FIELD OF THE INVENTION

The invention relates to a luminescent concentrator and to a projection system or a luminaire comprising such luminescent concentrator.

BACKGROUND OF THE INVENTION

Luminescent concentrators are known in the art. WO2015/113979A, for instance, describes a light emitting device comprising at least one light source adapted for, in operation, emitting first light with a first spectral distribution, a light guide made of a luminescent material and comprising a light input surface and a light exit surface extending in an angle different from zero to one another, the light guide further comprising a first further surface extending parallel to and arranged opposite to the light exit surface, wherein the light guide is adapted for receiving the first light with the first spectral distribution at the light input surface, converting at least a part of the first light with the first spectral distribution to second light with a second spectral distribution, guiding the second light with the second spectral distribution to the light exit surface and coupling the second light with the second spectral distribution out of the light exit surface. The light emitting device further comprises a phosphor element arranged adjacent to the first further surface and a reflective element arranged adjacent the phosphor element opposite to the first further surface. The phosphor element is adapted for converting light incident from the light guide to third light with a third spectral distribution and the light guide is furthermore adapted for receiving the third light with the third spectral distribution at the first further surface, guiding the third light with the third spectral distribution to the light exit surface and coupling the third light with the third spectral distribution out of the light exit surface.

SUMMARY OF THE INVENTION

Luminescent concentrators for HLD light sources have been developed over the past few years. HLD (high lumen density) technology is a new LED-based light-source technology that may e.g. used for digital projection. Amongst others, a transparent ceramic luminescent rod may be used that is pumped by arrays of e.g. blue LEDs. A substantial part of the light generated inside the rod is reflected at the rod surface by total internal reflection (TIR) and guided towards the ‘nose’ sides of the rod. At the back side of the luminescent rod a reflector can be placed to send the light back towards the opposite side of the rod where the light is extracted e.g. by a compound parabolic concentrator (CPC). In embodiments, for the rod material a cerium- doped (lutetium and/or or yttrium-based) garnet material may be used, which can be single- crystalline or poly crystalline. Double-sided irradiance configurations or single-sided irradiance configurations may be applied. Especially, the rod may have a rectangular cross- sectional shape, though other shapes, like a circular cross-sectional shape may also be possible.

Assuming a cerium doped garnet based solution, an HLD light source may predominantly emit the converted light from the luminescent conversion material in the yellow-green spectral wavelength range. For many applications, a light source is requested or preferred that emits white light, or light with a broader spectrum. This concerns both general lighting applications as well as e.g. light engines for e.g. LCD projection systems. In the latter case, this may be based on the engines that have been developed for discharge lamps and of which the architecture and components or building blocks are preferred to be re-used.

With the HLD light sources, externally one or more other colors can be mixed dichroically, for instance for a DLP projection system. However, this may require a relatively large additional volume and additional optical components and may also essentially only be applicable for spectrally well separated beams. The latter means that any spectral overlap of the beams that are to be mixed may result in additional optical losses.

Hence, it is an aspect of the invention to provide an alternative light generating device, which preferably further at least partly obviates one or more of above-described drawbacks. 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.

Amongst others, it is herein in embodiments proposed to provide a composite spectrum that comprises the converted light as emitted from the luminescent conversion material, as well as laser radiation from one or more laser diodes (LDs) that is mixed in the optical path of the HLD module, resulting in an output spectrum with reduced saturation, and/or a broader spectral emission, enabling e.g. white light emitting light engines or engines with bi- or multi-modal band emission for increased color gamut light sources. Amongst others, in this way compact a high brightness light source can be realized, without the need for external dichroic mixing of separately collimated light of different spectral content and that enable overlapping spectra of the luminescent emission and the laser diode light.

Hence, in a first aspect the invention provides a light generating device (“lighting device” or “device”) comprising a plurality of first light sources, a light emitting structure, and a second light source. Especially, the plurality of first light sources are configured to provide first light source light, especially UV and/or blue first light source light. Further, especially the light emitting structure may have a structure length (LI) defined by a first structure face and a second structure face, wherein the second structure face comprises a structure radiation exit window. In specific embodiments, the light emitting structure comprises an elongated light transmissive body, wherein the elongated light transmissive body has a body length (L2), defined by a first body face and a second body face. Even more especially, in embodiments the first body face and the first structure face coincide. Further, in specific embodiments L1>L2. Especially, the elongated light transmissive body further comprises one or more side faces, wherein the one or more side faces comprise a radiation input face configured in a light receiving relationship with the plurality of first light sources. Further, especially the elongated light transmissive body comprises a luminescent material configured to convert at least part of first light source light into luminescent material light. In specific embodiments, during operation of the plurality of light sources at least part of the luminescent material light escapes from the structure radiation exit window. Further, in embodiments the second light source is configured to generate second light source light, such as blue or red. In specific embodiments, the second light source comprises a laser light source. Further, especially the second light source in combination with an optical redirection element (“redirection element”), is configured to provide the second light source light to an incoupling position (P) between the first structure face and the second structure face. More especially, the second light source, in combination with an optical redirection element, is configured to provide the second light source light to an incoupling position (P) at one or more of the one or more side faces, under a first angle (b) with a normal (to the respective side face where the second light source light is coupled into the elongated light transmissive body) unequal to 0°. Hence, especially in this way after incoupling (such as in the elongated light transmissive body) the second light source light propagates in a direction of the structure radiation exit window. The incoupling position (P) is at distance from the first structure face of more than 0.5*L2. Hence, especially the invention provides a light generating device comprising a plurality of first light sources, a light emitting structure, and a second light source, wherein: (a) the plurality of first light sources are configured to provide first light source light; (b) the light emitting structure has a structure length (LI) defined by a first structure face and a second structure face, wherein the second structure face comprises a structure radiation exit window, wherein the light emitting structure comprises an elongated light transmissive body, wherein the elongated light transmissive body has a body length (L2), defined by a first body face and a second body face, wherein the first body face and the first structure face coincide, wherein L1>L2, wherein the elongated light transmissive body further comprises one or more side faces, wherein the one or more side faces comprise a radiation input face configured in a light receiving relationship with the plurality of first light sources, wherein the elongated light transmissive body comprises a luminescent material configured to convert at least part of first light source light into luminescent material light, wherein during operation of the plurality of light sources at least part of the luminescent material light escapes from the structure radiation exit window; (c) the second light source is configured to generate second light source light, wherein the second light source comprises a laser light source, wherein the second light source in combination with an optical redirection element, is configured to provide the second light source light to an incoupling position (P) between the first structure face and the second structure face (especially at one or more of the one or more side faces) under a first angle (b) with a normal (to the respective side face where the second light source light is coupled into the elongated light transmissive body) unequal to 0° such that after incoupling (especially in the elongated light transmissive body) the second light source light propagates in a direction of the structure radiation exit window; and wherein the incoupling position (P) is at distance from the first structure face of more than 0.5*L2. The optical redirection element comprises one or more of a mirror and/or a redirection element, wherein the redirection element is optically coupled with the light emitting structure. Particularly, the one or more sides faces of the elongated light transmissive body, and the first and/or second body face are positioned relative to each other at an angle unequal to zero degrees and unequal to 180 degrees. In an embodiment, the one or more sides faces of the elongated light transmissive body, and the first and/or second body face are positioned relative to each other at an angle of 90 degrees.

As indicated above, this may provide device light with an increased color gamut. Further, in this way a compact high brightness light source can be realized without the need for external dichroic mixing of separately collimated light of different spectral content and/or that may (but not necessarily) enable in embodiments overlapping spectra of the luminescent emission and the second light source light. Further, with the present invention in embodiments white light may generated with e.g. a variable correlated color temperature, color rendering index, and/or color point.

Hence, in specific embodiments the light generating device may be configured to generate white device light in one or more operational modes of the light generating device. In further specific embodiment, the white device light comprises the luminescent material light and one or more of the first light source light and the second light source light (see further also below). 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 1800 K and 20000 K, such as between 2000 and 20000 K, especially 2700-20000 K, for general lighting especially in the range of about 2700 K and 6500 K. In embodiments, for backlighting purposes the correlated color temperature (CCT) may especially be in the range of about 7000 K and 20000 K. Yet further, in embodiments the correlated color temperature (CCT) is 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.

In one or more operation modes, the device light has a total spectral power (in Watt) of which in the range of 2-80% of the total spectral power is provided by the second light source light, like at least 4%. When e.g. only blue or red is added, the contribution may e.g. be in the range of 2-50%. However, when two or more different colors are added, the contribution may be even up to about 80%, such as up to about 75%. In other operational modes, the second light source light may not be available in the device light, dependent upon the desired spectral distribution of the device light.

As indicated above, the light generating device comprises a plurality of first light sources, a light emitting structure, and a second light source.

