to one or more of the side faces, and thus parallel to the first face, but which also may be configured under an angle unequal to 90° and unequal to 180°. The (elongated) luminescent body thus includes (n) side faces, which comprise a first side face, comprising a radiation input face, and a second side face configured parallel to the first side face, wherein the side faces define a height (H). The first and the second side face are configured parallel with luminescent body material in between, thereby defining the width of the luminescent body. The radiation input face is at least part of the first face which may be configured to receive the light source light. The (elongated) luminescent body further comprises a radiation exit window bridging at least part of the height (h) between the first side face and the second side face. Especially, the radiation exit window is comprised by the second face. Further embodiments are also elucidated below.

Yet further, the elongated luminescent body comprises a garnet type A3B5O12 luminescent material comprising trivalent cerium (Ce ³⁺ ), with a height dependent

concentration selected from a concentration range defined by a minimum concentration ymin=0.036*h ¹ and a maximum concentration y _max =0.l7 ^i: h ¹ , wherein y is the trivalent cerium concentration in % relative to the A element, and wherein h is the height in mm. Further, especially the height is selected from the range of 0.1 - 100 mm, such as 0.1 -20 mm, like 0.1- 10 mm, such as 0.5-2 mm. For instance, A may be yttrium. When e.g. the height is 1 mm, then h=l, as the height is in mm, leading to a possible concentration range which is 0.036- 0.17%. Would however the height be 0.1 mm, then the concentration range from which the concentration can be selected is 0.36-1.7%. Would the concentration be indicated with y, then A can be replaced by Ai_ _x /iooCe _x /ioo. For instance, would x be 2.2 (see example), then this would result in A0.978Ce0.022.

In embodiments, A comprises one or more of yttrium, gadolinium and lutetium, and wherein B comprises one or more of aluminum and gallium. In embodiments, wherein A=Lu and wherein B=Al, or wherein A comprises Y and Lu, and wherein B=Al.

The element A, as well as (further) embodiments of the garnet, are further elucidated below.

The garnet type A3B5O12 luminescent material is configured to convert at least part of the light source light into converter light. Especially, the garnet material is a material that has an absorption band in the range of 400-500 nm, such as with a maximum in the range of 420-480 nm. Upon excitation with the light source light, the luminescent material generates emission, with one or more wavelengths selected from especially the range of 500- 800 nm, as known in the art. Further embodiments are also elucidated below.

The light generating system may comprise an optical element, wherein the optical element comprises the luminescent body, and optionally other optical elements. The light generating system may also include a plurality of luminescent bodies, wherein one or more, especially all, luminescent bodies are as defined herein. The optical element may include one or more luminescent bodies. Further, the light generating system may include a plurality of optical elements. Further embodiments are elucidated below.

As indicated above, the light generating system further includes a reflector. Especially, such reflector may be configured to reflect light source light escaping from the elongated luminescent body via second face back into the elongated luminescent body. In specific embodiments, the reflector is (thus) especially configured at the second side face. As in embodiments at least part of the one or more heat transfer elements is configured in thermal contact with at least part of the second side face, such reflector may configured between the one or more heat transfer elements or may be comprised by the one or more heat transfer elements.

The one or more heat transfer elements may include one or more (external) faces, which may be indicated as heat transfer element faces. Therefore, in embodiments a heat transfer element face of the one or more heat transfer element may be directed to the second face comprises the reflector. The reflector may comprise a specular mirror, such as an aluminum (coated) mirror. The reflector may also comprise a diffuse reflector, such as a coating of a metal oxide or other reflective material that is (highly) reflective, especially in the visible (spectral range). Hence, the reflective material may be a specular reflective material, such as an aluminum mirror. The reflective material may also be diffuse reflective material, such as a coating of a particulate white material. Suitable reflective material for reflection in the visible may be selected from the group consisting of T1O2, BaS0 ₄ , MgO, AI2O3, and Teflon. Especially, all heat transfer element face that are directed to the luminescent body comprise such reflector. When a heat transfer element face comprises a reflector, the shortest distance between the reflector and the luminescent body may be as defined herein (for the shortest distance between the heat transfer element (face) and the luminescent body).

In specific embodiments, the reflector and the heat transfer element may be the same element. The material of the heat transfer element can have good thermal conductance properties and a high optical reflectivity (>90%) in e.g. the visible spectral range. An example of such a material is AlSiMgMn.

As indicated above, the light generating system may comprise a plurality of light sources to provide light source light that is at least partly converted by the light transmissive body, more especially the luminescent material of the light transmissive body, into converter radiation. The converted light can at least partially escape form the first radiation exit window, which is especially in optical contact with the optical element, more especially the radiation entrance window thereof.

The optical element may especially comprise a collimator used to convert (to “collimate”) the light beam into a beam having a desired angular distribution. Further, the optical element especially comprises a light transmissive body comprising the radiation entrance window. Hence, the optical element may be a body of light transmissive material that is configured to collimate the converter radiation from the luminescent body.

In specific embodiments, the optical element comprises a compound parabolic like collimator, such as a CPC (compound parabolic concentrator).

A massive collimator, such as a massive CPC, may especially be used as extractor of light and to collimate the (emission) radiation. Alternatively, one may also comprise a dome with optical contact (n>l .00) on the nose of the rod or a hollow collimator, such as a CPC, to concentrate the (emission) radiation. The optical element may have cross section (perpendicular to an optical axis) with a shape that is the same as the cross-section of the luminescent body (perpendicular to the longest body axis (which body axis is especially parallel to a radiation input face). For instance, would the latter have a rectangular cross section, the former may also have such rectangular cross section, though the dimension may be different. Further, the dimension of the optical element may vary over its length (as it may have a beam shaping function).

Further, the shape of the cross-section of the optical element may vary with position along the optical axis. In a specific configuration, the aspect ratio of a rectangular cross-section may change, preferably monotonically, with position along the optical axis. In another preferred configuration, the shape of the cross-section of the optical element may change from round to rectangular, or vice versa, with position along the optical axis.

As indicated above, first radiation exit window (of the elongated light transmissive body) is in optical contact with the radiation entrance window of the optical element. The term“optical contact” and similar terms, such as“optically coupled” especially mean that the light escaping the first radiation exit window surface area (Al) may enter the optical element radiation entrance window with minimal losses (such as Fresnel reflection losses or TIR (total internal reflection) losses) due to refractive index differences of these elements. The losses may be minimized by one or more of the following elements: a direct optical contact between the two optical elements, providing an optical glue between the two optical elements, preferably the optical glue having a refractive index higher that the lowest refractive index of the two individual optical elements, providing the two optical elements in close vicinity (e.g. at a distance much smaller than the wavelength of the light), such that the light will tunnel through the material present between the two optical elements, providing an optically transparent interface material between the two optical elements, preferably the optically transparent interface material having a refractive index higher that the lowest refractive index of the two individual optical elements, the optically transparent interface material might be a liquid or a gel or providing optical Anti Reflection coatings on the surfaces of (one or both of) the two individual optical elements. In embodiments, the optically transparent interface material may also be a solid material. Further, the optical interface material or glue especially may have a refractive index not higher than the highest refractive index of the two individual optical elements.

Instead of the term“in optical contact” also the terms“radiationally coupled” or“radiatively coupled” may be used. The term "radiationally coupled" especially means that the luminescent body (i.e. the elongated light transmissive body) and the optical element are associated with each other so that at least part of the radiation emitted by the luminescent body is received by the luminescent material. The luminescent body and the optical element, especially the indicated“windows” may in embodiments be in physical contact with each other or may in other embodiments be separated from each other with a (thin) layer of optical glue, e.g. having a thickness of less than about 1 mm, preferably less than 100 pm. When no optically transparent interface material is applied, the distance between two elements being in optical contact may especially be about at maximum the wavelength of relevance, such as the wavelength of an emission maximum. For visible wavelengths, this may be less than 1 pm, such as less than 0.7 pm, and for blue even smaller. Hence, to obtain optical contact between two elements for e.g. for light with a wavelength l, the two elements may be in physical contact or at an average maximum distance of l, such as at maximum 0.5 *l. Hence, for optical contact herein the distances may be smaller than about 1 pm, like smaller than about 0.7 pm, like smaller than about 0.5 pm, such as at maximum about 0.4 pm (assuming e.g. blue light).

Likewise, the light sources are radiationally coupled with the luminescent body, though in general the light sources are not in physical contact with the luminescent body (see also below). As the luminescent body is a body and as in general also the optical element is a body, the term“window” herein may especially refer to side or a part of a side.

Hence, the luminescent body comprises one or more side faces, wherein the optical element is configured to receive at the radiation entrance window at least part of the converter radiation that escapes from the one or more side faces.

This radiation may reach the entrance window via a gas, such as air directly. Also the radiation may be delivered via another interface material such as a liquid or transparent solid interface material. Additionally or alternatively, this radiation may reach the entrance window after one or more reflections, such as reflections at a mirror positioned nearby the luminescent body. Hence, in embodiments the light generating system may further comprise a first reflective surface, especially configured parallel to one or more side faces, and configured at a first distance from the luminescent body, wherein the first reflective surface is configured to reflect at least part of the converter radiation that escapes from the one or more side faces back into the luminescent body or to the optical element. The space between the reflective surface and the one or more side faces comprises a gas, wherein the gas comprises air. The first distance may e.g. be in the range of 0.1 pm - 20 mm, such as in the range of 1 pm - 10 mm, like 2 pm - 10 mm. Especially, the distance is at least wavelength of interest, more especially at least twice the wavelength of interest. Further, as there may be some contact, e.g. for holding purposes or for distance holder purposes, especially an average distance is at least l,, such as at least 1.5* h like at least 2* h such as especially about 5* h wherein h is the wavelength of interest. Especially, however, the average distance is in embodiments not larger than 50 pm, such as not larger than 25 pm, like not larger than 20 pm, like not larger than 10 pm, for purposes of good thermal contact. Likewise, such average minimum distance may apply to a reflector and/or optical filter configured at e.g. an end face, or other optical components as well. Optionally, in embodiments an element may comprise both heat sinking function a reflection function, such as a heat sink with a reflective surface, or a reflector functionally coupled to a heat sink.

