FIELD OF THE INVENTION

The invention relates to a light generating system and to the use of such light generation system. The invention further relates to a light generating device comprising such light generating system.

BACKGROUND OF THE INVENTION

Speckle reduction or despeckling is known in the art. US2018152680, for instance, describes that laser light reflected off a surface sometimes exhibits a sparkling phenomenon referred to as “speckle.” Laser light is spatially coherent, and when reflected off a diffuse surface, the reflected coherent light waves interfere with each other in a regular pattern that results in a user perceiving speckle. Scanning projectors that utilize lasers for light sources may exhibit speckle across a displayed image. US2018152680 suggests a scanning projection apparatus comprising: one or more scanning mirrors to reflect a light beam in a raster pattern to display an image; a plurality of laser light sources that emit light of substantially the same color to form the light beam, wherein the plurality of laser light sources comprises two laser light sources linearly polarized substantially orthogonal to each other; a polarizing beam splitter positioned to combine light from the two laser light sources to form the light beam; and a controller coupled to receive a commanded light output level and to alternately drive the plurality of laser light sources, the controller configured to drive successive ones of the plurality of light sources to illuminate successive pixels in the image.

SUMMARY OF THE INVENTION

It surprisingly appears that users consider it desirable to perceive light that may have a sparkling effect. For instance, it appeared attractive to use sparkling light in e.g. showrooms or in show cases. However, also for other applications speckle control may be useful. However, many types of light sources cannot provide such effect and/or appear to have a too low power and/or the sparkling effect cannot be adjusted.

Hence, it is an aspect of the invention to provide an alternative light generating system, 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, the invention proposes embodiments including a laser based white light source with adjustable sparkling. The white light source may in specific embodiments comprise a plurality of N lasers giving stimulated emission of a single color. In specific embodiments the coherence length of the light can be (gradually) adjusted and/or otherwise speckle contrast may be controlled. The plurality of N lasers may especially differ in one or more of (i) angle diversity (illumination from different angles), (ii) polarization diversity (use of different polarization states), and/or (iii) wavelength diversity (use of laser sources which differ in wavelength by a small amount). In embodiments, various switching schemes for adjusting the speckle contrast from a relatively low value to a high value with a difference of in specific embodiments at least 30% are herein proposed. For example, a reduction of 55% in speckle contrast can be obtained by using at least N=5 lasers of the same color e.g. blue. The 5 lasers may in embodiments be powered sequentially (i.e. duty cycle = 20%) at 100% power, followed by simultaneously powering the 5 lasers at 20% (i.e. l/N*100%) of the power. In specific embodiments, the plurality of N lasers differs in (i)+(ii) or (i)+(iii) or (ii)+(iii). In yet more specific embodiments, the plurality of N lasers may differ in (i)+(ii)+(iii). In the same way, when RGB lasers may be used then it may even possible that the speckle per color may be controlled. In further specific embodiments the use of a sensor to sense a surface roughness of a surface, such as an illuminated surface, may be sensed. The speckle (contrast) may in embodiments be adapted accordingly. In yet further specific embodiments, elucidated below, even a single laser may be used to provide tunable speckle contrast.

In a first aspect, the invention provides a light generating system comprising (a) one or more light generating devices, (b) optics, and (c) a control system. Especially, a first light generating device of the one or more light generating devices, and the optics, are configured to generate nl first beams of first light, wherein the nl first beams of first light integrated over time spatially overlap. In specific embodiments nl>2, even more especially nl>3. In embodiments, in a first operational mode the control system may be configured to generate a first system beam of first system light comprising integrated over time kl first beams of first light. Especially, the kl beams of first light mutually differ in one or more (i) angular diversity, (ii) polarization, and (iii) centroid wavelength. In yet further specific embodiments, 3<kl<nl. Yet further, in embodiments, in the first operational mode the control system may be configured to maintain a first intensity of the first system light within a predetermined first intensity range while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light. Hence, especially in embodiments the invention provides a light generating system comprising (a) one or more light generating devices, (b) optics, and (c) a control system, wherein a first light generating device of the one or more light generating devices, and the optics, are configured to generate nl first beams of first light, wherein the nl first beams of first light integrated over time spatially overlap, wherein nl>3, wherein in a first operational mode the control system is configured to: (a) generate a first system beam of first system light comprising integrated over time kl first beams of first light, wherein the kl beams of first light mutually differ in one or more (i) angular diversity, (ii) polarization, and (iii) centroid wavelength, wherein 3<kl<nl; and (b) maintain a first intensity of the first system light within a predetermined first intensity range while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light.