Hence, the light generating device comprises first light sources and one or more second light sources. Here, the term “light source” is further elucidated in general, with respect to the first light source or the second light source. The term “light source” may refer to a semiconductor light-emitting device, such as a light emitting diode (LEDs), a resonant cavity light emitting diode (RCLED), a vertical cavity laser diode (VCSELs), an edge emitting laser, etc.. The term “light source” may also refer to an organic light-emitting diode, such as a passive-matrix (PMOLED) or an active-matrix (AMOLED). In a specific embodiment, the light source comprises a solid state light source (such as a LED or laser diode). In an embodiment, the light source comprises a LED (light emitting diode). The term LED may also refer to a plurality of LEDs. 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. 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 term “light source” may also relate to a plurality of (essentially identical (or different)) light sources, such as 2-2000 solid state light sources. In embodiments, the light source may comprise one or more micro-optical elements (array of micro lenses) downstream of a single solid state light source, such as a LED, or downstream of a plurality of solid state light sources (i.e. e.g. shared by multiple LEDs). In embodiments, the light source may comprise a LED with on- chip optics. In embodiments, the light source comprises a pixelated single LEDs (with or without optics) (offering in embodiments on-chip beam steering). The phrases “different light sources” or “a plurality of different light sources”, and similar phrases, may in embodiments refer to a plurality of solid state light sources selected from at least two different bins. Likewise, the phrases “identical light sources” or “a plurality of same light sources”, and similar phrases, may in embodiments refer to a plurality of solid state light sources selected from the same bin.

The first light sources are essentially used to pump the luminescent material (see further below). The first light source light may essentially be absorbed by the luminescent material, and not escape from the light generating device. However, in other embodiments at least part of the first light source light is not absorbed (by the luminescent material), and may escape from the light generating device. The first light sources are thus especially solid state light sources. For instance, the first light sources may be LEDs. The first light source may especially be configured to generate one or more of UV and blue radiation. The plurality of first light sources are configured to provide first light source light; see further also below.

The second light source is especially configured to generate second light source light. In embodiments this may be blue second light source light. In other embodiments this may be green second light source light. In yet other embodiments this may be yellow second light source light. In yet further embodiments this may be amber second light source light. In yet further embodiments this may be orange second light source light. In other embodiments this may be red second light source light. In specific embodiments, a plurality of second light sources may be applied wherein a first subset of one or more second light sources is configured to generate a first type of second light source light and a second subset of one or more second light sources is configured to generate a second type of second light source light. The first type and the second type of second light source light may have different spectral power distributions. In specific embodiments, the respective color points of the first type and the second type of second light source may differ with at least 0.01 for u’ and/or with least 0.01 for v’, even more especially at least 0.02 for u’ and/or with least 0.02 for v’. In yet more specific embodiments, the respective color points of first type and the second type of second light source may differ with at least 0.03 for u’ and/or with least 0.03 for v’. Here, u’ and v’ are color coordinate of the light in the CIE 1976 UCS (uniform chromaticity scale) diagram. As in embodiments the luminescent material light may have a color point in the yellow-green spectral range, especially the second light source light may be blue second light source light, e.g. to provide white light or white light with a higher correlated color temperature (CCT), or may be red second light source light, e.g. to provide white light or white light with a lower correlated color temperature. Hence, in specific embodiments the second light source light comprises blue light source light, or the second light source light comprises red light source light, or a plurality of second light sources is applied wherein a first subset of one or more second light sources is configured to generate blue second light source light and a second subset of one or more second light sources is configured to generate red second light source light. However, instead of red second light source light, or in addition to red second light source light, also amber and/or orange second light source light may be provided.

As indicated above, especially the second light source(s) is (are) (a) laser light source(s). Hence, especially the second light source light is laser light source light (like a laser diode (LD)). When a plurality of second (laser) light sources are applied, the laser light sources may be arranged in a laser bank. The laser bank may in embodiments comprise heat sinking and/or optics e.g. a lens to collimate the laser light. A laser bank may e.g. comprise at least 10, such as at least 20 laser light sources.

The light generating device further comprises the light emitting structure. The term “the light emitting structure” is applied, as under irradiation with the first light source light of at least part of the light emitting structure, luminescent material light may be generated, whereby the structure is (thus) a light emitting structure. The term “structure” is applied, as the light emitting structure may consist of more than one element. However, in specific embodiments the light emitting structure may also consist of a single element. Especially, the light emitting structure comprises at least an elongated light transmissive body which comprises a luminescent material. As the elongated light transmissive body comprises a luminescent material, the elongated light transmissive body may also be indicated as “elongated luminescent body” or “luminescent body”. Further, the light emitting structure may comprise an optical element configured to facilitate extraction, homogenize, and/or collimate the (luminescent material) light escaping from the elongated light transmissive body. Further, the light emitting structure may comprise an optical coupling material between the elongated light transmissive body and the optical element. However, the elongated light transmissive body and the optical element may in embodiments also be a monolithic body. In alternative embodiments, the light emitting structure may comprise an intermediate non-luminescent body, configured downstream of the elongated light transmissive body and upstream of the optional optical element.

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”.

The light emitting structure has a structure length (LI) defined by a first structure face and a second structure face. Especially, the second structure face comprises a structure radiation exit window. The device light may especially comprise the light that may escape from the radiation exit window. In embodiments, the radiation exit window is a window of the elongated light transmissive body. In yet other embodiments, the radiation exit window is a window of the optical element (as indicated above). Especially, the first structure face is a face of the elongated light transmissive body (see also below).

As already indicated above, especially the light emitting structure comprises an elongated light transmissive body. Especially, the elongated light transmissive body has a body length (L2), defined by a first body face and a second body face. Further, as indicated above, the first body face and the first structure face coincide.

As may be clear from the above, especially L1>L2. In embodiments wherein L1=L2, the light emitting structure may essentially consist of the elongated light transmissive body. In specific embodiments, L1<5*L2, such as L1<3*L2, like L1<2*L2.

Especially, the elongated light transmissive body further comprises one or more side faces. The one or more side faces comprise a radiation input face configured in a light receiving relationship with the plurality of first light sources. The one or more side faces may also comprise a plurality of radiation input faces, such as in embodiments wherein illumination from two sides is applied.

As indicated above, the elongated light transmissive body comprises a luminescent material configured to convert at least part of first light source light into luminescent material light. Hence, during operation of the plurality of light sources at least part of the luminescent material light escapes from the structure radiation exit window. This may in embodiments be colored light. In yet other embodiments, this may be white light. In yet further embodiments, the spectral distribution of the device light may be controllable (see also below). During operation of the plurality of light sources luminescent material is generated in the elongated light transmissive body. At least part of the luminescent material light may escape from the radiation exit window, which may be comprised by the second body face (which may also be indicted as “nose”). Downstream of the elongated light transmissive body the optical element may be configured, which has a radiation exit window. Hence, during operation of the plurality of light sources at least part of the luminescent material light escapes from the light emitting structure via the structure radiation exit window.

It appears beneficial for the efficiency of the device when the second light source light is provided to the light emitting structure, especially the elongated light transmissive body, closer to the second end than to the first end. It appears that the smaller the optical path of the second light source light through material, especially through material of the elongated light transmissive body, the less second light source light may escape from the second structure face. This may be due to multiple total internal reflections and/or absorption and/or scattering by the material through which it propagates. Hence, especially the second light source light is provided such, that its direction is to the second structure face. Therefore, where the first light sources may in general be configured such that the first light source light is essentially perpendicular to the radiation input face, the second light source light may enter the light emitting structure, especially the elongated light transmissive body, under an angle unequal to 90° (with a face of the light emitting structure where the second light source light is coupled into the light emitting structure). Hence, the optical axis when entering the light emitting structure, especially the elongated light transmissive body, may have an angle with a normal to a body axis of the light emitting structure unequal to 0°. This may be obtained by positioning the second light source light such that the second light source light irradiates a surface of the light emitting structure, such as a side face of the elongated light transmissive body, with the desired angle. Alternatively or additionally, an optical redirection element, such as a mirror, may be applied to create the desired angle (see also below). The term “optical redirection element” may also refer to a plurality of (different) optical redirection elements. The redirection element may comprise a mirror. Alternatively or additionally, the redirection element may comprise a prismatic structure. The redirection element may be configured in optical contact with the elongated light transmissive body or may be configured at some distance thereof, in order to prevent optical contact. The optical redirection element is, however, optically coupled (or radiatively coupled) with the elongated light transmissive body.

Hence, the second light source in combination with an optical redirection element, is configured to provide the second light source light to an incoupling position (P) between the first structure face and the second structure face (especially at one or more of the one or more side faces) under a first angle (b) with a normal unequal to 0° such that after incoupling (especially in the elongated light transmissive body) the second light source light propagates in a direction of the structure radiation exit window. It appears desirable that the incoupling position (P) is at distance from the first structure face of more than 0.5*L2. When two or more second light sources are applied, there may be one or more incoupling positions. For each incoupling position applies that distance from the first structure face of more than 0.5*L2. Hence, assuming incoupling via the elongated light transmissive body, in the halve of the elongated light transmissive body most remote of the first end face, the second light source light is coupled in, especially with a direction to the second end face.