The light generating system may be configured to provide blue, green, yellow, orange, or red light, etc.. Alternatively or additionally, in embodiments, the light generating system may (also) be configured to provide one or more of UV, such as near UV (especially in the range of 320-400 nm), and IR, such as near IR (especially in the range of 750-3000 nm). Further, in specific embodiment, the light generating system may be configured to provide white light. If desired, monochromaticity may be improved using optical filter(s). The definitions of near UV and near infrared may partly overlap with the generally used definition for visible light, which is 380-780 nm.

The term“light concentrator” or“luminescent concentrator” is herein used, as one or more light sources irradiate a relative large surface (area) of the light converter, and a lot of converter radiation may escape from a relatively small area (exit window) of the light converter. Thereby, the specific configuration of the light converter provides its light concentrator properties. Especially, the light concentrator may provide Stokes-shifted light, which is Stokes shifted relative to the pump radiation. Hence, the term“luminescent concentrator” or“luminescent element” may refer to the same element, especially an elongated light transmissive body (comprising a luminescent material), wherein the term “concentrator” and similar terms may refer to the use in combination with one or more light sources and the term“element” may be used in combination with one or more, including a plurality, of light sources. When using a single light source, such light source may e.g. be a laser, especially a solid state laser (like a LED laser). The elongated light transmissive body comprises a luminescent material and can herein especially be used as luminescent concentrator. The elongated light transmissive body is herein also indicated as“luminescent body”. Especially, a plurality of light sources may be applied. The light concentrator comprises a light transmissive body. The light concentrator is especially described in relation to an elongated light transmissive body, such as a ceramic rod or a crystal, such as a single crystal. However, these aspects may also be relevant for other shaped ceramic bodies or single crystals. In specific embodiments, the luminescent body comprises a ceramic body or single crystal.

The light transmissive body has light guiding or wave guiding properties. Hence, the light transmissive body is herein also indicated as waveguide or light guide. As the light transmissive body is used as light concentrator, the light transmissive body is herein also indicated as light concentrator. The light transmissive body will in general have (some) transmission of one or more of (N)UV, visible and (N)IR radiation, such as in embodiments at least visible light, in a direction perpendicular to the length of the light transmissive body. Without the activator (dopant) such as trivalent cerium, the internal transmission in the visible might be close to 100%.

The transmission of the light transmissive body for one or more luminescence wavelengths may be at least 80%/cm, such as at least 90%/cm, even more especially at least 95%/cm, such as at least 98%/cm, such as at least 99%/cm. This implies that e.g. a 1 cm ³ cubic shaped piece of light transmissive body, under perpendicular irradiation of radiation having a selected luminescence wavelength (such as a wavelength corresponding to an emission maximum of the luminescence of the luminescent material of the light transmissive body), will have a transmission of at least 95%.

Herein, values for transmission especially refer to transmission without taking into account Fresnel losses at interfaces (with e.g. air). Hence, the term“transmission” especially refers to the internal transmission. The internal transmission may e.g. be determined by measuring the transmission of two or more bodies having a different width over which the transmission is measured. Then, based on such measurements the contribution of Fresnel reflection losses and (consequently) the internal transmission can be determined. Hence, especially, the values for transmission indicated herein, disregard Fresnel losses.

In embodiments, an anti-reflection coating may be applied to the luminescent body, such as to suppress Fresnel reflection losses (during the light incoupling process).

In addition to a high transmission for the wavelength(s) of interest, also the scattering for the wavelength(s) may especially be low. Hence, the mean free path for the wavelength of interest only taking into account scattering effects (thus not taking into account possible absorption (which should be low anyhow in view of the high transmission), may be at least 0.5 times the length of the body, such as at least the length of the body, like at least twice the length of the body. For instance, in embodiments the mean free path only taking into account scattering effects may be at least 5 mm, such as at least 10 mm. The wavelength of interest may especially be the wavelength at maximum emission of the luminescence of the luminescent material. The term“mean free path” is especially the average distance a ray will travel before experiencing a scattering event that will change its propagation direction.

The terms“light” and“radiation” are herein interchangeably used, unless clear from the context that the term“light” only refers to visible light. The terms“light” and “radiation” may thus refer to UV radiation, visible light, and IR radiation. In specific embodiments, especially for lighting applications, the terms“light” and“radiation” refer to visible light.

The term UV radiation may in specific embodiments refer to near UV radiation (NUV). Therefore, herein also the term“(N)UV” is applied, to refer to in general UV, and in specific embodiments to NUV. The term IR radiation may in specific

embodiments refer to near IR radiation (NIR). Therefore, herein also the term“(N)IR” is applied, to refer to in general IR, and in specific embodiments to NIR.

Herein, the term“visible light” especially relates to light having a wavelength selected from the range of 380-780 nm. The transmission can be determined by providing light at a specific wavelength with a first intensity to the light transmissive body under perpendicular radiation and relating the intensity of the light at that wavelength measured after transmission through the material, to the first intensity of the light provided at that specific wavelength to the material (see also E-208 and E-406 of the CRC Handbook of Chemistry and Physics, 69th edition, 1088-1989).

The light transmissive body may have any shape, such as beam (or bar) like or rod like, however especially beam like (cuboid like). The light transmissive body, such as the luminescent concentrator, might be hollow, like a tube, or might be filled with another material, like a tube filled with water or a tube filled with another solid light transmissive medium. The invention is not limited to specific embodiments of shapes, neither is the invention limited to embodiments with a single exit window or outcoupling face. Below, some specific embodiments are described in more detail. Would the light transmissive body have a circular cross-section, then the width and height may be equal (and may be defined as diameter). Especially, however, the light transmissive body has a cuboid like shape, such as a bar like shape, and is further configured to provide a single exit window. In a specific embodiment, the light transmissive body may especially have an aspect ratio larger than 1, i.e. the length is larger than the width. In general, the light transmissive body is a rod, or bar (beam), or a rectangular plate, though the light transmissive body does not necessarily have a square, rectangular or round cross-section. In general, the light source is configured to irradiate one (or more) of the longer faces (side edge), herein indicated as radiation input face, and radiation escapes from a face at a front (front edge), herein indicated as radiation exit window. The light source(s) may provide radiation to one or more side faces, and optionally an end face. Hence, there may be more than one radiation input face.

Especially, in embodiments the solid state light source, or other light source, is not in (direct) physical contact with the light transmissive body.

Physical contact (between the light exit window(s) of the light source(s) and the light entrance window(s) of the light transmissive body/bodies) may lead to undesired outcoupling (from the light transmissive body) and thus a reduction in concentrator efficiency. Hence, especially there is substantially no physical contact. If the actual contact area is kept small enough, the optical impact may be negligible or at least acceptable.

Therefore, it may be perfectly acceptable to have some physical contact, e.g. by some small points as resulting from a certain surface roughness, or non-perfectly flat surface, or by some intentionally created“highest spots” on a surface that will define a certain average distance between the two surfaces that don’t extract substantial amounts of light while enabling a short average distance.

Further, in general the light transmissive body comprises two substantially parallel faces, a radiation input face and opposite thereof the opposite face. These two faces define herein the width of the light transmissive body. In general, the length of these faces defines the length of the light transmissive body. However, as indicated above, and also below, the light transmissive body may have any shape, and may also include combinations of shapes. Especially, the radiation input face has an radiation input face area (A), wherein the radiation exit window has a radiation exit window area (E), and wherein the radiation input face area (A) is at least 1.5 times, even more especially at least two times larger than the radiation exit window area (E), especially at least 5 times larger, such as in the range of 2- 50,000, especially 5-5,000 times larger. Hence, especially the elongated light transmissive body comprises a geometrical concentration factor, defined as the ratio of the area of the radiation input faces and the area of the radiation exit window, of at least 1.5, such as at least 2, like at least 5, or much larger (see above). This allows e.g. the use of a plurality of solid state light sources (see also below). For typical applications like in automotive, digital projectors, or high brightness spotlight applications, a small but high radiant flux or luminous flux emissive surface is desired. This cannot be obtained with a single LED, but can be obtained with the present light generating system. Especially, the radiation exit window has a radiation exit window area (E) selected from the range of 1-100 mm ² . With such dimensions, the emissive surface can be small, whereas nevertheless high radiance or luminance may be achieved. As indicated above, the light transmissive body in general has an aspect ratio (of length/width). This allows a small radiation exit surface, but a large radiation input surface, e.g. irradiated with a plurality of solid-state light sources. In a specific embodiment, the light transmissive body has a height (H) selected from the range of 0.5-100 mm, such as 0.5-10 mm. The light transmissive body is thus especially an integral body, having the herein indicated faces.

The generally rod shaped or bar shaped light transmissive body can have any cross-sectional shape, but in embodiments has a cross section the shape of a square, rectangle, round, oval, triangle, pentagon, or hexagon. Generally, the ceramic or crystal bodies are cuboid. In specific embodiments, the body may be provided with a different shape than a cuboid, with the light input surface having somewhat the shape of a trapezoid. By doing so, the light flux may be even enhanced, which may be advantageous for some applications. Hence, in some instances (see also above) the term“width” may also refer to diameter, such as in the case of a light transmissive body having a round cross section.