With such system it is possible to control speckle. The speckle reduction factor may be controlled, by which a desirable speckle may be introduced. For instance, this may be used in decorative illumination with adjustable sparkling effect and /or varying color point. Hence, in embodiments the light generation system as described herein may be used for decorative illumination with adjustable sparkling. Yet further, adjustable speckle might be used to indicate a safe/unsafe situation. Adjustable speckle may also be used for crowd control, such as to influence in a gentle way people to stay away at certain locations or keep social distance (e.g. a safe distance in relation a virus, like Covid-19). Hence, whereas in general speckle may be reduced, herein, intentionally speckle is at least temporarily allowed, and also tuned.

Speckle is one of the phenomena which can result in sparkling appearance. Speckle may e.g. be observed as a modulation of light intensity when a coherent (or partially coherent) light is incident on a rough surface. The granular appearance of intensity modulation is a result of a random constructive and destructive interference between the light rays reflected from different points of the rough screen. The amount of speckle in the observed image can be quantified by a speckle contrast which is defined as average standard deviation of the intensity distribution (as viewed e.g. by the camera) of the image.

Reduction (or change / modulations) of speckle contrast can be achieved by wavelength diversity, polarization diversity and angle diversity. In general, the speckle contrast reduction factor can be described as l/sqrt(N) where N is the number of incoherent and uncorrelated emitters (of equal intensity) having their light combined at the detector. The table below shows the amount of reduction one can achieve:

As indicated above, the light generating system comprises (a) one or more light generating devices, (b) optics, and (c) a control system.

Hence, the light generating system comprises one or more light generating devices. Each of the one or more light generating devices comprises a light source. In specific embodiments, each of the one or more light generating devices are light sources (respectively).

The term light source may in principle relate to any light source known in the art. It may be a conventional (tungsten) light bulb, a low pressure mercury lamp, a high pressure mercury lamp, a fluorescent lamp, a LED (light emissive diode). Herein, the term “light source” especially relates to a laser light source (see also below).

In embodiments, the light source is a light source that during operation emits at least light at wavelength selected from the range of 380-450 nm. This light may partially be used by the light conversion element (see below). In a specific embodiment, the light source comprises a solid state LED light source (such as a LED or laser diode). The term “light source” may also relate to a plurality of light sources, such as 2-200 (solid state) LED light sources. Hence, 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 light semiconductor light source may be configured on the same substrate. In embodiments, a COB is a multi LED chip configured together as a single lighting module.

The light source has a light escape surface. Referring to conventional light sources such as light bulbs or fluorescent lamps, it may be outer surface of the glass or quartz envelope. For LED’s it may for instance be the LED die, or when a resin is applied to the LED die, the outer surface of the resin. In principle, it may also be the terminal end of a fiber. The term escape surface especially relates to that part of the light source, where the light actually leaves or escapes from the light source. The light source is configured to provide a beam of light. This beam of light (thus) escapes form the light exit surface of the 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 term “laser light source” especially refers to a laser. Such laser may especially be configured to generate laser light source light having one or more wavelengths in the UV, visible, or infrared, especially having a wavelength selected from the spectral wavelength range of 200-2000 nm, such as 300-1500 nm. The term “laser” especially refers to a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation.

Especially, in embodiments the term “laser” may refer to a solid-state laser. In specific embodiments, the terms “laser” or “laser light source”, or similar terms, refer to a laser diode (or diode laser). Hence, in embodiments the light source comprises a laser light source. In embodiments, the terms “laser” or “solid state laser” may refer to one or more of cerium doped lithium strontium (or calcium) aluminum fluoride (Ce:LiSAF, Ce:LiCAF), chromium doped chrysoberyl (alexandrite) laser, chromium ZnSe (Cr:ZnSe) laser, divalent samarium doped calcium fluoride (Sm:CaF2) laser, Er:YAG laser, erbium doped and erbium-ytterbium codoped glass lasers, F-Center laser, holmium YAG (Ho:YAG) laser, Nd:YAG laser, NdCrYAG laser, neodymium doped yttrium calcium oxoborate Nd:YCa4O(BO3)3 or Nd:YCOB, neodymium doped yttrium orthovanadate (NdiYVCU) laser, neodymium glass (Nd:glass) laser, neodymium YLF (Nd:YLF) solid-state laser, promethium 147 doped phosphate glass (147Pm ³⁺ :glass) solid-state laser, ruby laser (AhO3:Cr ³⁺ ), thulium YAG (Tm:YAG) laser, titanium sapphire (Ti:sapphire; AhO3:Ti ³⁺ ) laser, trivalent uranium doped calcium fluoride (U:CaF2) solid-state laser, Ytterbium doped glass laser (rod, plate/chip, and fiber), Ytterbium YAG (Yb:YAG) laser, Yb2O3 (glass or ceramics) laser, etc.

In embodiments, the terms “laser” or “solid state laser” may refer to one or more of a semiconductor laser diode, such as GaN, InGaN, AlGalnP, AlGaAs, InGaAsP, lead salt, vertical cavity surface emitting laser (VCSEL), quantum cascade laser, hybrid silicon laser, etc.