Hence, in embodiments an optical element may be used to provide the desired angle. In specific embodiments, the optical redirection element may comprise one or more of a mirror and a redirection element. In embodiments the redirection element is optically coupled with the elongated light transmissive body. The mirror is especially a specular mirror. The optical element may e.g. be a relatively small shaped light transparent body, such as a wedge-shaped body. Such body may provide via refraction or via internal reflection the desired angle. Especially, the redirection element is non-luminescent. Further, especially the redirection element is optically coupled with the light emitting structure, especially the elongated light transmissive body.

In order to promote incoupling of the light, an antireflective coating may be applied. This may apply to the (part of the) face wherein first light source light is coupled into the elongated light transmissive body. Alternatively or additionally, this may apply to the (part of the) face wherein second light source light is coupled into the elongated light transmissive body. Hence, in specific embodiments the light generating device may further comprise an anti-reflective coating configured downstream of the second light source and upstream of the elongated light transmissive body.

Further, it appears that especially efficient results may be applied when the second light source light is polarized and further especially has a specific first angle. Hence, in embodiments the second light source light is p polarized with respect to the elongated light transmissive body. To this end, e.g. a polarizer may be applied. As indicated above, especially the second light source may be a laser light source. Hence, especially the second light source light is polarized second laser light source light, even more especially p- polarized second laser light source light. In general, a laser produces partly polarized light; so in embodiments the laser is oriented in such a way that it is p polarized with respect to the elongated light transmissive body. The polarization direction (i.e. the direction of the p- polarization) is especially in a plane containing an optical axis of the second light source light and a normal to a surface of incidence of the second light source light (on e.g. the elongated light transmissive body).

Most efficient incoupling may be obtained when the first angle is essentially the Brewster angle. Hence, in embodiments the first angle (b) is in the range of the Brewster angle ± 5°, such as in the range of the Brewster angle ± 2°. The Brewster angle relates to the second light source light wavelength and the index of refraction of the material where the second light source light is being coupled in, such as the index of refraction of the elongated light transmissive body.

Especially, the elongated light transmissive body has a length (L2) along a body axis (BA) and a cross-section (A2) perpendicular to the body axis (BA). In specific embodiments, the cross-section has an equivalent circular diameter D2, wherein L2>2*D2, especially wherein L2>5*D2, especially L2>10*D2. The equivalent circular diameter (or ECD) of an (irregularly shaped) two-dimensional shape is the diameter of a circle of equivalent area. For instance, the equivalent circular diameter of a square with side a is 2*a*SQRT(l/t). The larger the ratio L2/D2, the larger the radiation input face may be.

Especially, the second light source light may be coupled into the elongated light transmissive body. More especially, in such embodiments the second light source light may be coupled into the elongated light transmissive body relatively close to the second end / relatively far from the first end. Hence, in embodiments the elongated light transmissive body has a second dimension (D22), perpendicular to the body length (L2) and selected from a body height (H2) and a body diameter (D2), wherein L2>10*D22, wherein the incoupling position (P) is within an incoupling distance Lp of 3*D22 from the second body face. Even more especially, the incoupling distance Lp is selected from the range of 0.6*D22 - 1.0*D22. In yet more specific embodiments, D22 is a body height (H2) of the elongated light transmissive body. In general, the body height is smaller than the body width. Hence, in embodiments wherein the cross-section is rectangular, e.g. W2>2*H2, such as W2>5*H2. Note that especially the length is at least 5 times larger than the largest second dimension (see above).

Therefore, in embodiments the elongated light transmissive body has a rectangular cross-section with a body width (W2) and body height (H2) as second dimensions (D22), wherein W2>H2, wherein the plurality of light sources are configured to provide the first light source light to one or more side faces having the body width (W2), and wherein the second light source is configured to provide the second light source light to one or more side faces having the body height (H2). Hence, in embodiments the first light sources may be configured to irradiate a side face defined by L2 and W2, i.e. a larger side face, and the second light source may be configured to irradiate a smaller side face, a side face defined by L2 and H2.

Note however, that other embodiments may also be possible. For instance, in embodiments the first light sources may be configured to irradiate a single larger side face (single sided irradiation) or may be configured to irradiate two larger side faces (double sided irradiation). In yet other embodiments, the first light sources may be configured to irradiate a single smaller side face (single sided irradiation) or may be configured to irradiate two smaller side faces (double sided irradiation). In yet further embodiments the first light sources may be configured to irradiate a single larger side face (single sided irradiation) or may be configured to irradiate two larger side faces (double sided irradiation), and the second light sources may be configured to irradiate a single larger side face (single sided irradiation) or may be configured to irradiate two larger side faces (double sided irradiation). In yet other embodiments the first light sources may be configured to irradiate a single smaller side face (single sided irradiation) or may be configured to irradiate two smaller side faces (double sided irradiation), and the second light sources may be configured to irradiate a single smaller side face (single sided irradiation) or may be configured to irradiate two smaller side faces (double sided irradiation). Further, as indicated above the term “light source” may also refer to a plurality of light sources. Hence, in embodiments there may also be a plurality of second light sources configured to irradiated one or more of the side faces.

Especially suitable luminescent materials are cerium comprising garnet materials. Embodiments of garnets especially include A3B5O12 garnets, wherein A comprises at least yttrium or lutetium and wherein B comprises at least aluminum. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium; especially however with Ce. 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 (i.e. the B 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. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu).

Further, Gd and/or Tb are especially only present up to an amount of about 20% of A. In a specific embodiment, the garnet luminescent material comprises (Yi- _x Lu _x ^BsO iCe, wherein x is equal to or larger than 0 and equal to or smaller than 1. The term “:Ce”, indicates that part of the metal ions (i.e. in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Yi- _x Lu _x ^ALO iCe, part of Y and/or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10%; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2% (relative to A). Assuming 1% Ce and 10% Y, the full correct formula could be (Yo _.i Luo _. ssiCeo _. oi^AbO . Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art. In specific embodiments the luminescent material comprises (Y _xi-x2-x3 A _X2 Ce _x3 ) ₃ (Al _yi-y2 B _y2 ) ₅ 0i ₂ , wherein xl+x2+x3=l, wherein x3>0, wherein 0<x2+x3<0.2, wherein y 1 +y 2=1, wherein 0<y2<0.2, wherein A comprises one or more elements selected from the group consisting of lanthanides and scandium, and wherein B comprises one or more elements selected from the group consisting of Ga and In, wherein in specific embodiments at maximum 10% of Al-0 may be replaced by Si-N. As indicated above, in specific embodiments x3 is selected from the range of 0.001-0.04. Especially such luminescent materials may have a suitable spectral distribution (see however below), have a relatively high efficiency, have a relatively high thermal stability, and allow a high CRI (in combination with the first light source light and the second light source light (and the optical filter)). Hence, in specific embodiments A may be selected from the group consisting of Lu and Gd. Alternatively or additionally, B may comprise Ga. Hence, in embodiments the luminescent material comprises (Yxi-x2-x3(Lu,Gd)x2Cex3)3(Al _yi -y2Ga _y2 )50i2, wherein Lu and/or Gd may be available. Even more especially, x3 is selected from the range of 0.001-0.1, wherein 0<x2+x3<0.1, and wherein 0<y2<0.1. Further, in specific embodiments, at maximum 1% of Al-0 may be replaced by Si-N. Here, the percentage refers to moles (as known in the art); see e.g. also EP3149108. In yet further specific embodiments, the luminescent material comprises (Yxi-x3Ce _X3 )3Al50i2, wherein xl+x3=l, and wherein 0<x3<0.2, such as 0.001-0.1. In specific embodiments, the light generating device may only include luminescent materials selected from the type of cerium comprising garnets. In even further specific embodiments, the light generating device includes a single type of luminescent materials, such as (Yxi-x2-x3A _X2 Cex3)3(Al _yi -y2By2)50i2.

Further, in specific embodiments the light emitting structure may be chosen such, that part thereof, especially a light transmissive part, comprises the luminescent material, and another part thereof, especially also a light transmissive part, does not comprise the luminescent material. In such embodiments, the second light source light may be introduced in the part that does not comprise the luminescent material. Such part may be an optical element, such as a CPC like element, or an extension of the elongated light transmissive body, or even part of the elongated light transmissive body. In general, the optical element may not (substantially) comprise a light absorbing material, such as the luminescent material. The luminescent material absorbs at least part of the first light source light. Likewise, an extension of the elongated light transmissive body may not (substantially) comprise a light absorbing material, such as the luminescent material. However, the luminescent material may also be inhomogeneously distributed within the elongated light transmissive body. In such embodiments, the second light source light may be introduced in part of the elongated light transmissive body which may have a reduced or essentially zero luminescent material content. This may also be the case with ceramic bodies, wherein e.g. the cerium content may be higher over a first part of the length and smaller or substantially zero over another part of the length.