Hence, in embodiments the elongated light transmissive body further has a height (H) and a height (H), with especially L>W and L>H. Especially, the first face and the second face define the length, i.e. the distance between these faces is the length of the elongated light transmissive body. These faces may especially be arranged parallel.

Further, in a specific embodiment the length (L) is at least 2 cm, like 3-20 cm, such as 4-20 cm, such as at maximum 15 cm. Other dimensions may, however, also be possible, such as e.g. 0.5-2 cm.

Especially, the light transmissive body has a height (H) selected to absorb more than 95% of the light source light. In embodiments, the light transmissive body has a height (H) selected from the range of 0.03-4 cm, especially 0.05-2 cm, such as 0.1 -1.5 cm, like 0.1-1 cm. With the herein indicated cerium concentration, such width is enough to absorb substantially ah light (especially at the excitation wavelength with maximum excitation intensity) generated by the light sources. The light transmissive body may also comprise a tube or a plurality of tubes.

In embodiments, the tube (or tubes) may be filled with a gas, like air or another gas having higher heat conductivity, such as helium or hydrogen, or a gas comprising two or more of helium, hydrogen, nitrogen, oxygen and carbon dioxide. In embodiments, the tube (or tubes) may be filled with a liquid, such as water or (another) cooling liquid.

The light transmissive body as set forth below in embodiments according to the invention may also be folded, bended and/or shaped in the length direction such that the light transmissive body is not a straight, linear bar or rod, but may comprise, for example, a rounded comer in the form of a 90 or 180 degrees bend, a U-shape, a circular or elliptical shape, a loop or a 3-dimensional spiral shape having multiple loops. This provides for a compact light transmissive body of which the total length, along which generally the light is guided, is relatively large, leading to a relatively high lumen output, but can at the same time be arranged into a relatively small space. For example, luminescent parts of the light transmissive body may be rigid while transparent parts of the light transmissive body are flexible to provide for the shaping of the light transmissive body along its length direction. The light sources may be placed anywhere along the length of the folded, bended and/or shaped light transmissive body.

Parts of the light transmissive body that are not used as light incoupling area or light exit window may be provided with a reflector. Hence, in an embodiment the light generating system further comprises a reflector configured to reflect luminescent material radiation back into the light transmissive body. Therefore, the light generating system may further include one or more reflectors, especially configured to reflect radiation back into the light transmissive body that escapes from one or more other faces than the radiation exit window. Especially, a face opposite of the radiation exit window may include such reflector, though in an embodiment not in physical contact therewith. Hence, the reflectors may especially not be in physical contact with the light transmissive body. Therefore, in an embodiment the light generating system further comprises an optical reflector (at least) configured downstream of the first face and configured to reflect light back into the elongated light transmissive body. Alternatively, or additionally, optical reflectors may also be arranged at other faces and/or parts of faces that are not used to couple light source light in or luminescence light out. Especially, such optical reflectors may not be in physical contact with the light transmissive body. Further, such optical reflector(s) may be configured to reflect one or more of the luminescence and light source light back into the light transmissive body. Hence, substantially all light source light may be reserved for conversion by the luminescent material (i.e. the activator element(s) such as especially Ce ³⁺ ) and a substantial part of the luminescence may be reserved for outcoupling from the radiation exit window. The term “reflector” may also refer to a plurality of reflectors.

The one or more reflectors may consist of a metal reflector, such as a thin metal plate or a reflective metal layer deposited on a substrate, such as e.g. glass. The one or more reflectors may consist of an optical transparent body containing optical structure to reflect (part) of the light such as prismatic structures. The one or more reflectors may consist of specular reflectors. The one or more reflectors may contain microstructures, such as prism structures or saw tooth structures, designed to reflect the light rays towards a desired direction.

Preferably, such reflectors are also present in the plane where the light sources are positioned, such that that plane consist of a mirror having openings, each opening having the same size as a corresponding light source allowing the light of that corresponding light source to pass the mirror layer and enter the elongated (first) light transmissive body while light that traverses from the (first) light transmissive body in the direction of that plane receives a high probability to hit the mirror layer and will be reflected by that mirror layer back towards the (first) light transmissive body.

The terms“coupling in” and similar terms and“coupling out” and similar terms indicate that light changes from medium (external from the light transmissive body into the light transmissive body, and vice versa, respectively). In general, the light exit window will be a face (or a part of a face), configured (substantially) perpendicular to one or more other faces of the waveguide. In general, the light transmissive body will include one or more body axes (such as a length axis, a width axis or a height axis), with the exit window being configured (substantially) perpendicular to such axis. Hence, in general, the light input face(s) will be configured (substantially) perpendicular to the light exit window. Thus, the radiation exit window is especially configured perpendicular to the one or more radiation input faces. Therefore, especially the face comprising the light exit window does not comprise a light input face.

For further improving efficiency and/or for improving the spectral distribution several optical elements may be included like mirrors, optical filters, additional optics, etc.

In specific embodiments, the light generating system may have a mirror configured at the first face configured to reflect light back into the elongated light transmissive body, and/or may have one or more of an optical filter, a (wavelength selective) mirror, a reflective polarizer, light extraction structures, and a collimator configured at the second face. At the second face the mirror may e.g. be a wavelength selective mirror or a mirror including a hole. In the latter embodiment, light may be reflected back into the body but part of the light may escape via the hole. Especially, in embodiments the optical element may be configured at a distance of about 0.01-1 mm, such as 0.1-1 mm from the body. This may especially apply for e.g. mirrors, wherein optical coupling is not desired.

When optical coupling is desired, such as with an optical element, like a CPC or a mixing element, downstream of the (part of the) body where the luminescent material is located, an optically transparent interface material may be applied. In yet other embodiments, when no optically transparent interface material is applied, the average distance between two elements being in optical contact may especially be about at maximum the wavelength of relevance, such as the wavelength of an emission maximum. Hence, when optical contact is desired, there may be physical contact. Even in such embodiments, there may be a non-zero average distance, but then equal to or lower than the wavelength of interest.

In specific embodiments, especially when no optical contact is desired, the average distance may be as indicated above but at a few places, for instance for configuration purposes, there may be physical contact. For instance, there may be contact with the edge faces over less than 10%, such as over less than 5% of the total area of the side faces. Hence, the minimum average distance may be as defined e.g. above and if there is physical contact, this physical contact may be with at maximum 10% of the surface area of the surface with which the element (mirror and/or heat sink) is in physical contact, such as at maximum 5%, like at maximum 2%, even more especially at maximum 1%. For instance, for the side faces an average distance may e.g. be between 2 and 10 pm (the lower limit basically determined as being a few times the wavelength of interest; here, assuming e.g. visible light). This may be achieved by having physical contact (to secure that distance) over less than 1% of the total area of that respective side face.

For instance, a heat sink or a reflector, or the relevant surface may have some protrusions, like a surface roughness, by which there may be contact between the surface and the element, but in average the distance is at least l; (or more, see also above)(in order to essentially prevent optical contact), but there is physical contact with equal to or less than 10% of the surface of the body (to which the element may be thermally coupled and/or optically not coupled), especially substantially less.

In embodiments, optical elements may be included at one or more of the side faces. In particular, anti-reflection coatings may be applied to enhance coupling efficiency of the (excitation) light source light and/or (wavelength selective) reflection coatings for the converted light.

Downstream of the radiation exit window, optionally an optical filter may be arranged. Such optical filter may be used to remove undesired radiation. For instance, when the light generating system should provide red light, all light other than red may be removed. Hence, in a further embodiment the light generating system further comprises an optical filter configured downstream of the radiation exit window and configured to reduce the relative contribution of undesired light in the converter radiation (downstream of the radiation exit window). For filtering out light source light, optionally an interference filter may be applied.

In yet a further embodiment, the light generating system further comprises a collimator configured downstream of the radiation exit window (of the highest order luminescent concentrator) and configured to collimate the converter radiation. Such collimator, like e.g. a CPC (compound parabolic concentrator), may be used to collimate the light escaping from the radiation exit window and to provide a collimated or pre-collimated beam of light. Herein, the terms“collimated”,“precollimated” and similar terms may especially refer to a light beam having a solid angle (substantially) smaller than 2p.

As indicated above, the light generating system may comprise a plurality of light sources. These pluralities of light sources may be configured to provide light source light to a single side or face or to a plurality of faces; see further also below. When providing light to a plurality of faces, in general each face will receive light of a plurality of light sources (a subset of the plurality of light sources). Hence, in embodiments a plurality of light sources will be configured to provide light source light to a radiation input face. Also, this plurality of light sources will in general be configured in a row or a plurality of rows. Hence, the light transmissive body is elongated, the plurality of light sources may be configured in a row, which may be substantially parallel to the axis of elongated of the light transmissive body. The row of light sources may have substantially the same length as the elongated light transmissive body. Hence, in the light transmissive body has a length (L) in the range of about 80-120% of the second length of the row of light sources; or the row of light sources has a length in the range of about 80-120% of the length of the light transmissive body.

The light sources may be configured to provide light with a wavelength selected from the range of UV (including near UV), visible, and infrared (including near IR).