A laser may be combined with an upconverter in order to arrive at shorter (laser) wavelengths. For instance, with some (trivalent) rare earth ions upconversion may be obtained or with non-linear crystals upconversion can be obtained. Alternatively, a laser can be combined with a downconverter, such as a dye laser, to arrive at longer (laser) wavelengths.

As can be derived from the below, the term “laser light source” may also refer to a plurality of (different or identical) laser light sources. In specific embodiments, the term “laser light source” may refer to a plurality N of (identical) laser light sources. In embodiments, N=2, or more. In specific embodiments, N may be at least 5, such as especially at least 8. In this way, a higher brightness may be obtained. In embodiments, laser light sources may be arranged in a laser bank (see also above). The laser bank may in embodiments comprise heat sinking and/or optics e.g. a lens to collimate the laser light.

The laser light source is configured to generate laser light source light (or “laser light”). The light source light may essentially consist of the laser light source light. The light source light may also comprise laser light source light of two or more (different or identical) laser light sources. For instance, the laser light source light of two or more (different or identical) laser light sources may be coupled into a light guide, to provide a single beam of light comprising the laser light source light of the two or more (different or identical) laser light sources. In specific embodiments, the light source light is thus especially collimated light source light. In yet further embodiments, the light source light is especially (collimated) laser light source light. 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 light source is especially configured to generate light source light having an optical axis (O), (a beam shape,) and a spectral power distribution. The light source light may in embodiments comprise one or more bands, having band widths as known for lasers. In specific embodiments, the band(s) may be relatively sharp line(s), such as having full width half maximum (FWHM) in the range of less than 20 nm at RT, such as equal to or less than 10 nm. Hence, the light source light has a spectral power distribution (intensity on an energy scale as function of the wavelength) which may comprise one or more (narrow) bands.

The beams (of light source light) may be focused or collimated beams of (laser) light source light. The term “focused” may especially refer to converging to a small spot. This small spot may be at the discrete converter region, or (slightly) upstream thereof or (slightly) downstream thereof. Especially, focusing and/or collimation may be such that the cross-sectional shape (perpendicular to the optical axis) of the beam at the discrete converter region (at the side face) is essentially not larger than the cross-section shape (perpendicular to the optical axis) of the discrete converter region (where the light source light irradiates the discrete converter region). Focusing may be executed with one or more optics, like (focusing) lenses. Especially, two lenses may be applied to focus the laser light source light. Collimation may be executed with one or more (other) optics, like collimation elements, such as lenses and/or parabolic mirrors. In embodiments, the beam of (laser) light source light may be relatively highly collimated, such as in embodiments <2° (FWHM), more especially <1° (FWHM), most especially <0.5° (FWHM). Hence, <2° (FWHM) may be considered (highly) collimated light source light. Optics may be used to provide (high) collimation (see also above).

Especially, the one or more light generating devices comprise laser light sources. In yet further specific embodiments the one or more light generating devices consist of laser light sources, respectively. Hence, in embodiments the one or more light generating devices may comprise laser diodes. Therefore, in specific embodiments the light generating system may comprise a single laser, or a single laser per color (one or more colors selected from blue, cyan, green, yellow, orange, and red). In other embodiments the light generating device may comprise two or more lasers, especially three or more lasers, for a specific color. In yet other embodiments, light generating device may comprise two or more lasers, especially three or more lasers, such as one or more, especially two or more, even more especially three or more lasers per color (one or more colors selected from blue, cyan, green, yellow, orange, and red), wherein the light generating system thus comprises at least two, such as especially at least three lasers, with in embodiments one or more per single color, especially two or more per single color, such as at least three or more per single color.

Note that the herein described light generating system may in embodiments be configured to generate in an operational mode colored system light. In yet further embodiments, the herein described light generating system may in embodiments only be configured to generate in one or more operational modes colored system light. In yet alternative embodiments, the herein described light generating system may in embodiments be configured to generate in an operational mode white system light. In yet further embodiments, the herein described light generating system may in embodiments only be configured to generate in one or more operational modes white system light. However, in yet further embodiments, the herein described light generating system may in embodiments be configured to generate in one or more operational modes white system light and in one or more other operational modes colored light.

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.

The terms “visible”, “visible light” or “visible emission” and similar terms refer to light having one or more wavelengths in the range of about 380-780 nm. Herein, UV may especially refer to a wavelength selected from the range of 200-380 nm. 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 (at least) visible light. The terms “violet light” or “violet emission” especially relates to light having a wavelength in the range of about 380-440 nm. The terms “blue light” or “blue emission” especially relates to light having a wavelength in the range of about 440-495 nm (including some violet and cyan hues). The terms “green light” or “green emission” especially relate to light having a wavelength in the range of about 495-570 nm. The terms “yellow light” or “yellow emission” especially relate to light having a wavelength in the range of about 570-590 nm. The terms “orange light” or “orange emission” especially relate to light having a wavelength in the range of about 590-620 nm. The terms “red light” or “red emission” especially relate to light having a wavelength in the range of about 620-780 nm. The term “pink light” or “pink emission” refers to light having a blue and a red component. The term “cyan” may refer to one or more wavelengths selected from the range of about 490-520 nm. The term “amber” may refer to one or more wavelengths selected from the range of about 585-605 nm, such as about 590-600 nm.