Hence, in specific embodiments the elongated light transmissive body has an inhomogeneous distribution of the luminescent material, wherein a first concentration cl of the luminescent material in the elongated light transmissive body between the first body face and the incoupling position (P) is higher than a second concentration c2 of the luminescent material in the elongated light transmissive body between the incoupling position (P) and the second structure face. For instance, in embodiments a concentration of the luminescent material in the elongated light transmissive body between the first body face and the incoupling position (P) may be higher than a concentration of the luminescent material in the elongated light transmissive body between the incoupling position (P) and the second body face. A ratio of the concentrations, of the lower relative to the higher may be at maximum 0.5, such as at maximum 0.2, like especially at maximum 0.1, like even more especially at maximum 0.01, like even more especially at maximum 0.001. Even more especially, in embodiments c2/cl=0. In yet further specific embodiments, the light emitting structure comprises an intermediate non-luminescent body configured downstream of the elongated light transmissive body, and wherein the incoupling position (P) is at the intermediate non- luminescent body. A second concentration of the luminescent material in the intermediate non-luminescent body may essentially be zero wt.%. In embodiments, the term concentration may refer to the concentration of the respective luminescent ions, or the luminescent molecules, or the luminescent quantum dots, etc. When there are more than one type of luminescent species, the concentration refers to the concentrations of a single species. However, in embodiments for each type of luminescent species the herein indicated concentration rules may apply.

Using elements, or parts thereof, that do essentially not have a light absorbing material, especially not the luminescent material, may especially be useful when the second light source light has one or more wavelengths relatively close to one or more wavelengths of the first light source light, such as having a second peak wavelength relatively close to the a first peak wavelength, such as within about +/- 30 nm, like within about +/- 20 nm, or even from the same bin. In such embodiments, the luminescent material may absorb at least part of the second light source light, which may not be desirable. Hence, the optical path of the second light source light through the light emitting structure may be mainly through material that does substantially not absorb the second light source light and/or the optical path (through the light emitting structure) is relatively short.

As indicated above, the invention may further comprise an optical element downstream of the elongated light transmissive body. Such optical element may be configured to extract luminescent material light from the elongated light transmissive body and/or to homogenize the luminescent material light and light source light of one or more of the first light source and the second light source, and/or may be configured to collimate the luminescent material light and light source light of one or more of the first light source and the second light source. Hence, in embodiments the light generating device may further comprise an optical element, such as a beam shaping optical element, wherein the beam shaping optical element comprises a first beam shaping optical element end and a second beam shaping optical element end, wherein the first beam shaping optical element end is optically coupled with the a second body face, and wherein the second beam shaping optical element end and the second structure face coincide. In specific embodiments, the beam shaping optical element comprises a CPC like optical element, such as a CPC (compound parabolic concentrator).

The optical element may comprise a light transmissive material, especially a light transparent (transparent for the luminescent material light), such as alumina, garnet, etc.. Especially, the elongated light transmissive body and the optical element, such as the beam shaping optical element, may have indices of refraction differing at maximum 0.25, such as at maximum 0.22.

Especially, as also indicated above, the light generating device is configured to generate white device light in one or more operational modes. The (white) device light comprises the luminescent material light and the second light source light or the first light source light. Especially, in operational modes it may comprise the luminescent material light and the second light source light and optionally the first light source light.

As there are a plurality of first light sources and/or as there are one or more second light sources, it may be possible to control the spectral power distribution of the device light. By adjusting the contributions of one or more of the first light sources and/or one or more of the one or more second light sources, the spectral power distribution of the device light may be controlled.

The term “controlling” and similar terms especially refer at least to determining the behavior or supervising the running of an element. Hence, herein “controlling” and similar terms may e.g. refer to imposing behavior to the element (determining the behavior or supervising the running of an element), etc., such as e.g. measuring, displaying, actuating, opening, shifting, changing temperature, etc.. Beyond that, the term “controlling” and similar terms may additionally include monitoring. Hence, the term “controlling” and similar terms may include imposing behavior on an element and also imposing behavior on an element and monitoring the element. The controlling of the element can be done with a control system, which may also be indicated as “controller”. The control system and the element may thus at least temporarily, or permanently, functionally be coupled. The element may comprise the control system. In embodiments, the control system and element may not be physically coupled. Control can be done via wired and/or wireless control. The term “control system” may also refer to a plurality of different control systems, which especially are functionally coupled, and of which e.g. one control system may be a master control system and one or more others may be slave control systems. A control system may comprise or may be functionally coupled to a user interface. The control system may also be configured to receive and execute instructions form a remote control. In embodiments, the control system may be controlled via an App on a device, such as a portable device, like a Smartphone or I-phone, a tablet, etc.. The device is thus not necessarily coupled to the light generating device but may be (temporarily) functionally coupled to the light generating device.

Hence, in embodiments the control system may (also) be configured to be controlled by an App on a remote device. In such embodiments the control system of the light generating device may be a slave control system or control in a slave mode. For instance, the light generating device may be identifiable with a code, especially a unique code for the respective light generating device. The control system of the light generating device may be configured to be controlled by an external control system which has access to the light generating device on the basis of knowledge (input by a user interface of with an optical sensor (e.g. QR code reader) of the (unique) code. The light generating device may also comprise means for communicating with other systems or devices, such as on the basis of Bluetooth, WIFI, ZigBee, LiFi, BLE or WiMAX, or another wireless technology.

The system, or apparatus, or device may execute an action in a “mode” or “operation mode” or “mode of operation”. Likewise, in a method an action or stage, or step may be executed in a “mode” or “operation mode” or “mode of operation” or “operational mode”. The term “mode” may also be indicated as “controlling mode”. This does not exclude that the system, or apparatus, or device may also be adapted for providing another controlling mode, or a plurality of other controlling modes. Likewise, this may not exclude that before executing the mode and/or after executing the mode one or more other modes may be executed.

However, in embodiments a control system may be available, that is adapted to provide at least the controlling mode. Would other modes be available, the choice of such modes may especially be executed via a user interface, though other options, like executing a mode in dependence of a sensor signal or a (time) scheme, may also be possible. The operation mode may in embodiments also refer to a system, or apparatus, or device, that can only operate in a single operation mode (i.e. “on”, without further tunability).

Hence, in embodiments, the control system may control in dependence of one or more of an input signal of a user interface, a sensor signal (of a sensor), and a timer. The term “timer” may refer to a clock and/or a predetermined time scheme.

Here below, some specific embodiments are described. 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, the 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. Here, the term “radiation input face” is especially used for the part of the one or more side faces, such as a side face, that is directly irradiated by the light sources. In specific embodiments, also further elucidated below, the radiation exit window has an angle (a) unequal to 0° and unequal to 180° with the radiation input face.

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 essentially one face. This face, here below also indicated as second face (or “second end face” or “second body face”), may comprise a radiation exit window. In embodiments, the second face is the radiation exit window.

Further, the elongated luminescent body comprises one or more side faces.

The number of side faces is herein also indicated with reference N. Hence, in 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. In specific embodiments, N>3. Especially, N=4 (such as especially a rectangular or (rectangular) square cross-section). The elongated luminescent body may have a rectangular cross-section (perpendicular to the axis of elongation). However, other cross-sections, like triangular, or hexagonal, may also be possible. Especially, the elongated luminescent body may comprise four side faces, providing a rectangular cross-section (perpendicular to an axis of elongated of the elongated body). 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°. Hence, in embodiments in specific embodiments the radiation exit window has an angle unequal to 0° and unequal to 180° with one or more of the one or more side faces, especially all of the side faces. Note that the angle a may differ per for different side faces. For instance, a slanted radiation exit window of a bar shaped elongated body may have an angle of al with a first side face, an angle a2=180°-al with a second side face, and angles of 90° with the two other side faces.

The (elongated) luminescent body may thus in embodiments include (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 (H2). 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 (H2) 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. As indicated above, in embodiments the radiation exit window and the radiation input face have an angle (a) unequal to 0° and unequal to 180°.

The light sources are configured in an array. Such array may have a length in the same range as the length of the elongated body. The array may be a ID array or a 2D array. In specific embodiments, the elongated luminescent body and the light source array are configured parallel.

In embodiments, the light sources that are used to generate the luminescent material light may be solid state light sources all of the same bin. In embodiments, the light sources that are used to generate the luminescent material light all have essentially the same peak maximum (peak emission wavelength). In embodiments, the light sources that are used to generate the luminescent material light may essentially all have the spectral power distribution and are all configured to generate essentially the same irradiance at the radiation input face.

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 l _cp1 , wherein the light sources are configured to provide the source light with an intensity maximum l _rc , wherein k _xm -10 nm< l _rc < l _cp1 +10 nm, especially wherein k _xm -5 nm< l _rc < l _cp1 +5 nm, such as wherein k _m -2.5 nm< l _rc < k _m +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).