Especially, the light sources are light sources that during operation emit (light source light) at least light at a wavelength selected from the range of 200-490 nm, especially light sources that during operation emit at least light at wavelength selected from the range of 360-490 nm, such as 400-490 nm, even more especially in the range of 430-490 nm, such as 440-490 nm, such as at maximum 480 nm. This light may partially be used by the

luminescent material. Hence, in a specific embodiment, the light source is configured to generate blue light. In a specific embodiment, the light source comprises a solid state light source (such as a LED or laser diode). The term“light source” may also relate to a plurality of light sources, such as e.g. 2-2000, such as 2-500, like 2-100, e.g. at least 4 light sources, such as in embodiments especially 4-80 (solid state) light sources, though many more light sources may be applied. Hence, in embodiments 4-500 light sources may be applied, like e.g. 8-200 light sources, such as at least 10 light sources, or even at least 50 light sources. The term“light source” may also relate to one or more light sources that are tailored to be applied for such light concentrating luminescent concentrators, e.g. one or more LED’s having a long elongated radiating surface matching the long elongated light input surfaces of the elongated luminescent concentrator. Hence, the term LED may also refer to a plurality of LEDs. Hence, as indicated herein, the term“solid state light source” may also refer to a plurality of solid state light sources. In an embodiment (see also below), these are substantially identical solid state light sources, i.e. providing substantially identical spectral distributions of the solid state light source radiation. In embodiments, the solid state light sources may be configured to irradiate different faces of the light transmissive body. Further, the term“light source” may in embodiments also refer to a so-called chips-on-board (COB) light source. The term“COB” especially refers to LED chips in the form of a semiconductor chip that is neither encased nor connected but directly mounted onto a substrate, such as a PCB (“printed circuit board”) or comparable. Hence, a plurality of semiconductor light sources may be configured on the same substrate. In embodiments, a COB is a multi LED chip configured together as a single lighting module.

The light generating system comprises a plurality of light sources. Especially, the light source light of the plurality of light sources have spectral overlap, even more especially, they are of the same type and provide substantial identical light (having thus substantial the same spectral distribution). Hence, the light sources may substantially have the same emission maximum (“peak maximum”), such as within a bandwidth of 10 nm, especially within 8 nm, such as within 5 nm (e.g. obtained by binning). However, in yet other embodiments, the light generating system may comprise a single light source, especially a solid-state light source having a relatively large die. Hence, herein also the phrase“one or more light sources” may be applied. In embodiments, there may be two or more different luminescent materials, such as e.g. when applying two or more different light transmissive bodies. In such embodiments, the light sources may comprise light sources with two or more different emission spectra enabling excitation of two different luminescent materials. Such two or more different light sources may belong to different bins.

The light sources are especially configured to provide a blue optical power (W _0pt ) of at least 0.2 Watt/mm ² to the light transmissive body, i.e. to the radiation input face(s). The blue optical power is defined as the energy that is within the energy range that is defined as blue part of the spectrum (see also below). Especially, the photon flux is in average at least 4.5* 10 ¹⁷ photons/(s.mm ² ), such as at least 6.0* 10 ¹⁷ photons/(s.mm ² ).

Assuming blue (excitation) light, this may e.g. correspond to a blue power (W _opt ) provided to at least one of the radiation input faces of in average at least 0.067 Watt/mm ² and 0.2 Watt/mm ² , respectively. Here, the term“in average” especially indicates an average over the area (of the at least one of the radiation input surfaces). When more than one radiation input surface is irradiated, then especially each of these radiation input surfaces receives such photon flux. Further, especially the indicated photon flux (or blue power when blue light source light is applied) is also an average over time.

In yet a further embodiment, especially for (LCD) projector applications using dynamic contrast technologies, such as e.g. described in WO0119092 or USRE42428 (El), the plurality of light sources are operated in video signal content controlled PWM pulsed operation with a duty cycle selected from the range of 0.01-80%, such as 0.1-70%.

In yet a further embodiment, especially for (LCD) projector applications using dynamic contrast technologies, such as e.g. described in US patent WOO 119092 or

US6631995 (B2), the plurality of light sources are operated in video signal content controlled intensity modulated operation with intensity variations selected from the range of 0.1-100%, such as 2-100%.

The light generating system may comprise a plurality of luminescent concentrators, such as in the range of 2-50, like 2-20 light concentrators (which may e.g. be stacked).

The light concentrator may radiationally be coupled with one or more light sources, especially a plurality of light sources, such as 2-1000, like 2-50 light sources. The term "radiationally coupled" especially means that the light source and the light concentrator are associated with each other so that at least part of the radiation emitted by the light source is received by the light concentrator (and at least partly converted into luminescence). Instead of the term“luminescence” also the terms“emission” or“emission radiation” may be applied.

Hence, the luminescent concentrator receives at one or more radiation input faces radiation (pump radiation) from an upstream configured light concentrator or from upstream configured light sources. Further, the light concentrator comprises a luminescent material configured to convert at least part of a pump radiation received at one or more radiation input faces into luminescent material radiation, and the luminescent concentrator configured to couple at least part of the luminescent material radiation out at the radiation exit window as converter radiation. This converter radiation is especially used as component of the light generating system light.

The phrase“configured to provide luminescent material radiation at the radiation exit window” and similar phrases especially refers to embodiments wherein the luminescent material radiation is generated within the luminescent concentrator (i.e. within the light transmissive body), and part of the luminescent material radiation will reach the radiation exit window and escape from the luminescent concentrator. Hence, downstream of the radiation exit window the luminescent material radiation is provided. The converter radiation, downstream of the radiation exit window comprises at least the luminescent material radiation escaped via the radiation exit window from the light converter. Instead of the term“converter radiation” also the term“light concentrator light” may be used. Pump radiation can be applied to a single radiation input face or a plurality of radiation input faces.

In embodiments, the length (L) is selected from the range of 1-100 cm, such as especially 2-50 cm, like at least 3 cm, such as 5-50 cm, like at maximum 30 cm. This may thus apply to all luminescent concentrators. However, the range indicates that the different luminescent concentrators may have different lengths within this range.

In yet further embodiments, the elongated light transmissive body (of the luminescent concentrator) comprises an elongated ceramic body. For instance, luminescent ceramic garnets doped with Ce ³⁺ (trivalent cerium) can be used to convert blue light into light with a longer wavelength, e.g. within the green to red wavelength region, such as in the range of about 500-750 nm, or even in the cyan. To obtain sufficient absorption and light output in desired directions, it is advantageous to use transparent rods (especially substantially shaped as beams). Such rod can be used as light concentrator, converting light source light into converter radiation and providing at an exit surface (a substantial amount of) (concentrated) converter radiation. Light generating systems based on light concentrators may e.g. be of interest for projector applications. For projectors, red, yellow, green and blue luminescent concentrators are of interest. Green and/or yellow luminescent rods, based on garnets, can be relatively efficient. Such concentrators are especially based on YAG:Ce (i.e. YiAfO^CY ) or LuAG, which can be indicated as (Yi_ _x Lu _x ) ₃ Al ₅ 0i ₂ :Ce ³⁺ , where 0<x<l, such as in embodiments Lu ₃ Al ₅ 0i ₂ :Ce ³⁺ .‘Red’ garnets can be made by doping a YAG-gamet with Gd (“YGdAG”). Cyan emitters can be made by e.g. replacing (part of the) Al (in e.g. LuAG) by Ga (to provide“LuGaAG”). Blue luminescent concentrators can be based on YSO

(Y ₂ Si0 ₅ :Ce ³⁺ ) or similar compounds or BAM (BaMgAhoOi ₇ :Eu ²⁺ ) or similar compounds, especially configured as single crystal(s). The term similar compounds especially refer to compounds having the same crystallographic structure but where one or more cations are at least partially replaced with another cation (e.g. Y replacing with Lu and/or Gd, or Ba replacing with Sr). Optionally, also anions may be at least partially replaced, or cation-anion combinations, such as replacing at least part of the Al-0 with Si-N.

Hence, especially the elongated light transmissive body comprises a ceramic material configured to wavelength convert at least part of the (blue) light source light into converter radiation in e.g. one or more of the green, yellow and red, which converter radiation at least partly escapes from the radiation exit window.

In embodiments, the ceramic material especially comprises an AiBsO^CY ceramic material (“ceramic garnet”), wherein A comprises yttrium (Y) and/or lutetium (Lu) and/or gadolinium (Gd), and wherein B comprises aluminum (Al) and/or gallium (Ga), especially at least Al. As further indicated below, A may also refer to other rare earth elements and B may include Al only, but may optionally also include gallium. The formula A ₃ B ₅ O i2:Ce ³⁺ especially indicates the chemical formula, i.e. the stoichiometry of the different type of elements A, B and O (3:5:12). However, as known in the art the compounds indicated by such formula may optionally also include a small deviation from stoichiometry.

In yet a further aspect, the invention also provides such elongated light transmissive body per se, i.e. an elongated light transmissive body having a first face and a second face, these faces especially defining the length (L) of the elongated light transmissive body, the elongated light transmissive body comprising one or more radiation input faces and a radiation exit window, wherein the second face comprises the radiation exit window, wherein the elongated light transmissive body comprises a ceramic material configured to wavelength convert at least part of (blue) light source light into converter radiation, such as (at least) one or more of green, yellow, and red converter radiation (which at least partly escapes from the radiation exit window when the elongated light transmissive body is irradiated with blue light source light), wherein the ceramic material comprises an A ₃ B ₅ O i ₂ :Ce ³⁺ ceramic material as defined herein. Such light transmissive body can thus be used as light converter. Especially, such light transmissive body has the shape of a cuboid.

As indicated above, in embodiments the ceramic material comprises a garnet material. However, also other (crystallographic) cubic systems may be applied. Hence, the elongated body especially comprises a luminescent ceramic. The garnet material, especially the ceramic garnet material, is herein also indicated as“luminescent material”. The luminescent material comprises an A^BsO^Cc (garnet material), wherein A is especially selected from the group consisting of Sc, Y, Tb, Gd, and Lu (especially at least Y and/or Lu, and optionally Gd), wherein B is especially selected from the group consisting of Al and Ga (especially at least Al). More especially, A (essentially) comprises (i) lutetium (Lu), (ii) yttrium, (iii) yttrium (Y) and lutetium (Lu), (iv) gadolinium (Gd), optionally in combination with one of the aforementioned, and B comprises aluminum (Al) or gallium (Ga) or a combination of both. Such garnet is be doped with cerium (Ce), and optionally with other luminescent species such as praseodymium (Pr).