Specific embodiments are described below, first in relation to a single color. As indicated above, the light generating system comprises optics. The light generating system may comprise polarizers and/or diffusors, especially in relation to controlling the angular diversity and polarization diversity. Such optics are further discussed below. Here, the term “optics” may especially (though not necessarily exclusively) refer to beam combining elements and/or beam splitting elements. The latter may be used to split light source light, such as laser light, in two or more different beams, which may optionally individually be controlled. The former may be used to combine two or more beams into a single beam, such as a beam of system light. The term “optics” may also refer to lenses, holographic elements, optical filters, gratings, beam shaping elements, collimators, etc.. The term “optics” may also refer to polarization rotators, etc.

Beam combining elements may e.g. include one or more of polarization beam combiners, dichroic beam combiners, and fiber optics.

Beam splitting elements may e.g. include one or more of polarization beam splitters, dichroic beam splitters, and fiber optics.

Further, the optics may include (polarization) switches. Hence, by controlling the one or more (laser) light sources of the first light generating device and the (polarization) switches first beams of light may be controlled (see further also below). Note that in embodiments one or more of the nl first beams of first light may also be composed beams. For instance, two or more laser beams may be combined in a single beam. With such embodiments, the intensity of the (composed) beam may be controlled via one or more of pulse-width modulation and (polarization) switches or other switches. Other or additional switches via which the beams may be controlled may be selected from the group consisting of electrical switches, mechanical elements that may block or transmit light (e.g. in certain patterns), PDLC switchable diffusors, a mechanical scanner, a MEMS (Micro- Electro-Mechanical System), etc.

As indicated above, the light generating system comprises one or more light generating devices. Below, a first light generating device is discussed in more detail. The first light generating device may comprise one or more light sources, such as one or more solid state light sources, even more especially one or more laser diodes. Hence, in embodiments the first light generating device may comprise a single laser diode and in other embodiments the first light generating device may comprise a plurality of laser diodes.

Especially, the first light generating device of the one or more light generating devices, and the optics, are configured to generate nl first beams of first light. Note that in embodiments these beams may be generated at the same time, but in yet other embodiments these beams may be generated in different overlapping or non-overlapping time periods. This may also include that one or more of the first beams may not be generated at all during one or more time periods.

Hence, nl first beams may be generated at the same time or in different overlapping or non-overlapping time periods. By controlling these beams (see further below), speckle may be controlled. Therefore, the beams may provide overlapping spots in the near field or in the far field.

For instance, the light generating system may comprise an end window, such as a diffusor, on which the nl first beams provide an overlapping spot. This may be a near- field application.

Alternatively, e.g. in projection applications, the light generating system may be configured to generate an overlapping spot of the nl first beams at some distance of an end window of the light generating system, such as e.g. at a distance selected from the range of 0.5-100 m from such end window, like 1-50 m. This may be a far-field application, wherein the beams of light may be projected on a screen, a wall, or a (3D) object to be illuminated. In both embodiments the nl first beams provide an overlapping spot. Hence, in embodiments over at least part of the path length of the propagating nl first beams.

In embodiments, the overlap may be partial. In yet other embodiments, the overlap may essentially be fully. For instance, a first spot area may be defined by 50-100% of the maximum intensity in the light spot, wherein for each of the light spots of the nl first beams may apply that in the range of at least 10%, such as at least 20% of its spot area overlaps with at least another spot area within the set of the nl first beams. Further, a second spot area may be defined by 5-100% of the maximum intensity in the light spot, wherein for each of the light spots of the nl first beams may apply that they overlap in the range of at least 2%, such as at least 5% of its spot area overlaps with each of the other spot areas within the set of the nl first beams.

The overlap may in embodiments be at the same moment in time. However, as beams may be switched on and off, the overlap may not be at the same time, but only when integrated over time. Hence, the nl first beams of first light integrated over time spatially overlap.

For instance, in embodiments the integration over time may be such that to the human eye it may appear that the intensity and/or spectral power composition of the spot essentially stay the same, while nevertheless over time there are changes visible to the human eye due to one or more (i) angular diversity, (ii) polarization diversity, and (iii) centroid wavelength diversity, which lead to the variable speckle.

As indicated above, the one or more light generating devices, and the optics, are configured to generate nl first beams of first light. Especially, nl>2, more especially nl>3, yet even more especially nl>5. The larger the number of nl, the larger the differences between speckle contrast values can be, and thus the better speckle contrast may be controlled (see also the table above). Hence, especially nl>3.