The converted light can at least partially escape form the radiation exit window, which is especially in optically coupled 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>1.00) 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.

The term “optical contact” and “optically coupled”, similar terms, especially mean that at least part of the light (especially the luminescent material radiation) escaping from one element is at least partly received by another element. Hence, luminescent material light propagating from the radiation concentrator window irradiates optical element.

The term “optical contact” may especially indicate that at least part of the light (especially the luminescent material radiation) escaping from the radiation exit window may enter the optical element with minimal losses (such as Fresnel reflection losses or TIR (total internal reflection) losses)) due to refractive index differences of these elements.

Losses may be minimized by one or more of the following elements: a direct optical contact between the two elements, providing an optical coupling medium (or optically transparent interface material), such as an optical glue or an optical gel, etc., between the two elements, especially the optical coupling medium, such as an optical glue, having a refractive index higher than or equal to the lowest refractive index of the two individual elements and especially lower than or equal to the highest refractive index of the two individual elements, providing the two optical elements in close vicinity (e.g. at a distance much smaller than the wavelength of the radiation), such that the light will tunnel through the material present between the two elements, providing an optically transparent interface material between the two elements. Especially, the optically transparent interface material may have a refractive index higher than the lowest refractive index of the two individual optical elements (here the optical element and the luminescent body). The optically transparent interface material might be a liquid or a gel. In embodiments, the optically transparent interface material may also be a solid material. Further, the optical interface material, such as an optical glue, especially may have a refractive index not higher than the highest refractive index of the two individual elements. Here, the two elements especially refer to the elongated light transmissive body and the optical element, such as a CPC like optical element.

Especially, there may be no optical contact when the distance is at least equal to the wavelength of interest, more especially at least twice the wavelength of interest. In other words, there may be optical contact when the distance is at maximum about the wavelength of interest. For optical contact between the elongated luminescent body and the optical element, the wavelength of interest may e.g. be a peak maximum of the luminescent material light. For optical contact between the elongated luminescent body and the first light source, the wavelength of interest may e.g. be the wavelength of a peak maximum of the luminescent material light or of the first light source light. Hence, in embodiments the distance between the first light source and the elongated luminescent body may be at least equal to or larger than the wavelength of a peak maximum of the luminescent material light, as optical contact may lead to light losses. Hence, the first light sources are optically coupled to the elongated luminescent body but may not be in optical contact therewith.

Alternatively or additionally, an optical anti-reflection coating may be provided on one or both of the surfaces the two individual optical elements.

Instead of the term “optically coupled” also the terms “radiationally coupled” or “radiatively coupled” may be used. The term "radiationally coupled" especially means that a first element and a second element are associated with each other so that at least part of the radiation emitted by the first element is received by the second element.

Likewise, the light sources are radiationally coupled with the luminescent body, though in general the light sources are not in optical contact, such as 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.

Cooling of the elongated body may be relevant. 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. 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.

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 may comprise 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 equal to the 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 lί, such as at least 1.5* lί, like at least 2* lί, such as especially about 5* lί, wherein lί 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 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%.

Hence, the elongated luminescent body is herein also indicated “light transmissive body”, as this body is light transmissive for the luminescent material light. The transmission for the first light source light is (substantially) smaller than for the luminescent material light, as at least part of the first light source light is to be converted into the luminescent material light.

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. The radiation exit window may especially have an angle unequal to 0° and unequal to 180° with the radiation input face, such as angle(s) of 90°. Further, in specific embodiments the radiation exit window has an angle unequal to 0° and unequal to 180° with one or more of the one or more side faces, such as angle(s) of 90°.

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 (H2), with especially L2>W2 and L2>H2. 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 (L2) 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.

In specific embodiments, the length (L2) of the elongated body may be selected from the range of 10-200 mm, such as selected from the range of 40-150 mm.

In a specific embodiment, the light transmissive body has a height (H2) selected from the range of 0.5-100 mm, such as 0.5-10 mm. However, smaller heights may also be possible, such as about 100-500 pm, like at least 140 pm. The light transmissive body is thus especially an integral body, having the herein indicated faces. Especially, the light transmissive body has a height (H2) selected to absorb more than 95% of the light source light. Especially, in embodiments L2>2*H2 and/or L2>2*W2. Especially, L2>5*H2 and/or L2>5*W2. Even more especially, L2>10*H2 and/or L2>10*W2. Yet even more especially, L2>20*H2 and/or L2³20*W2.

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.

Hence, the light transmissive body is especially elongated. Therefore, the length of the light transmissive body is in embodiments larger than the cross-sectional diameter or of the equivalent circular cross-sectional diameter. Here, “cross-sectional” refers to a cross-section perpendicular to the axis or length of elongation of the light transmissive body. The equivalent circular diameter (or ECD) of an (irregularly shaped) two-dimensional shape (such as a cross-section) is the diameter of a circle of equivalent area. For instance, the equivalent circular diameter of a square with side a is 2*a*SQRT(l/t).

The light transmissive body may also be a cylindrically shaped rod. In embodiments the cylindrically shaped rod has one flattened surface along the longitudinal direction of the rod and at which the light sources may be positioned for efficient incoupling of light emitted by the light sources into the light transmissive body. The flattened surface may also be used for placing heatsinks. The cylindrical light transmissive body may also have two flattened surfaces, for example located opposite to each other or positioned perpendicular to each other. In embodiments the flattened surface extends along a part of the longitudinal direction of the cylindrical rod. Especially however, the edges are planar and configured perpendicular to each other.

The side face is especially such flattened surface(s). The flattened surface especially has a relatively low surface roughness, such as an Ra of at maximum 100 nm, such as in the range of 5-100 nm, like up to 50 nm.

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 (see also above).

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 lί (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 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 are especially configured to provide a blue optical power (W _opt ) 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.

As indicated above, the elongated luminescent body may in embodiments comprise a garnet type A3B5O12 luminescent material comprising trivalent cerium.

In yet a further aspect, the invention also provides a projection system or a luminaire comprising the light generating device as defined herein.

The lighting device may be part of or may be applied in e.g. office lighting systems, household application systems, shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, self-lit display systems, pixelated display systems, segmented display systems, warning sign systems, medical lighting application systems, indicator sign systems, decorative lighting systems, portable systems, automotive applications, (outdoor) road lighting systems, urban lighting systems, green house lighting systems, horticulture lighting, digital projection, or LCD backlighting.

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. 1A-1E schematically depict some aspects in relation to the invention;

Fig. 2 schematically depict an alternative solution;

Figs. 3A-3L schematically depict some further aspects in relation to the invention;

Fig. 4 schematically depicts a further embodiments;

Figs. 5A-5B schematically depict some further aspects; and

Fig. 6 shows some simulations.

The schematic drawings are not necessarily to scale. DETAILED DESCRIPTION OF THE EMBODIMENTS

HLD (high lumen density) technology is a new LED-based light-source technology for digital projection. It may make use of a transparent ceramic luminescent rod that can be pumped by arrays of blue LEDs. Most of the light generated inside the rod may be reflected at the rod surface by Total Internal Reflection (TIR) and guided towards the ‘nose’ sides of the rod. At the back side of the luminescent rod a reflector may be placed to send the light back towards the opposite side of the rod where the light may especially be extracted e.g. by a compound parabolic concentrator (CPC). For the rod material, a cerium- doped (lutetium- or yttrium-based) garnet material may especially be used, which can be single-crystalline or poly crystalline. The luminescent rod may have rectangular cross- sectional shape, while concentrators with circular cross sections may provide an even higher extraction efficiency at the exit window. Possible configurations of systems are schematically depicted below (Figs. 1 A-1B). Fig. 1 A schematically depicts a cross sectional view of double-sided HLD module and Fig. IB schematically depicts a cross-sectional view of a single-sided HLD module. Reference 1240 indicates a support for light sources, like a PCB, such as in embodiments a MCPCB (Metal Core Printed Circuit Board). Reference 1010 indicates a light source, such as a solid state light source, like a light diode. Reference 2220 indicates a heat transfer element or heat sink. Refence 100 indicates an elongated light transmissive body comprising a luminescent material 120. Reference 2000 indicates a light emitting structure. Typically, an HLD light source may emit predominantly the converted light from the luminescent conversion material. For all available product this is limited to yellow-green emission.

Fig. 1C schematically depicts a light generating system 1000 comprising a plurality of solid state light sources 1010 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 H2), 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 1011 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) luminescent material 120 configured to wavelength convert at least part of the (blue) light source light 11 into converter light 121, such as at least one or more of green and red converter light 121. As indicated above the luminescent material 120 comprises an A3B50i2:Ce ³⁺ 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 A ₃ B ₅ 0i ₂ :Ce ³⁺ . 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 1010 are configured to provide light source light 1011, which is used as pump radiation. The luminescent material 120 converts the light source light into luminescent material light 121. Light escaping at the light exit window is indicated as converter light 101, and will include luminescent material light 121. Note that due to reabsorption part of the luminescent material light 121 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. Particularly, the angle a is not equal to zero degrees and/or not equal to 180 degrees. In an embodiment, the angle a is 90 degrees.