As indicated above, the element A may especially be selected from the group consisting of yttrium (Y) and gadolinium (Gd). Hence, A^BsO^Cc especially refers to (Yi_ _x Gd _x ) ₃ B ₅ 0i ₂ :Ce ³⁺ , wherein especially x is in the range of 0.1-0.5, even more especially in the range of 0.2-0.4, yet even more especially 0.2-0.35. Hence, A may comprise in the range of 50-90 atom %Y, even more especially at least 60-80 atom %Y, yet even more especially 65- 80 atom % of A comprises Y. Lurther, A comprises thus especially at least 10 atom % Gd, such as in the range of 10-50 atom% Gd, like 20-40 atom%, yet even more especially 20-35 atom % Gd.

Especially, B comprises aluminum (Al), however, B may also partly comprise gallium (Ga) and/or scandium (Sc) and/or indium (In), especially up to about 20% of Al, more especially up to about 10 % of Al may be replaced (i.e. the A ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. Therefore, B may comprise at least 90 atom % Al. Hence, A^BsO^Cc especially refers to (Yi- _x Gd _x ) ₃ Al ₅ 0i ₂ :Ce ³⁺ , wherein especially x is in the range of 0.1 -0.5, even more especially in the range of 0.2-0.4.

In another variant, B (especially Al) and O may at least partly be replaced by Si and N. Optionally, up to about 20 % of Al-0 may be replaced by Si-N, such as up to 10%.

Lor the concentration of cerium, the indication n mole % Ce indicates that n% of A is replaced by cerium. Hence, A^BsO^Cc may also be defined as (Ai_ _n Ce _n ) ₃ B ₅ 0i ₂ , with n being in the range of 0.001-0.036, such as 0.0015-0.01. Therefore, a garnet essentially comprising Y and mole Ce may in fact refer to ((Yi- _x Gd _x )i- _n Ce _n ) ₃ B ₅ 0i ₂ , with x and n as defined above.

Especially, the ceramic material is obtainable by a sintering process and/or a hot-pressing process, optionally followed by an annealing in an (slightly) oxidizing atmosphere. The term“ceramic” especially relates to an inorganic material that is - amongst others - obtainable by heating a (poly crystalline) powder at a temperature of at least 500 °C, especially at least 800 °C, such as at least 1000 °C, like at least 1400 °C, under reduced pressure, atmospheric pressure or high pressure, such as in the range of 10 ⁸ to 500 MPa, such as especially at least 0.5 MPa, like especially at least 1 MPa, like 1 to about 500 MPa, such as at least 5 MPa, or at least 10 MPa, especially under uniaxial or isostatic pressure, especially under isostatic pressure. A specific method to obtain a ceramic is hot isostatic pressing (HIP), whereas the HIP process may be a post-sinter HIP, capsule HIP or combined sinter-HIP process, like under the temperature and pressure conditions as indicate above. The ceramic obtainable by such method may be used as such, or may be further processed (like polishing). A ceramic especially has density that is at least 90% (or higher, see below), such as at least 95%, like in the range of 97-100 %, of the theoretical density (i.e. the density of a single crystal). A ceramic may still be poly crystalline, but with a reduced, or strongly reduced volume between grains (pressed particles or pressed agglomerate particles). The heating under elevated pressure, such as HIP, may e.g. be performed in an inert gas, such as comprising one or more of N ₂ and argon (Ar). Especially, the heating under elevated pressures is preceded by a sintering process at a temperature selected from the range of 1400- 1900 °C, such as 1500-1800 °C. Such sintering may be performed under reduced pressure, such as at a pressure of 10 ² Pa or lower. Such sintering may already lead to a density of in the order of at least 95%, even more especially at least 99%, of the theoretical density. After both the pre-sintering and the heating, especially under elevated pressure, such as HIP, the density of the light transmissive body can be close to the density of a single crystal. However, a difference is that grain boundaries are available in the light transmissive body, as the light transmissive body is poly crystalline. Such grain boundaries can e.g. be detected by optical microscopy or SEM. Hence, herein the light transmissive body especially refers to a sintered polycrystalline having a density substantially identical to a single crystal (of the same material). Such body may thus be highly transparent for visible light (except for the absorption by the light absorbing species such as especially Ce ³⁺ ).

The luminescent concentrator may also be a crystal, such as a single crystal. Such crystals can be grown / drawn from the melt in a higher temperature process. The large crystal, typically referred to as boule, can be cut into pieces to form the light transmissive bodies. The polycrystalline garnets mentioned above are examples of materials that can alternatively also be grown in single crystalline form.

After obtaining the light transmissive body, the body may be polished. Before or after polishing an annealing process (in an oxidative atmosphere) may be executed, especially before polishing. In a further specific embodiment, the annealing process lasts for at least 2 hours, such as at least 2 hours at at least 1200 °C. Further, especially the oxidizing atmosphere comprises for example 0 ₂ .

In specific embodiments, the luminescent concentrator may also be another material with light conversion properties such as e.g. quantum dots in glass, nanophosphors in transparent media etc.

The light generating system may further comprise a cooling element in thermal contact with the luminescent concentrator. The cooling element can be a heatsink or an actively cooled element, such as a Peltier element. Further, the cooling element can be in thermal contact with the light transmissive body via other means, including heat transfer via air or with an intermediate element that can transfer heat, such as a thermal grease.

Especially, however, the cooling element is in physical contact with the light transmissive body. The term“cooling element” may also refer to a plurality of (different) cooling elements.

Hence, the light generating system may include a heatsink configured to facilitate cooling of the solid state light source and/or luminescent concentrator. The heatsink may comprise or consist of copper, aluminum, silver, gold, silicon carbide, aluminum nitride, boron nitride, aluminum silicon carbide, beryllium oxide, silicon-silicon carbide, aluminum silicon carbide, copper tungsten alloys, copper molybdenum carbides, carbon, diamond, graphite, and combinations of two or more thereof. Alternatively, or additionally, the heatsink may comprise or consist of aluminum oxide. The term“heatsink” may also refer to a plurality of (different) heatsink. The light generating system may further include one or more cooling elements configured to cool the light transmissive body. With the present invention, cooling elements or heatsinks may be used to cool the light transmissive body and the same or different cooling elements or heatsinks may be used to cool the light sources. The cooling elements or heatsinks may also provide interfaces to further cooling means or allow cooling transport to dissipate the heat to the ambient. For instance, the cooling elements or heatsinks may be connected to heat pipes or a water-cooling systems that are connect to more remotely placed heatsinks or may be directly cooled by air flows such as generated by fans. Both passive and active cooling may be applied.

In specific embodiments, there is no physical contact between the heat sink (or cooling elements) and the light transmissive body. Especially, the average is at least the intensity averaged wavelength of light that is transmitted by luminescence of luminescent material. In embodiments, the average between the light transmissive body and the heatsink or cooling element is at least 1 pm, such as at least 2 pm, like at least 5 pm. Further, for a good heat transfer the average distance between the light transmissive body and the heatsink or cooling elements is not larger than 50 pm, such as not larger than 25 pm, like not larger than 20 pm, such as equal to or smaller than 15 pm, like at maximum 10 pm.

Therefore, in embodiments the light generating system may further comprise a heat sink having an average distance to the elongated light transmissive body of at least 1 pm, such as at least 2 pm, like especially at least 5 pm, or wherein the heat dissipating element is in physical contact with at maximum 10%, such as at maximum 5% of a total area of the side face(s) of the elongated light transmissive body. The average is thus especially not larger than 50 pm. Instead of the term“heat sink” also the term cooling element may be applied.

As indicated above, especially there is an average distance between the elongated luminescent body and the slit side(s). As there are (substantial) parts, or the entire part, of the relevant face of the elongated body, at a distance between the (adjacent) slit face, there may be an air gap in between.

The thickness of the air gap is higher than the wavelength of the light, e.g. higher than 0.1 pm, e.g. higher 0.5 pm, like at least 1 pm, such as at least 2 pm. The elongated luminescent concentrator is secured in the housing by providing small particles between the elongated luminescent concentrator and the housing, such as small spheres or rods having a diameter higher than 0.1 pm, e.g. higher 0.5 pm, like at least 1 pm, such as at least 2 pm, such as at least 5 pm, especially equal to or smaller than 20 pm, such as equal to or smaller than 10 pm (see also above defined average). Alternatively, the elongated luminescent concentrator may be secured in the housing by providing some surface roughness on the surfaces of the highly thermal conductive housing touching the elongated luminescent concentrator, the surface roughness varying over a depth higher than 0.1 pm, e.g. higher 0.5 pm, like at least 1 pm, such as at least 2 pm, especially not larger than 100 mih, even more especially not larger than 50 pm, like not larger than 20 pm, especially equal to or smaller than about 10 pm.

The density of such spheres, rods or touch points of a rough surface of the highly thermal conductive housing is relatively very small, such that most of the surface area of the elongated light transmissive body remains untouched securing a high level of TIR reflections within of the light trapped within the elongated light transmissive body.

The light generating system may thus essentially consist of the elongated light transmissive body comprising a luminescent material and one or more, especially a plurality of light sources, which pump the luminescent material to provide luminescent material light, that escapes from a radiation exit window (of an end face (second face)).

Further, the light generating system may comprise an optical element, such as a CPC or (other) extraction optical element, which may be configured downstream of the light transmissive body, but which in embodiments may be integrated with the light transmissive body.