In a first operational mode the control system may be configured to generate a first system beam of first system light comprising integrated over time kl first beams of first light, wherein the kl beams of first light mutually differ in one or more (i) angular diversity, (ii) polarization, and (iii) centroid wavelength. Below, some embodiments are discussed in more detail wherein angular diversity and/or polarization diversity, and/or centroid wavelength diversity may be obtained. From the possible nl beams, one or more beams may be selected to generate the first system beam of first system light, especially two or more. Hence, in embodiments 2<kl<nl, even more especially 3<kl<nl (as especially nl>3, even more especially nl>5). When there nl beams can be generated, in embodiments for generating the first system beam, integrated over time also nl beams may be used, i.e. in embodiments kl=nl.

In embodiments, the control system may in the first operational mode further be configured to maintain one or more of (a) a first intensity of the first system light within a predetermined first intensity range, and (b) a first color point of the first system light within a predetermined range, while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light.

The phrase “the control system is in the operational mode configured to . . . ”, and similar phrases, especially indicate that the control system is configured to have the light generating system execute the indicated functions, such as “maintain one or more of (a) a first intensity of the first system light within a predetermined first intensity range, and (b) a first color point of the first system light within a predetermined range, while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light” as indicated in the afore-mentioned paragraph. Hence, one might also use the phrase “the light generating system is in the operational mode configured to . . . .”.

The phrase “maintain one or more of (a) a first intensity of the first system light within a predetermined first intensity range, and (b) a first color point of the first system light within a predetermined range, while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light” refers in first embodiments to “maintain a first intensity of the first system light within a predetermined first intensity range, while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light”. Hence, this intensity may be maintained over at least two settings, as during the time that the first intensity is maintained, the relative intensity contributions of the kl first beams of first light to the first intensity of the first system light are varied. Hence, would a first setting be during a first period and a second during a second period, the period included by at least part of the first period (especially the entire first period), a possible intermediate transition period, and at least part of the second period (especially the entire second period), the intensity may be maintained within a predetermined range. Herein, maintaining within a predetermined range may e.g. refer maintaining within +/-20%, such as especially within +/-10% of an average value of the intensity of the first system light. For instance, in embodiments maintaining within a predetermined range may e.g. refer maintaining the spectral power in Watt within +/-20%, such as especially within +/-10% of an average value of the intensity of the first system light. The phrase “maintain one or more of (a) a first intensity of the first system light within a predetermined first intensity range, and (b) a first color point of the first system light within a predetermined range, while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light” refers in second embodiments (alternative or additional to the afore-mentioned first embodiments) to “maintain a first color point of the first system light within a predetermined range, while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light”.

Hence, this first color point may be maintained over at least two settings, as during the time that the first color point is maintained, the relative intensity contributions of the kl first beams of first light to the first intensity of the first system light are varied. Hence, would a first setting be during a first period and a second during a second period, the period included by at least part of the first period (especially the entire first period), a possible intermediate transition period, and at least part of the second period (especially the entire second period), the color point may be maintained within a predetermined range. Herein, maintaining within a predetermined range may e.g. refer maintaining the color point of the first system light essentially constant. Hence, the color point may essentially stay the same.

Colors or color points of a first type of light and a second type of light may be essentially the same when the respective color points of the first type of light and the second type of light differ with at maximum 0.03 for u’ and/or with at maximum 0.03 for v’, even more especially at maximum 0.02 for u’ and/or with at maximum 0.02 for v’. In yet more specific embodiments, the respective color points of first type of light and the second type of light may differ with at maximum 0.01 for u’ and/or with at maximum 0.01 for v’. Here, u’ and v’ are color coordinate of the light in the CIE 1976 UCS (uniform chromaticity scale) diagram.

Especially, in embodiments the control system may in the first operational mode further be configured to maintain a first intensity of the first system light within a predetermined first intensity range while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light.

Hence, a lighting parameter of the first system light may be maintained essentially constant while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light. In this way, speckle reduction values may change over time. In this way, speckle or sparkling appearance may be introduced (which is controllable). As indicated above, the light generating system may thus (further) include a control system.

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 lighting system, but may be (temporarily) functionally coupled to the lighting system.

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 lighting system may be a slave control system or control in a slave mode. For instance, the lighting system may be identifiable with a code, especially a unique code for the respective lighting system. The control system of the lighting system may be configured to be controlled by an external control system which has access to the lighting system 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 lighting system may also comprise means for communicating with other systems or devices, such as on the basis of Bluetooth, WIFI, LiFi, ZigBee, 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 further embodiments are discussed in more detail.

As indicated above, in embodiments the one or more light generating devices, and the optics, are configured to generate nl first beams of first light, wherein the nl first beams of first light integrated over time spatially overlap, wherein nl>2, even more especially nl>3. When there are nl possible first beams, in embodiments two or more of these may have essentially different wavelengths, such as essentially different centroid wavelengths and in other embodiments two or more of these may have centroid wavelengths within a predetermined (relatively narrow) range, such as within about 100 nm, like within about 50 nm, like within about 25 nm.