Hence, Fig. 1C schematically depicts an embodiment of a light generating device 1000 comprising a plurality of first light sources 1010 and a light emitting structure 2000. The plurality of first light sources 1010 are configured to provide first light source light 1011. The light emitting structure 2000 has a structure length LI defined by a first structure face 2141 and a second structure face 2142. The second structure face 2142 comprises a structure radiation exit window 2112. The light emitting structure 2000 comprises an elongated light transmissive body 100. The elongated light transmissive body has a body length L2, defined by a first body face 141 and a second body face 142. Especially, the first body face 141 and the first structure face 2141 coincide. Hence, in embodiments L1>L2. Especially, the elongated light transmissive body 100 further comprises one or more side faces 140, wherein the one or more side faces comprise a radiation input face 111 configured in a light receiving relationship with the plurality of first light sources 1010. As indicated above, the elongated light transmissive body 100 comprises a luminescent material 120 configured to convert at least part of first light source light 1011 into luminescent material light 121. Especially, during operation of the plurality of light sources 1010 at least part of the luminescent material light 121 escapes from the structure radiation exit window 2112.

Figs. 1C-1D schematically depict similar embodiments of the light generating system. Further, 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 1 in Fig. IB further comprise a collimator 1050, such as a CPC.

As shown in Figs. 1C-1D and other Figures, 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.

The collimator 1050 may be supported by an optics interface plate (not shown).

Fig. 1A also schematically depicts an embodiment wherein the radiation exit window 112 has an angle (a) unequal to 0° and unequal to 180° with one or more of the one or more side faces 140. Further, the radiation input face 111 and the radiation exit window 112 may have an angle a unequal to 0° and unequal to 180° with one or more of the one or more side faces 140. Here, angle a is 90°. Reference 15 indicates an array of light sources 1010. In Fig. 1C, and some of the further figures, the n force applying elements are not yet schematically drawn.

Fig. IE 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. IE are not limitative. More shapes are possible; i.e. for instance referred to W02006/054203A, 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 H2, a width W2, and a length L2 extending in mutually perpendicular directions and are in embodiments transparent, or transparent and luminescent. The light is guided generally in the length L2 direction. The height H2 is in embodiments < 10 mm, in other embodiments <5mm, in yet other embodiments < 2 mm. The width W2 is in embodiments < 10 mm, in other embodiments <5 mm, in yet embodiments < 2 mm. The length L2 is in embodiments larger than the width W2 and the height H2, in other embodiments at least 2 times the width W2 or 2 times the height H2, in yet other embodiments at least 3 times the width W2 or 3 times the height H2. 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. IE 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 H2 : width W2 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.

For many applications, a light source is requested or preferred that emits white light, or light with a broader spectrum. This concerns both general lighting applications as well as e.g. light engines for LCD projection systems. In the latter case, this is based on the engines that have been developed for discharge lamps and of which the architecture and components or building blocks are preferred to be re-used. With the current HLD light sources, externally one or more other colors can be mixed dichroically, as is done in e.g. DLP projection systems, as is shown in Fig. 2. However, this requires a large additional volume and additional optical components, and also is applicable only for spectrally well separated beams. The latter means that any spectral overlap of the beams that are to be mixed does result in additional losses. Fig. 2 schematically shows dichroic mixing of different beams to create white light or light with an increased color gamut. The green emission from an HLD engine may in this way be mixed with the collimated light from a large area red and from a large area blue LED (or a red and blue laser) via a dichroic cube or dichroic cross, resulting in a white light beam. Due to the dichroic mixing, there is no spectral overlap of the red, green, and blue fractions that form the white beam.

In contrast, the architectures proposed herein may in embodiments provide a composite spectrum that comprises the converted light as emitted from the luminescent conversion material, as well as laser radiation from one or more laser diodes that is mixed in the optical path of the HLD module, resulting in an output spectrum with reduced saturation, and/or a broader spectral emission, enabling e.g. white light emitting light engines or engines with bi- or multi-modal band emission for increased color gamut light sources. In this way compact high brightness light sources can be realized without the need for external dichroic mixing of separately collimated light of different spectral content and that enable overlapping spectra of the luminescent emission and the laser diode light.

A transparent luminescent concentrator rod may be pumped from one or more sides by e.g. blue LEDs. Amongst others, this invention proposes the injection of blue or red laser light, in specific embodiments p-polarized, e.g. near the rod-CPC interface, in specific embodiments especially at preferably the Brewster angle, such that the injected laser light may reach e.g. in embodiments the rod-CPC interface. Further, especially by suitable matching of the refractive index of the CPC and the concentrator rod, the laser light is substantially transmitted into the CPC, and by that stays within the etendue of the engine (i.e., it is emitted from the CPC within the beam angles as designed for the converted light). This configuration is schematically depicted in Fig. 3A. Fig. 3A schematically depicts a concentrator rod pumped with especially blue LEDs and provided additionally laser diodes. The side-coupled laser diode light enters the rod near the rod-CPC interface, and is substantially transmitted into the CPC within the etendue of the system. Especially, the laser light should not be substantially absorbed by the luminescent material. Therefore, the peak wavelength of the laser radiation should be sufficiently different from the peak absorption wavelength of the luminescent material, or the absorption coefficient of the rod should be sufficiently low. A red laser beam can be injected in this way conveniently, but also a blue laser beam can be injected, provided that the absorption of the blue laser light is sufficiently low to enable a substantial part of it to remain unconverted and be emitted from the engine via the CPC. The laser sources should inject the laser radiation sufficiently close to the rod- CPC interface, otherwise the laser light would undergo multiple (non-TIR) reflections at the long sides of the rod and be attenuated severely.

Hence, Fig. 3A schematically depicts an embodiment wherein the light generating device 1000 further comprises a second light source 1020. Especially, the second light source 1020 is configured to generate second light source light 1021. Further, in embodiments the second light source 1020 comprises a laser light source 20. The second light source 1020, optionally in combination with an optical redirection element 1030, is configured to provide the second light source light 1021 to an incoupling position P between the first structure face 2141 and the second structure face 2142, especially at one or more of the one or more side faces 140 under a first angle b with a normal unequal to 0° such that after incoupling (in the elongated light transmissive body 100) the second light source light 1021 propagates in a direction of the structure radiation exit window 2112. Here, by way of example, two second light sources 1020 are depicted, where a first second light source 1020 provides the second light source light 1021 in a direction of the radiation exit window 112 without an optical element that changes the direction. A second light source 1020 provides the second light source light 1021 in a direction of the radiation exit window 112 with an optical redirection element 1030 that changes the direction. The optical element may be a mirror 1031. Note that possible lenses or other optics downstream of the second light source may also be available, e.g. for collimation or focusing. However, such optics are not herein depicted.

Fig. 3A also shows an embodiment wherein the incoupling position(s) P is (are) at distance from the first structure face 2141 of more than 0.5*L2. In this embodiment, he incoupling position(s) P is (are) close to the radiation exit window 112, such as within 0.25*L2 from the radiation exit window 112.

As indicated above, the second light source light 1021 is p polarized. Further, especially the first angle b is in the range of the Brewster angle ± 5°. The Brewster angle is herein also indicated with br, (see below).

Especially, the elongated light transmissive body 100 has a second dimension D22, perpendicular to the body length L2 and selected from a body height H2 and a body diameter D2, wherein L2>10*D22. Further, especially the incoupling position P is within an incoupling distance Lp of 3*D22 from the second body face 142. In specific embodiments, the incoupling distance Lp is selected from the range of 0.6*D22 - 1.0*D22. Here, in this embodiment D22 is a body height H2 of the elongated light transmissive body 100.

Fig. 3A also schematically depicts an embodiment of the light generating device 1000, further comprising a beam shaping optical element 1050. The beam shaping optical element 1050 comprises a first beam shaping optical element end 1051 and a second beam shaping optical element end 1052. The first beam shaping optical element end 1051 is optically coupled with the second body face 142. The second beam shaping optical element end 1052 and the second structure face 2142 may especially coincide. In specific embodiments, the beam shaping optical element 1050 comprises a CPC like optical element.

Fig. 3A also schematically depicts a control system 300, which may be functionally coupled to the light generating system 1000 or may be comprised thereby. Such control system may also be comprised by or functionally coupled to the light generating system 1000 schematically depicted in other drawings.

The proposed concepts are e.g. applicable for both rectangular and round concentrator rods and CPCs. We show here only a single variant, being e.g. the rectangular configuration.