Optionally, between this optical element and the light transmissive body, a radiation mixing element may be configured. Hence, a section of the light transmissive body of an additional element may be configured that acts as an optical mixing rod (preferably not round, but e.g. hexagonal) between the converters and the CPC (or extraction optical element). Alternatively or additionally, the extraction optical element is designed such that it also mixes the light.

Further, the light generating system may comprise one or more holding elements for holding the light transmissive body. Especially, these holding elements have contact with the edge faces, but only with a small part thereof to minimize losses of light. For instance, the holding element(s), like clamping device (s) have contact with the edge faces over less than 10%, such as over less than 5% of the total area of the side faces. Further, the light generating system may comprise a heat sink and/or a cooling element. The holding element(s) may be comprised by the heat sink and/or cooling element.

Here, the term“light generating system” may also be used for a (digital) projector. Further, the light generating system may be used for e.g. stage lighting (see further also below), or architectural lighting, or be applied in a (fluorescence) microscopy or endoscopy light generating system. Therefore, in embodiments the invention also provides a light generating system as defined herein, wherein the light generating system comprises a digital projector, a stage light generating system or an architectural light generating system. The light generating system may comprise one or more light generating systems as defined herein and optionally one or more second light generating systems configured to provide second light generating system light, wherein the light generating system light comprises (a) one or more of (i) the converter radiation as defined herein, and optionally (b) second light generating system light. Hence, the invention also provides a light generating system configured to provide visible light, wherein the light generating system comprises at least one light generating system as defined herein. For instance, such light generating system may also comprise one or more (additional) optical elements, like one or more of optical filters, collimators, reflectors, wavelength converters, lens elements, etc. The light generating system may be, for example, a light generating system for use in an automotive application, like a headlight. Hence, the invention also provides an automotive light generating system configured to provide visible light, wherein the automotive light generating system comprises at least one light generating system as defined herein and/or a digital projector system comprising at least one light generating system as defined herein. Especially, the light generating system may be configured (in such applications) to provide red light. The automotive light generating system or digital projector system may also comprise a plurality of the light generating systems as described herein.

Alternatively, the light generating system may be designed to provide high intensity UV radiation, e.g. for 3D printing technologies or UV sterilization applications. Alternatively, the light generating system may be designed to provide a high intensity IR light beam, e.g., to project IR images for (military) training purposes.

The term white light herein, is known to the person skilled in the art. It especially relates to light having a correlated color temperature (CCT) between about 2000 and 20000 K, especially 2700-20000 K, for general lighting especially in the range of about 2700 K and 6500 K, and for backlighting purposes especially in the range of about 7000 K and 20000 K, and especially within about 15 SDCM (standard deviation of color matching) from the BBL (black body locus), especially within about 10 SDCM from the BBL, even more especially within about 5 SDCM from the BBL, such as within about 3 SDCM from the BBL.

The elongated light transmissive body, and optionally also the optical element, may comprise light transmissive host material (thus not taking into account the luminescent material, or more especially in embodiments a luminescent species such as trivalent cerium), especially light transparent material for one or more wavelengths in the visible, such as in the green and red, and in general also in the blue. Suitable host materials may comprise one or more materials selected from the group consisting of a transmissive organic material, such as selected from the amorphous polymers group, e.g. PC (polycarbonate), polymethylacrylate (PM A), polymethylmethacrylate (PMMA) (Plexiglas or Perspex), cellulose acetate butyrate (CAB), silicone, PDMS (polydimethylsiloxane), and COC (cyclo olefin copolymer).

Especially, the light transmissive material may comprise an aromatic polyester, or a copolymer thereof, such as e.g. polycarbonate (PC), poly (methyl)methacrylate (P(M)MA), polyglycolide or polyglycolic acid (PGA), polylactic acid (PLA), polycapro lactone (PCL), polyethylene adipate (PEA), polyhydroxy alkanoate (PHA), polyhydroxy butyrate (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN). Hence, the light transmissive material is especially a polymeric light transmissive material.

However, in another embodiment the light transmissive material may comprise an inorganic material. Especially, the inorganic light transmissive material may be selected from the group consisting of glasses, (fused) quartz, transmissive ceramic materials (such as garnets), and silicones. Glass ceramic materials may also be applied. Also, hybrid materials, comprising both inorganic and organic parts may be applied. Especially, the light transmissive material comprises one or more of PMMA, transparent PC, or glass.

When a luminescent material, like an inorganic luminescent material, quantum dots, organic molecules, etc., are embedded in a host matrix, the concentration of the luminescent material may in embodiments be selected from the range of 0.01-5 wt% (weight %), such as 0.01-2 wt%.

High brightness light sources may be used in e.g. front projectors, rear projectors, studio lighting, stage lighting, entertainment lighting, automotive front lighting, architectural lighting, augmented illumination (incl. data/content), microscopy, metrology, medical applications, e.g. digital pathology, etc.

Instead of A3B5O12, the invention may also be applied with another cerium comprising material, such as e.g. M ₂ Si0 ₅ :Ce ³⁺ , wherein M refers to one or more elements selected from the group of lanthanides and yttrium, especially wherein M comprises one or more of Y, La, Gd, and Lu. All embodiments described herein may also be applied in relation to such luminescent material.

Hence, in an aspect the invention provides also lighting device comprising (i) light generating system comprising: (i) a light source configured to provide light source light; (ii) an elongated luminescent body having a length (L), the elongated luminescent body comprising (iia) a plurality of side faces over at least part of the length (L), wherein the side faces comprise a first side face, comprising a radiation input face, and a second side face configured parallel to the first side face, wherein the side faces define a height (H), wherein the elongated luminescent body further comprises a radiation exit window bridging at least part of the height (H) between the first side face and the second side face; (iib) a M2S1O5 type luminescent material comprising trivalent cerium, with a height dependent concentration, especially in embodiments selected from a concentration range defined by a minimum concentration y _m in = 0.036*h ^_1 and a maximum concentration y _m ax = 0.17*tr\ wherein y is the trivalent cerium concentration in % relative to the M element, and wherein h is the height (H) in mm, wherein the M2S1O5 type luminescent material is configured to convert at least part of the light source light into converter light, wherein M refers to one or more elements selected from the group of lanthanides and yttrium, especially wherein M comprises one or more of Y, La, Gd, and Lu; (iii) one or more heat transfer elements in thermal contact with one or more side faces; and (iv) a reflector configured at the second side face and configured to reflect light source light escaping from the elongated luminescent body via second face back into the elongated luminescent body. Especially, M=Y.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts, and in which:

Figs la-lf schematically depict some aspects of the invention; and Fig. 2a schematically shows an embodiment of a cross section of configuration with single-sided illumination of luminescent rod. The inner sides of the cooling block(s) may be made reflective or covered by a mirror;

Fig. 2b provides a schematic representation of single-sided concept;

Figs. 3a-3e schematically depict some aspects of the light generation system and/or projector system;

Fig. 4 schematically depicts an embodiment of the projector system.

The schematic drawings are not necessarily on scale.

DETAIFED DESCRIPTION OF THE EMBODIMENTS

A light emitting device according to the invention may be used in applications including but not being limited to a lamp, a light module, a luminaire, a spotlight, a flashlight, a projector, a (digital) projection device, automotive lighting such as e.g. a headlight or a taillight of a motor vehicle, arena lighting, theater lighting and architectural lighting.

Light sources which are part of the embodiments according to the invention as set forth below, may be adapted for, in operation, emitting light with a first spectral distribution. This light is subsequently coupled into a light guide or waveguide; here the light transmissive body. The light guide or waveguide may convert the light of the first spectral distribution to another spectral distribution and guides the light to an exit surface.

An embodiment of the light generating system as defined herein is schematically depicted in Fig. la. Fig. la schematically depicts a light generating system 1000 comprising a plurality of solid state light sources 10 and a luminescent concentrator 5 comprising an elongated light transmissive body 100 having a first face 141 and a second face 142 defining a length L of the elongated light transmissive body 100. The elongated light transmissive body 100 comprising one or more radiation input faces 111, here by way of example two oppositely arranged faces, indicated with references 143 and 144 (which define e.g. the height H), which are herein also indicated as edge faces or edge sides 147. Further the light transmissive body 100 comprises a radiation exit window 112, wherein the second face 142 comprises the radiation exit window 112. The entire second face 142 may be used or configured as radiation exit window. The plurality of solid-state light sources 10 are configured to provide (blue) light source light 11 to the one or more radiation input faces 111. As indicated above, they especially are configured to provide to at least one of the radiation input faces 111 a blue power W _opt of in average at least 0.067 Watt/mm ² . Reference BA indicates a body axis, which will in cuboid embodiments be substantially parallel to the edge sides 147. Reference 140 refers to side faces or edge faces in general.

The elongated light transmissive body 100 may comprise a ceramic material 120 configured to wavelength convert at least part of the (blue) light source light 11 into converter light 101, such as at least one or more of green and red converter light 101. As indicated above the ceramic material 120 comprises an A^BsO^Cc ^’ ceramic material, wherein A comprises e.g. one or more of yttrium (Y), gadolinium (Gd) and lutetium (Lu), and wherein B comprises e.g. aluminum (Al). References 20 and 21 indicate an optical filter and a reflector, respectively. The former may reduce e.g. non-green light when green light is desired or may reduce non-red light when red light is desired. The latter may be used to reflect light back into the light transmissive body or waveguide, thereby improving the efficiency. Note that more reflectors than the schematically depicted reflector may be used. Note that the light transmissive body may also essentially consist of a single crystal, which may in embodiments also be AiBsO^UU .