The term “centroid wavelength”, also indicated as c, is known in the art, and refers to the wavelength value where half of the light energy is at shorter and half the energy is at longer wavelengths; the value is stated in nanometers (nm). It is the wavelength that divides the integral of a spectral power distribution into two equal parts as expressed by the formula kc = X I(k) / (S I(k), where the summation is over the wavelength range of interest, and 1(A) is the spectral energy density (i.e. the integration of the product of the wavelength and the intensity over the emission band normalized to the integrated intensity). The centroid wavelength may e.g. be determined at operation conditions. Would speckle not be controlled via different wavelengths, the centroid wavelengths may thus in embodiments be essentially the same (though this is not necessarily the case (see also above; they may also be different). However, in embodiments wherein speckle may be introduced via different spectral power distributions, two or more of nl first beams of first light may have different centroid wavelengths. Hence, in embodiments at least 2, even more especially at least 3 (when nl>3) of the kl first beams of first light may have mutually different centroid wavelengths within a range of 0.1-100 nm, such as within a range of 0.2-50 nm, such as within about 0.5-20 nm.

In embodiments, the first light generating device in combination with the optics, may be configured to generate at least 3, even more especially at least 4 beams of first light. Hence, in embodiments nl is selected from the range of at least 4, such as at least 5. As indicated above, this may be achieved with a single laser, and using beam splitting elements, beam combining elements, and (polarization) switches. Alternatively or additionally, this may be achieved with a number of light sources, especially nl, such as nl laser light sources.

Hence, in specific embodiments the first light generating device may comprise nl, such as at least 3 laser light sources. In specific embodiments, especially when speckle may be introduced via lasers having different wavelengths, the nl first beams of first light may have mutually different centroid wavelengths within a range of 0.1-100 nm, such as within a range of 0.2-50 nm, such as within about 0.5-20 nm.

Instead of or in addition to differences in centroid wavelengths, angular diversity may be applied to control speckle (differences). Angular diversity may amongst others be obtained by using different diffusors or different arrangements of diffusors. This is indicated with different diffusor configurations. Hence, in embodiments the light generation system may comprise kl different diffusor configurations for each of the kl beams. For instance, different beams may intercept different diffusors or different parts of the same diffusor. The beams downstream of the different diffusors or different parts of the diffusor(s) may have different spatial power distributions. Hence, cross-sectional power distribution of the beams will be different downstream of the kl different diffusor configurations. Therefore, in embodiments the kl different diffusor configurations may have kl different orientations of polarization planes.

Especially, in order to modify speckle contrast, different interacting beams/components may in embodiments be independent and un-correlated. This can in embodiments be done with a fast moving diffuser (or other elements to obtain angular diversity) or with stationary diffusers (or other elements to obtain angular diversity) and fast beam switching (and combining). Combinations may also be possible.

In embodiments, the one or more diffusors may be selected from surface diffusors and volume diffusors. Also combinations of different types of diffusors may be applied. In embodiments, volume diffusors may be applied. They may have even more impact on the spatial coherence than surface diffusors.

In embodiments, diffractive diffusors may be applied.

In embodiments, different diffusers may have different spatial and phase patterns. Yet further, in embodiments different areas of a diffuser may have different phase patterns. Especially different phase patterns are desirable, as with such embodiments speckle may be controlled. Spatial patterns may vary or may not vary; phase patterns especially vary to reduce speckle.

In specific embodiments, angular diversity may be obtained using a digital micromirror device (DMD). Hence, such DMD may be used as diffusor and/or such DMD may be used to generate a number of first beams. Hence, the light generating device may comprise one or more DMDs. Especially, in embodiments the tilt of the mirrors may be controlled randomly.

Alternatively or additionally, angular diversity may (also) be obtained using mirrors and/or lenses to change angular distribution.

Alternatively or additionally, angular diversity may amongst others (also) be obtained by using retarders or other phase shift elements (see also below).

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), wherein relative to a first position within a beam of light from the light generating means, a second position in the beam of light closer to the light generating means is “upstream”, and a third position within the beam of light further away from the light generating means is “downstream”.

In embodiments, diffusors may be controllable. Diffusors may be controllable when the extend of diffusion may be controlled. Diffusors, however, may also be controllable when they may intercept at least part of a beam or when they may not intercept at least part of the beam, or when the part of the beam that is intercepted may be controllable. Hence, in embodiments the kl different diffusor configurations may be obtained integrated over time, and there may be less than kl light source used for creating kl different spatial power distributions. Instead of or in addition to differences in centroid wavelengths, polarization diversity may be applied to control speckle (differences). Different polarizations may amongst others be obtained by using different polarizers and or different arrangements of polarizers or different polarization arrangements. Therefore, with polarization diversity, different polarization directions may be provided.