In a first embodiment, one or more blue (or red) laser diodes with a wavelength substantially higher (or lower) than the peak absorption of the luminescent material is mounted next to the pump-LEDs near the rod-CPC interface. The laser light is injected into the rod at (or close to) the Brewster angle of incidence =atan n (where n is the refractive index of the rod material) (arctangent of n, abbreviated as atan n), while the laser is such oriented that the impinging light is p-polarized (i.e. with the polarization direction in the plane containing the laser beam direction and the normal to the surface of incidence). The laser light may especially be injected sufficiently close to the rod-CPC interface to reach that interface substantially with a maximum of one hit at the reflector behind the opposite side of the rod. This is schematically depicted in amongst others Fig. 3A (and other figures). Hence, the laser light may be incident at the Brewster angle as p-polarized light to prevent Fresnel reflection at the interface. For the LD closest to the rod-CPC interface, the injected laser light may reach the CPC without interaction at the opposite side of the rod. For the second LD, furthest away from the rod-CPC interface, the injected laser light may reach the CPC after having been reflected at the opposite side of the rod, enabling a larger area over which the laser radiation can be injected into the rod. In particular for single-sided irradiated rods this is interesting as a good reflector at the opposite side enables highly efficient reflection of the beam.

In embodiments, the CPC as well as the optical coupling layer between the rod and the CPC may essentially have the same refractive index as the rod. This ensures maximum light extraction from the rod and prevents Fresnel reflection of converted and/or injected laser radiation at the rod-coupler and the coupler-CPC interfaces. In specific embodiment, the CPC is connected directly to the rod, and no additional optical coupling layer is needed. This may be realized by e.g. co-injection molding. In an alternative embodiment, the laser diode emits in another direction, e.g. parallel to the plane of mounting (i.e., parallel to the rod surface), and is redirected by reflective optics (e.g. a reflector or a prism) (see Fig. 3A), such that it arrives at the rod at the Brewster angle and p-polarized. In further alternative embodiments, the laser diode emits perpendicular to the rod surface, and the laser beam is redirected to arrive at the rod surface at the Brewster angle using a redirecting transmissive optical component (e.g. a wedge) in between the LD and the rod (see Fig. 3K).

In an alternative embodiment, the area (part) of the rod near the rod-CPC interface does not comprise the luminescent activator, as can be realized by e.g. poly crystalline composite rods. In this way, the laser diode radiation may show significant overlap with the absorption spectrum of the luminescent material in the concentrator rod, which otherwise would not be feasible as the laser radiation would have been absorbed substantially by the activator. Therefore, this approach enables wider spectral compositions of the (composite) light emitted from the concentrator. This is shown schematically for two different implementation options in Figs. 3B and 3C which schematically depict embodiments wherein LD light is coupled into the rod near the rod-CPC interface and may reach the CPC without substantial absorption in the rod thanks to the composite nature of the rod, comprising a luminescent part and a non-luminescent part, where the latter is located near the rod-CPC interface. In Fig. 3B, implementation of a non-luminescent rod section by absence of the activator material (Ce) in that section is schematically depicted. In Fig. 3C, implementation of a non-luminescent rod section by gluing a non-luminescent light pipe to the luminescent rod, in this example a monolithic optical component comprising both a light pipe section and a CPC section, is schematically depicted.

Other options for the realization of the same principle are then obvious for the person skilled in the art, such as realizing the non-luminescent light pipe and the CPC as discrete components that are connected together by an optical coupler such as a silicone glue or a frit glass layer.

Referring to Figs. 3B-3C the elongated light transmissive body 100 may have an inhomogeneous distribution of the luminescent material 120, wherein a first concentration cl of the luminescent material 120 in the elongated light transmissive body 100 between the first body face 141 and the incoupling position P is higher than a second concentration c2 of the luminescent material 120 in the elongated light transmissive body 100 between the incoupling position P and the second structure face 2142. Especially, in embodiments c2/cl=0 see e.g. Fig. 3B. Alternatively or additionally, in embodiments the light emitting structure 2000 may comprise an intermediate non-luminescent body 1400 configured downstream of the elongated light transmissive body 100, and wherein the incoupling position P is at the intermediate non-luminescent body 1400 (see Fig. 3B).

In alternative embodiments, the LED pump-light and the laser radiation are incident on perpendicularly oriented surfaces of the concentrator rod, which may enable to use some more space for mounting of the laser diodes and/or the optional coupling optics between the laser diodes and the rod, and which may enable a realization of the shortest possible system, as the LED and laser radiation may be injected partly into the same part of the rod. This is schematically indicated in Figs. 3D-3E. Figs. 3D-3E schematically depict luminescent concentrator modules with LD light coupled into the rod near the rod-CPC interface through a side face of the rod that is oriented perpendicular to the side through which the LED pump light is injected into the rod. In Fig. 3D an embodiment of an implementation with maximum cooling of the LEDs and separate sections of the rod for the pump light injection and for the laser radiation injection is schematically depicted. In Fig. 3E an implementation with pump light injection over the full length of the rod, and a rod section where both blue LED pump light and laser radiation is injected is schematically depicted.

So far the examples shown used a single-side injection of pump light. This is a convenient configuration enabling thermal separation of the LEDs and the converter rod and enabling simple system assembly, but with injection light through multiple surfaces the system can be made shorter. Therefore, in alternative embodiments, the LED pump light is injected from two opposite sides. Optionally the laser radiation can be injected through one or two sides, or even more sides. Two configurations using this principle are shown in Fig. 3F-3G. Fig. 3F-3G schematically depicts embodiments of luminescent concentrator modules using dual-sided coupling of light, both for the pump LEDs and for the laser light. In Fig. 3F an embodiment of an implementation with coupling of both pump light and laser light through the same sides of the rod is schematically depicted. In Fig. 3G, an embodiment of an implementation with pump light injection over the full length of the rod, and a rod section where both blue LED pump light and laser radiation is injected is schematically depicted.

As the length of the rod section over which the laser radiation may be coupled into the rod is quite limited, it may make sense, in case of a rectangular rod cross section, to couple the laser radiation into the rod at the side with the shortest width, such that the height H2 is largest. This fits well with the LED coupling efficiency optimization, as in general the side with the largest width is preferred to couple in the LED light to achieve highest coupling efficiency for the LEDs that typically emit light in a beam with a large solid angle subtended. Therefore, in specific embodiments, the laser radiation is coupled into the rod at a different side than where the LED light is injected, as was shown in e.g. Figs. 3D-3E, and where the side for coupling-in the laser radiation has a smaller width than the side for coupling-in the LED pump light.

In an alternative embodiment, an anti-reflex coating is provided on the rod, at least near the rod-CPC interface and at the side where the laser light enters to rod, to maximize the coupling efficiency of the laser light. This enables application of other angles of incidence than the Brewster angle, and enables efficient use of also s-polarized light. For a simple single-layer AR-coating, this coating is optimized for the laser light according to the relation t = l/(4h cos b), where t is the coating thickness, n the refractive index of the coating, l is the laser wavelength and b the angle of incidence.

Multi-layer stacks resulting in efficient suppression of the reflection of the laser radiation at the rod surface may be applied as well. The basic configuration using an AR-coating on the rod for the laser radiation is the same as shown before, but with more freedom in the selection of the angle of incidence for the laser light.

In alternative embodiments, combinations of red and blue LDs are used to couple red and blue laser light into a luminescent concentrator (either into the rod or into the CPC) to enable further extensions of the emission spectra, e.g. for low CCT’s or high color rendering values.

In alternative embodiments, luminescent materials are applied with a somewhat shifted absorption spectrum to enable low absorption of blue laser radiation in the luminescent material. This shift may be either to the shorter wavelength side, e.g. by including Gallium, or to the longer wavelength side, e.g. by including Gadolinium.

Next, we discuss some quantitative considerations for the various embodiments. It can be shown that there are limitations to the choice of the refractive index of the CPC, as total internal reflection at the rod-CPC interface should be prevented. While referring to Fig. 3A, it is noted that m is used for the index of refraction of the elongated light transmissive body 100 and m is used for the index of refraction of the optical element 1050. Further, angles 01 and Q2 are indicated in the drawings. If the CPC index m is too low, total internal refraction (TIR) occurs at the rod-CPC interface. It can be derived that TIR does not occur ifP2 ² >ni ² -sin¾ where m is the refractive index of the rod material and b is the angle of incidence. For b= Q _B =61° and ni=1.84, this implies n ₂ ³1.62. O _B is the Brewster angle.

For a rod height H2, the length L2 over which laser light can be coupled into the rod and that reaches the rod-CPC interface directly (i.e., without any further reflection) is L2=0.54*H2 for light impinging on the rod at the Brewster angle and with m=1.84. For larger angles of incidence this length increases further up to the maximum of Lm _ax = 0.65*H2, but at the cost of quickly increasing Fresnel reflections at the rod surface, which is not preferred. For lower refractive indices of the rod the ratio L/H also increases somewhat; for m=1.5, L2/H2=0.67 for incidence at the Brewster angle, and (L2/H2) _max =0.89. By allowing for a single reflection of the laser radiation at the opposite rod surface, as is e.g. enabled conveniently by the mirror at the opposite side that is indicated in the configuration of Fig. 3 A, therefore, an L2/H2 ratio of 1.1 is found for coupling-in at the Brewster angle and a rod with m=1.84. For Lu(Y)AG rods with a height of 1.6 to 1.9 mm, we therefor find a range of typically 1.7 to 2.2 mm length that can efficiently be used for coupling-in laser radiation. Coupling in laser light at larger distances from the rod-CPC interface is possible but will show a larger loss-penalty and is, therefore, less preferred.