The light sources may in principle be any type of light source, but is in an embodiment a solid state light source such as a Light Emitting Diode (LED), a Laser Diode or Organic Light Emitting Diode (OLED), a plurality of LEDs or Laser Diodes or OLEDs or an array of LEDs or Laser Diodes or OLEDs, or a combination of any of these. The LED may in principle be an LED of any color, or a combination of these, but is in an embodiment a blue light source producing light source light in the UV and/or blue color-range which is defined as a wavelength range of between 380 nm and 490 nm. In another embodiment, the light source is an UV or violet light source, i.e. emitting in a wavelength range of below 420 nm. In case of a plurality or an array of LEDs or Laser Diodes or OLEDs, the LEDs or Laser Diodes or OLEDs may in principle be LEDs or Laser Diodes or OLEDs of two or more different colors, such as, but not limited to, UV, blue, green, yellow or red.

The light sources 10 are configured to provide light source light 11, which is used as pump radiation 7. The luminescent material 120 converts the light source light into luminescent material light 8 (see also Lig. le). Light escaping at the light exit window is indicated as converter light 101, and will include luminescent material light 8. Note that due to reabsorption part of the luminescent material light 8 within the luminescent concentrator 5 may be reabsorbed. Hence, the spectral distribution may be redshifted relative e.g. a low doped system and/or a powder of the same material. The light generating system 1000 may be used as luminescent concentrator to pump another luminescent concentrator.

Ligs. la- lb schematically depict similar embodiments of the light generating system. Lurther, the light generating system may include further optical elements, either separate from the waveguide and/or integrated in the waveguide, like e.g. a light

concentrating element, such as a compound parabolic light concentrating element (CPC). The light generating systems 1000 in Lig. lb further comprise a collimator 24, such as a CPC.

As shown in Pigs la- lb and other Pigures, the light guide has at least two ends, and extends in an axial direction between a first base surface (also indicated as first face 141) at one of the ends of the light guide and a second base surface (also indicated as second face 142) at another end of the light guide.

Reference 1100 refers to a light generating device comprising the light sources 10 and the elongated luminescent body 100, and optionally the light concentrating element 24. The light generating device has a radiation exit window 112 when there is no light concentrating element 24, and a radiation exit window 212 when there is a light

concentrating element 24.

The radiation exit window 112 is in optical contact, such as physical contact, with the light concentrating element 24, such as a CPC like light concentrating element (see also above). The CPC like) light concentrating element 24 has a radiation exit window 212.

In embodiments, however, the elongated luminescent body and light concentrating element are essentially a single (monolithic) body. Then, the radiation exit window 212 of the light concentrating element may essentially be the same as the radiation exit window 112 as there is essentially no physical boundary between the elongated luminescent body and the (CPC like) light concentrating element 24.

Fig. lc schematically depicts some embodiments of possible ceramic bodies or crystals as waveguides or luminescent concentrators. The faces are indicated with references 141-146. The first variant, a plate-like or beam-like light transmissive body has the faces 141-146. Light sources, which are not shown, may be arranged at one or more of the faces 143-146 (general indication of the edge faces is reference 147). The second variant is a tubular rod, with first and second faces 141 and 142, and a circumferential face 143. Light sources, not shown, may be arranged at one or more positions around the light transmissive body. Such light transmissive body will have a (substantially) circular or round cross-section. The third variant is substantially a combination of the two former variants, with two curved and two flat side faces. In the embodiment having a circular cross-section the number of side faces may be considered unlimited (¥).

In the context of the present application, a lateral surface of the light guide should be understood as the outer surface or face of the light guide along the extension thereof. For example in case the light guide would be in form of a cylinder, with the first base surface at one of the ends of the light guide being constituted by the bottom surface of the cylinder and the second base surface at the other end of the light guide being constituted by the top surface of the cylinder, the lateral surface is the side surface of the cylinder. Herein, a lateral surface is also indicated with the term edge faces or side 140.

The variants shown in Fig. lc are not limitative. More shapes are possible; i.e. for instance referred to W02006/054203, which is incorporated herein by reference. The ceramic bodies or crystals, which are used as light guides, generally may be rod shaped or bar shaped light guides comprising a height H, a width W, and a length L extending in mutually perpendicular directions and are in embodiments transparent, or transparent and luminescent. The light is guided generally in the length L direction. The height H is in embodiments < 10 mm, in other embodiments <5mm, in yet other embodiments < 2 mm. The width W is in embodiments < 10 mm, in other embodiments <5mm, in yet embodiments < 2 mm. The length L is in embodiments larger than the width W and the height H, in other embodiments at least 2 times the width W or 2 times the height H, in yet other embodiments at least 3 times the width W or 3 times the height H. Hence, the aspect ratio (of length/width) is especially larger than 1, such as equal to or larger than 2, such as at least 5, like even more especially in the range of 10-300, such as 10-100, like 10-60, like 10-20. Unless indicated otherwise, the term“aspect ratio” refers to the ratio length/width. Fig. lc schematically depicts an embodiment with four long side faces, of which e.g. two or four may be irradiated with light source light.

The aspect ratio of the height H : width W is typically 1 : 1 (for e.g. general light source applications) or 1 :2, 1 :3 or 1 :4 (for e.g. special light source applications such as headlamps) or 4:3, 16:10, 16:9 or 256:135 (for e.g. display applications). The light guides generally comprise a light input surface and a light exit surface which are not arranged in parallel planes, and in embodiments the light input surface is perpendicular to the light exit surface. In order to achieve a high brightness, concentrated, light output, the area of light exit surface may be smaller than the area of the light input surface. The light exit surface can have any shape, but is in an embodiment shaped as a square, rectangle, round, oval, triangle, pentagon, or hexagon.

Note that in all embodiments schematically depicted herein, the radiation exit window is especially configured perpendicular to the radiation input face(s). Hence, in embodiments the radiation exit window and radiation input face(s) are configured

perpendicular. In yet other embodiments, the radiation exit window may be configured relative to one or more radiation input faces with an angle smaller or larger than 90°.

Note that, in particular for embodiments using a laser light source to provide light source light, the radiation exit window might be configured opposite to the radiation input face(s), while the mirror 21 may consist of a mirror having a hole to allow the laser light to pass the mirror while converted light has a high probability to reflect at mirror 21. Alternatively or additionally, a mirror may comprise a dichroic mirror.

Fig. ld very schematically depicts a projector or projector device 2000 comprising the light generating system 1000 as defined herein. By way of example, here the projector 2000 comprises at least two light generating systems 1000, wherein a first light generating system lOOOa is configured to provide e.g. green light 101 and wherein a second light generating system lOOOb is configured to provide e.g. red light 101. Light source 10 is e.g. configured to provide blue light. These light sources may be used to provide the projection (light) 3. Note that the additional light source 10, configured to provide light source light 11 , is not necessarily the same light source as used for pumping the luminescent concentrator(s). Further, here the term“light source” may also refer to a plurality of different light sources. The projector device 2000 is an example of a light generating system 1000, which light generating system is especially configured to provide light generating system light 1001, which will especially include light generating system light 101.

High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection.

For this purpose, it is possible to make use of so-called luminescent concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. A rod of such a transparent luminescent material can be used and then it is illuminated by LEDs to produce longer wavelengths within the rod.

Converted light which will stay in the luminescent material such as a doped garnet in the waveguide mode and can then be extracted from one of the surfaces leading to an intensity gain (Fig. le).

High-brightness LED-based light source for beamer applications appear to be of relevance. For instance, the high brightness may be achieved by pumping a luminescent concentrator rod by a discrete set of external blue LEDs, whereupon the phosphor that is contained in the luminescent rod subsequently converts the blue photons into green or red photons. Due to the high refractive index of the luminescent rod host material (typically ~

1.8) the converted green or red photons are almost completely trapped inside the rod due to total internal reflection. At the exit facet of the rod the photons are extracted from the rod by means of some extraction optics, e.g. a compound parabolic concentrator (CPC), or a micro- refractive structure (micro-spheres or pyramidal structures). As a result, the high luminescent power that is generated inside the rod can be extracted at a relatively small exit facet, giving rise to a high source brightness, enabling (1) smaller optical projection architectures and (2) lower cost of the various components because these can be made smaller (in particular the, relatively expensive, projection display panel).

Fig. lf schematically depicts an embodiment of a luminaire or light generating system 1000 (or other type of lighting device) comprising the light generating system 1000. The luminaire 1000 provide light which may - in a control mode of the luminaire - comprise the lighting generating system light 1001. Figs. 2a-2b schematically depict embodiments of a light generating system 1000 comprising a light source 10 configured to provide light source light 11 and an elongated luminescent body 100 having a length L (see Fig. 2b).

As indicated above, the elongated luminescent body 100 comprises (n) side faces 140, here 4, over at least part of the length. The (n) side faces 140 comprise a first side face 143, comprising a radiation input face 111, and a second side face 144 configured parallel to the first side face 143, wherein the side faces 143, 144 define a height h.

As indicated above, the elongated luminescent body 100 further comprises a radiation exit window bridging at least part of the height h between the first side face 143 and the second side face 144 (see especially Fig. la). The luminescent body 100 comprises a garnet type A3B5O12 luminescent material 120 comprising trivalent cerium, wherein the garnet type A3B5O12 luminescent material 120 is configured to convert at least part of the light source light 11 into converter light 101.

Further, the light generating system 1000 comprises one or more heat transfer elements 200 in thermal contact with one or more side faces 140 and a reflector 2100 configured at the second side face 144 and configured to reflect light source light 11 escaping from the elongated luminescent body 100 via second face 144 back into the elongated luminescent body 100.

The one or more heat transfer elements 200 are especially configured parallel to at least part of one or more of the side faces 140 over at least part of the length of the elongated luminescent body 100 at a shortest distance (dl) from the respective one or more side faces 140. The shortest distance dl is especially 1 pm < dl < 100 pm.