Hence, in embodiments the light generation system may comprise kl different polarizer configurations for each of the kl beams. For instance, different beams may intercept different polarizers or different parts of a polarizer having a spatial distribution of (different) polarizations. The beams downstream of the different polarizers or different parts of the polarizer(s) may have different spatial power distributions. Hence, cross-sectional power distribution of the beams will be different downstream of the kl different polarizer configurations.

In embodiments, polarizers may be controllable. Polarizers may be controllable when the polarization may be controlled. Polarizers, however, may also be controllable when they may intercept at least part of a beam or when they may not intercept at least part of the beam, or when the part of the beam that is intercepted may be controllable. Hence, in embodiments the kl different polarizer configurations may be obtained integrated over time, and there may be less than kl light source used for creating kl different spatial power distributions.

Therefore, in embodiments the kl beams of first light may comprise kl different polarizations or kl different polarization distributions.

Basically there may be s and/or p polarizations. Light after interaction with a rough surface may also become partially polarized, and the beams can have different degrees of polarization. One may thus also apply spatially modulating polarization of a beam (with (larger) cross-section) by spatially rotating polarization in different parts of the beam (e.g. with LCOS modulator).

Especially, in order to modify speckle contrast, different interacting beams/components may in embodiments be independent and un-correlated. This can in embodiments be done with a fast moving polarizers or with stationary polarizers and fast beam switching (and combining). Combinations may also be possible.

In embodiments, polarizers may be controllable. Polarizers may be controllable when the extend of diffusion may be controlled. Polarizers, however, may also be controllable when they may intercept at least part of a beam or when they may not intercept at least part of the beam, or when the part of the beam that is intercepted may be controllable. Hence, in embodiments the kl different polarizer configurations may be obtained integrated over time, and there may be less than kl light source used for creating kl different spatial power distributions.

Hence, with the invention, in embodiments with a single laser, or with a plurality of lasers, it is possible to generate over time nl first beams of first light, which may in the near filed or far field over time be overlapping spots. Especially, nl>3. In the first operational mode the control system is configured to: (a) generate a first system beam of first system light comprising integrated over time kl first beams of first light, wherein the kl beams of first light mutually differ in one or more (i) angular diversity, (ii) polarization, and (iii) centroid wavelength, wherein 3<kl<nl. Further, the system may be configured to (b) maintain a first intensity of the first system light within a predetermined first intensity range while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light. As indicated above, the nl first beams of first light integrated over time spatially overlap. In this way, a plurality of different wavelengths and/or spatial polarizations and/or angular diversity may be created, thereby allowing control of speckle, as (over time) individual beams may be controlled.

A first system beam of first system light may be provided which over time may comprise different contributions of kl different first beams of first light. They may over at least part of their path length overlap with each other, when integrated over time, such as on a screen, wall, etc., or on an exit window. The kl beams of first light mutually differ in one or more (i) angular diversity, (ii) polarization, and (iii) centroid wavelength. Hence, the kl first beams of first light integrated over time spatially overlap (in the far field or near field). Though a first system beam of first system light may be provided which over time may comprise different contributions of kl different first beams of first light, the intensity may in the operational mode essentially stay constant. Hence, a first intensity of the first system light within a predetermined first intensity range may be maintained while varying over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light.

To be able to observe differences in speckle, the changes may especially be relatively large. Differences in speckle contrast values may e.g. be at least 20 percent points, such as at least 30 percent points (see further also below). Further, to be able to observe differences in speckle, the period of time of the different speckle values, may not be too short or too long, such as e.g. selected from the range of 0.1-300 seconds, like 0.1-180 seconds, such as in embodiments 0.1-120 seconds, like e.g. at least 0.5 seconds, such as at least 1 second, like at least about 2 seconds. The change between two speckle contrast values have a relatively large difference may also not take too long, and may take in embodiments at maximum 300 second, such as at maximum 180 seconds, like at maximum 120 seconds, such as at maximum 60 seconds. The change may thus in embodiments be gradual, like stepwise with multiple steps, or essentially stepless, or may essentially be instantaneous.

Especially, in embodiments the integrated time period of the two periods with (substantially) different speckle contrast values including the intermediate change period may not last longer than 300 second, such as at maximum 180 seconds, like at maximum 120 seconds, and may last at least about 2 second, such as at least about 5 seconds, though shorter intermediate change periods are not excluded, such as e.g. at least about 0.1 seconds.

Hence, in specific embodiments in the first operational mode the control system may be configured to vary the relative intensity contributions of one or more of the kl first beams of first light sequentially of time periods that last between 0.1-300 seconds, like 0.1-180 seconds, such as in embodiments 0.1-120 seconds, like e.g. at least 0.5 seconds, such as at least 1 second, like at least about 2 seconds.