Ray -tracing simulations were used to investigate this further. It was found that for p-polarized light 96.1% of the incident blue flux is transmitted to the CPC exit, for s- polarized light this is 68.9% (and for unpolarized light 82.5%). The angular range of the outcoupled light is between 0° and 30°, well within the intended divergence of > 34°. The angle of incidence should not be much larger than 60°. The CPC in this simulation was designed for an exit divergence of > 34°, but many other targeted beam angles are possible as well.

The directionality of the laser beam and the short travel distances of the laser light in the rod and CPC may result in insufficient homogenization of the different spectral components in the beam exiting the CPC. Therefore, an additional homogenization step may be preferred. Scattering of light is a common way to homogenize spatial and angular light distributions but leads to either additional light losses or increase of etendue.

Homogenization via specular reflection or via (imaging) refractive elements (lenses) may be preferred. The most relevant options are depicted schematically in Figs 3H-3J. The first option is to use an integrating rod, typically comprising flat sides for spatial mixing. This can be realized with a solid light pipe that transports the light based on total internal reflection (TIR), see Fig. 3H, or with a hollow light pipe based on specular reflection at the side walls, see Fig. 31. The main advantage of a hollow light pipe is that, for the same length, the degree of homogenization is higher than for a solid light pipe. However, the reflectors are never ideal, so there are more light losses at these reflections than in the case of a TIR-based integrator. Another approach is to use integrating double lens arrays where the two arrays are positioned at a distance of each other equal to the focal length of the lenses, see Fig. 3J. This has the advantage of not having to be aligned very accurately in lateral directions with the CPC but suffers from Fresnel reflections and non-ideal shapes at the intersection of the lenses. In case of the solid integrator rod, this may a monolithically integrated with the CPC, which would be ideal, or it may be a discrete component that is mounted in optical contact with the CPC via a coupling medium, preferably with a refractive index of both the integrator and the coupling medium close to that of the CPC, or it may be mounted as a discrete component close to the exit of the CPC. In the latter case anti-reflex coatings at entry surfaces and exit surfaces are preferred to minimize losses. Reference 1055 indicates the homogenization elements that ca be used.

Figs. 3K-3L schematically depict two possible embodiments of light incoupling to provide the desired angle. Amongst others, this may be done with a redirection element 1032 or by directly choosing the desired angle. Also a mirror like element may be applied, see Fig. 3 A. In Fig. 3L, reference 1040 indicates an anti -reflection coating. Hence, e.g. Figs. 3A, 3K and 3L schematically depict embodiments wherein the optical redirection element 1030 comprises one or more of a mirror 1031 and a redirection element 1032, wherein the redirection element 1032 may be optically coupled with the elongated light transmissive body 100. In embodiments, the redirection element 1032 may be in optical contact with the elongated light transmissive body 100. In alternative embodiments, the redirection element 1032 may be optically coupled with the elongated light transmissive body 100, but not in optical contact (such as at a distance of at least the wavelength of interest (see also above). Further, Fig. 3L schematically depicts an embodiment wherein the light generating device 1000 further comprises an anti-reflective coating 1040 configured downstream of the second light source 1020 and upstream of the elongated light transmissive body 100.

In alternative embodiments, the laser radiation is coupled into the optical path of the engine directly via the outer surface of the CPC (see Fig. 4). In particular in case of “non-ideal” collimators (or more specifically CPC’s) where e.g. some of the light in the collimator is not kept in TIR, or where e.g. the etendue of the system is somewhat increased, there is opportunity to couple in light through the side wall of the collimator while emitting this light from the emission surface of the collimator within the beam angles of the converted light.

Fig. 5A-5B schematically depict embodiments of a projection system 1 or a luminaire 2 comprising embodiments of the light generating device 1000. Specifically, Fig.

5 A schematically depicts an embodiment of a projection system 1 comprising an embodiment of the light generating device 1000 depicted to generate device light 1001, whereas Fig. 5B schematically depicts an embodiment of a luminaire 2 comprising an embodiment of the light generating device 1000 depicted to generate device light 1001. Reference 301 indicates a user interface, functionally coupled to a control system (not depicted in this drawing). The required blue laser diode optical powers were calculated to achieve color point of the mixed light that are somewhere on the BBL in the CCT range between ca 2000K and 15000K. This is summarized in Table 1. This table indicates the desired optical power ratio of the mixed light to end up with color points on the BBL for various luminescent concentrator compositions resulting in luminescent emission spectra with the indicated dominant wavelength (DWL (nm)). In this table the blue optical laser diode power relative to the luminescent optical power in the beam is given. In addition, the luminous equivalence (LE) of the mixed light, as well as the corresponding chromaticity coordinates (CIE 1931) and the CCT (K) are listed:

Hence, the required blue laser diode optical powers have been calculated to achieve a color point of the mixed light that are somewhere on the BBL in the CCT range between ca 2000K and 15000K. This is summarized in above table 1. To this end, for experimental emission spectra of rods were used as well as two modelled spectra. The third column indicates the dominant wavelength of the luminescent material light escaping from a CPC. The fourth column indicates the ratio between the optical power between the blue laser light that is needed and the luminescent material light in de device light to achieve the desired color point. The fifth column indicates the luminous equivalent of the white device light; columns 6-8 relevant optical properties (color points and color temperature).

If we choose a garnet phosphor composition to realize about 3000K white light, we can e.g. take a YGdAG: Ce rod and add 0.14 W blue (460 nm) laser light per Watt of luminescent light to achieve the BBL at 3050 K. For lower color temperatures, less blue addition is required, for higher color temperatures more addition of blue light is required. At 4000 K (on the BBL), 28 % blue (460 nm) addition is required. So, for 10 klm white light at 3050 K we need 27.7 W optical power, of which (0.14 / 1.14) * 27.7 = 3.4 W blue light. This can be achieved with a single blue laser diode. For 6500 K, for example, which may be suitable for projection systems, we need 0.5 W of blue light per Watt. For a target of more than 16 klm, 30 W green and 15 W blue are required. That can just be achieved with 4 blue laser diodes. Finally, red laser light can also be added, with which the CRI can be tuned and the color point to be chosen can still be tuned reasonably well with a given phosphor. This will be especially interesting for the low color temperatures, where there is a small blue contribution anyway. This can also be achieved with a small number of LDs.

Fig. 6 shows the transmission through an elongated luminescent body when second light source light is coupled into the body at half-length from the first end (and thus also half-length from the second end) as function of the ratio of the length of the elongated luminescent body and the height, i.e. L2/H2. The data are shown for four possible assumptions, with reflectance 95 %, 90 %, 85 % or 80%. As the ratio of the length to the height may be at least 10 and reflectance op 90% may be relatively high, it is clear that the distance from the first end should not be shorter, as loss may then be too high.

Amongst others, the invention proposes a high-lumen-density module containing a luminescent rod architecture with one or more laser diodes emitting light at a wavelength substantially different from the peak absorption wavelength of the luminescent material and mounted at a distance of max 1.5 times the height of the rod, preferably at max 1.1 times the height of the rod (more accurately: related to rod thickness and refractive index difference between rod and CPC) from the rod-CPC interface, injecting p-polarized laser radiation at substantially the Brewster angle of incidence into the rod, where the rod and CPC have a maximum difference in refractive index of 0.25, preferably less than 0.22.

Further, the invention proposes a high-lumen-density module containing a luminescent rod architecture with one or more laser diodes mounted at a distance of max 1.5 times the height of the rod from the rod-CPC interface, injecting p-polarized laser radiation under the Brewster angle of incidence into the rod, where the rod and CPC have a maximum difference in refractive index of 0.22, and where the rod section in which the laser light is injection has a substantially lower activator concentration than in the LED-pumped luminescent part of the rod.

Yet further, the invention proposes a high-lumen-density module containing a luminescent rod architecture with one or more laser diodes mounted at a distance of max 1.5 times the height of the rod from the rod-CPC interface, injecting laser radiation under angles of incidence of more than 45 degrees relative to the surface normal into the rod, where the rod and CPC have a maximum difference in refractive index of 0.22, and where at least the section of the rod where the laser radiation is coupled in is provided with an anti-reflex coating for the laser light.

Yet, the invention also proposes a high-lumen-density module containing a luminescent rod architecture with one or more laser diodes that inject their light near the rod- CPC interface into the CPC.

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.