As shown in Figs. 2a-2b, the one or more heat transfer elements 200 comprise one or more heat transfer element faces 201 directed to one or more side faces 140. As shown in these schematic drawings, the one or more heat transfer elements 200 are at least in thermal contact with all side faces 140 other than the first side face 143. Further, as also shown in these schematic drawings, the one or more heat transfer elements 200 may be configured as a monolithic heat transfer element 220. In embodiments, this monolithic heat transfer element 220 is configured in thermal contact with a support 240 for the light source 10.

A heat transfer element face 201 of the one or more heat transfer element 200 directed to the second face 144 comprises the reflector 2100. Here, all faces 201 directed to the luminescent body 100 comprise such reflector 2100. Fig. 2b schematically depict another embodiment of the monolithic heat transfer element 220, including a slit 205 configured to host the luminescent body 100. The light sources 10 may be provided as LED bar. The monolithic heat transfer element 220 is used for cooling of the luminescent body 100.

The optional intermediate plate, indicated with reference 250, may serve as a spacer to keep the luminescent body at the desired distance from the light sources and may also serve as a reflector for the light that escapes from the luminescent body side faces. As an alternative, the spacer could be integrated with the one or more heat transfer element 200, especially a top one or more heat transfer element 200 (such as a top cooling block).

In Figs. 2a-2b, the one or more heat transfer elements are configured within a circle section of at least 180°, here in fact about 270°.

As shown above, the light generating system 1000 comprises in embodiments a plurality of light sources 10 configured to provide light source light 11 and an elongated luminescent body 100 comprising one or more side faces 140, the elongated luminescent body 100 comprising a radiation input face 111 and a radiation exit window 112, wherein the radiation input face 111 is configured in a light receiving relationship with the plurality of light sources 10, wherein the elongated luminescent body 100 comprises luminescent material 120 configured to convert at least part of light source light 11 (received at the radiation input face 111) into luminescent material light 8.

Fig. 3a schematically depicts an embodiment of a lateral displacement polarizing beam splitter 300. As schematically shown, the lateral displacement of the lateral displacement polarizing beam splitter 300 is configured in a direction parallel to the height Hl of the radiation exit window (see further below). Reference RP refers to the (two) rhombohedric prisms. Reference PBSC refers to a PBS coating. Reference WP refers to a half wave plate. In this way, from a single beam of unpolarized system light 101 two beams of polarized light are generated, having the same polarization, and laterally displaced relative to each other with lateral displacement ld. Reference 310 refers to a lateral displacement polarizing beam splitter element. As shown, the lateral displacement polarizing beam splitter 300 comprises an array of lateral displacement polarizing beam splitter elements 310.

Reference 351 refers to (an optional) reflective element or attenuation element, which blocks light. For instance, this may be a metal layer.

Fig. 3b schematically depicts an embodiment of the light generating system 100. Reference 01 refers to a condenser or collimations lens, which is especially used to collimate the light from the HFD module i.e. make a (more or less) parallel beam in order to facilitate/optimize optical propagation of the light through the optical system; reference 02 refers to a relay lens, which is especially used to optimize light guiding and light relaying; and reference 03 refers to a field lens which is especially used to ensure that the light hits the LCD panel at the most favorable way, e.g. to increase the contrast ratio between black/white pixels. References FE1 and FE2 refer to fly eye lenses.

With reference to Figs. 3a and 3b, Fig. 3b schematically depicts an embodiment wherein the lateral displacement polarizing beam splitter 300 comprises an array of lateral displacement polarizing beam splitter elements 310. The one or more fly eye lenses FEl,FE2 are configured to focus the luminescent material light on the respective lateral displacement polarizing beam splitter elements 310.

Fig. 3c schematically depicts a light generating system 1000. The light generating system 1000 comprises a plurality of light sources 10 configured to provide light source light 11. The system 1000 further comprises an elongated luminescent body 100 comprising one or more side faces 140, the elongated luminescent body 100 comprising a radiation input face 111 and a radiation exit window 112 (or 212). The radiation input face 111 is configured in a light receiving relationship with the plurality of light sources 10. The elongated luminescent body 100 comprises luminescent material configured to convert at least part of light source light 11 into luminescent material light 8.

The radiation exit window 112,212 has a height H and a width W, defining a first aspect ratio ARl=Wl/Hl.

The light generating system 1000 also comprises a lateral displacement polarizing beam splitter 300 configured in a light receiving relationship with the radiation exit window 112,212 of the elongated luminescent body 100. As very schematically shown, the lateral displacement, indicated with reference ld, of the lateral displacement polarizing beam splitter 300 is configured in a direction parallel to the height H of the elongated luminescent body 100.

The light generating system 1000 may comprise an LCD panel 400. Hence, Fig. 3c also very schematically depicts a projector system, only including the relevant elements for understanding the present invention. Hence, this embodiments also includes a liquid crystal panel 400 having a second height H2 and a second width W2 defining a second aspect ratio AR2=W2/H2. As schematically shown, the liquid crystal panel 400 is configured downstream of the lateral displacement polarizing beam splitter 300. Further, as can be derived from this drawing, ARl>AR2. As schematically depicted in Fig. 3c, especially in the present invention the width Wl of the radiation exit window and the width W2 of the LCD are configured essentially parallel (likewise the heights Hl and H2 may be configured essentially parallel).

Referring to 3d, herein especially the first aspect ratio AR1 is of the radiation exit window 112 of the elongated luminescent body 100.

Fig. 3e schematically depicts the same embodiment as schematically depicted in Fig. 3d, but now with downstream of the elongated luminescent body 100 a light concentration element configured. In general, the aspect ratio of the light concentrating element 24, such as a CPC like light concentrating element, is essentially the same as the aspect ratio of the elongated luminescent body 100. However, would there be a difference, AR1 may then refer to the aspect ratio of the radiation exit window 212 (see Fig. lb).

Figs. 3d and 3e also schematically depicts an embodiment wherein the plurality of light sources 10 is configured in a 2D array. Here, schematically two rows are depicted. However, more than two rows may also be available in embodiments.

Systems where simulated, amongst others with a rod for DLP with dimensions 1.20* 1.90 mm ² , leading to an area of 2.280mm ² . The etendue E=2.280*(1.52) ² *p =16.5 for a luminescent elongated body and CPC with n=l .52. In an alternative embodiment, with an aspect ratio of the LCD of AR2=l .60, a rod with ARl=l .30 for LCD DLP of 1.20* 1.56 mm ² , leading to an area of 1.872mm ² . The etendue E=1.872*(1.52) ² *p =13.6 for an elongated luminescent body and CPC with n=l .52. For LCD based projectors with an LCD panel with an aspect ratio of 1.3, a luminescent elongated body with an aspect ratio of 1.6 can be used in combination with a lateral displacement polarizing beam splitter with a displacement in the direction of the width, see also the values in italic below.

However, when the lateral displacement is in the direction of the height, following results may be obtained:

Fig. 4 schematically also depicts an embodiment of the projector system 200. Reference Ml refers to a dichroic mirror, which separates the luminescent material light in two colors, such as red and green, which follow at least partially different optical pathways. One color is transmitted through the dichroic mirror and is directed to the respective LCD panel 400, here especially indicated as LCD panel 402 in order to distinguish over other LDC panels, via optics, such as a mirror M2 and a mirror M3. Another color is reflected at the dichroic mirror Ml, and is directed to the respective LCD panel 400, here especially indicated as LCD panel 401. The other color, such as blue light, may be provided directly with light sources 1010, which may essentially be identical to light sources 10 of the light generating system 1000. In order to distinguish from the pump light sources 10, these light sources are indicated with reference 1010.

The light that is directed to the LCD panels 400 may be transmitted via a micro lens array MLA. In this way, the system may be more efficient as light may not impinge on borders between different LCD pixels. This is known in the art. Reference 500 refers to an integrator or dichroic X-cross or dichroic combiner prism. Further optics than schematically depicted may also be available.

More optical elements than depicted herein may be comprised by the system(s).

The term“plurality” refers to two or more.

The terms“substantially” or“essentially” herein, and similar terms, will be understood by the person skilled in the art. The terms“substantially” or“essentially” may also include embodiments with“entirely”,“completely”,“all”, etc. Hence, in embodiments the adjective substantially or essentially may also be removed. Where applicable, the term “substantially” or the term“essentially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, even more especially 99.5% or higher, including 100%.

The term“comprise” includes also embodiments wherein the term “comprises” means“consists of’.

The term“and/or” especially relates to one or more of the items mentioned before and after“and/or”. For instance, a phrase“item 1 and/or item 2” and similar phrases may relate to one or more of item 1 and item 2. The term "comprising" may in an

embodiment refer to "consisting of' but may in another embodiment also refer to "containing at least the defined species and optionally one or more other species".

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The devices, apparatus, or systems may herein amongst others be described during operation. As will be clear to the person skilled in the art, the invention is not limited to methods of operation, or devices, apparatus, or systems in operation.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words“comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.

The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a device claim, or an apparatus claim, or a system claim, enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The invention also provides a control system that may control the device, apparatus, or system, or that may execute the herein described method or process. Yet further, the invention also provides a computer program product, when running on a computer which is functionally coupled to or comprised by the device, apparatus, or system, controls one or more controllable elements of such device, apparatus, or system.

The invention further applies to a device, apparatus, or system comprising one or more of the characterizing features described in the description and/or shown in the attached drawings. The invention further pertains to a method or process comprising one or more of the characterizing features described in the description and/or shown in the attached drawings.

The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined. Furthermore, some of the features can form the basis for one or more divisional applications.