Note that the phrase “sequentially of time periods that last between x-y seconds”, and similar phrases, may also refer the sequential periods wherein the lengths of the sequential periods is selected from the range of x-y second, but the length of the periods may (randomly) vary in time.

Hence, time periods with high and low speckle contrast may in embodiments alternate.

The selection of the periods, but also the selection of the beams that are used, whether or not with a reduce amount, may be done in a regular way or in a non-regular way. the no-regular way may e.g. be random or pseudo-random. Control of intensity of the beams may be done via controlling the light sources, such as via pulse-width modulation. Hence, by controlling the duty cycle, the relative intensity contribution may be controlled. Additionally or alternatively, control of intensity of the beams may be done with e.g. (polarization switches, etc.). Hence, in embodiments in the first operational mode the control system may especially be configured to vary one or more of (i) the relative intensity contributions, and (ii) the time periods (as defined herein) to a regular scheme or a random scheme. Combinations of regular and random may also be included, such as a regular scheme of sets of random varied intensities and/or time periods, or an irregular scheme of sets of regular varied intensities and/or periods, or an irregular variation of the time with a regular variation of the intensities, or a random variation of the intensities in regular time periods, etc. As indicated above, time periods may in embodiments selected from the range of 0.1-300 seconds, like 0.1-180 seconds, such as in embodiments 0.1-120 seconds, like e.g. at least 0.5 seconds, such as at least 1 second, like at least about 2 seconds. Would time periods be varied in a (more) regular way, then frequencies may be used which especially be visible to the human eye. Hence, in embodiments in the first operational mode the control system is configured to vary the relative intensity contributions of one or more of the kl first beams of first light over time with a frequency selected from the range of 60 Hz - to 0.003 Hz, 60-0.06 Hz, like in embodiments about 60-0.08 Hz, like e.g. at maximum 2 Hz, such as at maximum 1 Hz, like at maximum about 0.5 Hz.

Duty times may in embodiments vary from 0-0.95, such as from 0.05-0.95. Different beams may be generated with different duty cycles. Further, even when having the same duty cycle, the position of the one-period within the period may in embodiments differ for different beams (but may also be the same in other embodiments).

An easy way to introduce relative large differences in speckle contrast values may be obtained by selecting a time period of a set of one or more light sources, such as lasers, especially a relatively small number of light sources, at relatively high power, and selecting another time period a set of one or more light sources, such as lasers, especially a relatively larger number of light sources, at relatively smaller power. The sets may even be the same, wherein in one time period one or more of the lasers are at relatively higher power, and wherein in another time period, all lasers are at relatively small or moderate power.

Hence, in specific embodiments in the first operational mode the control system may be configured to vary the relative intensity contributions of the kl first beams of first light over time according to a schedule wherein in a first time period the first intensity of the first system light is for at least 70% defined by a first set of first beams of first light and wherein in a second time period the first intensity of the first system light is for at least 70% defined by second set of first beams of first light. Hence, in the first time period at least 70% of the intensity of the first system light may be defined by the first set, and in the second time period 70% of the intensity of the first system light may be defined by the second set. These percentage may also be higher, like at least 80%, such as at least 90%, or even 100% (see also the examples below). In specific embodiments, the different sets may comprise one or more different first beams of first light. However, in other embodiments the different sets may comprise essentially the same first beams of first light. As indicated above, in specific embodiments the first time period and second time period may last for a time period selected from the range of 0.1-120 seconds. A series of first and second time periods, optionally separated by transition periods, may be executed.

In specific embodiments, the first set of first beams or the second set of first beams may consist of a single beam of first light.

As indicated above, differences in speckle contrast values may e.g. be at least 20 percent points, such as at least 30 percent points. Especially, in embodiments in the first operational mode the control system may be configured to vary over time relative intensity contributions of the kl first beams of first light to the first intensity of the first system light such that speckle reduction factors differ in time with at least 20 percent points, more especially at least 30 percent points, like in yet more specific embodiments at least 35 percent points.

In embodiments, the speckle contract level may be switched from a low speckle contrast level (directly) to a high speckle contrast level, and/or vice versa.

In embodiments, the speckle contract level may be switched from a low speckle contrast level (directly) via medium contrast level to (directly) a high speckle contrast level, and/or vice versa.

In embodiments, the speckle contract level may be switched from a low speckle contrast level (directly) via a high speckle contrast level to (directly) a low speckle contrast level, and/or vice versa.

In embodiments, a low speckle contrast level may be <45%, and more especially <40%, and most especially <35%. In embodiments, a high speckle contrast level may be >70%, and more especially >80%, and most especially >90%. In embodiments, the medium speckle contrast level may be in the range from 45% to 70%.

In embodiments, the speckle reduction may be a specific time interval may be at least 50%.

In embodiments, the speckle reduction may be varied as function of time wherein the speckle reduction covers at least a value in at least 3 different ranges from the group of 0-20%, 20-40%, 40-60%, and 60-80%.

Embodiments may be repeated in a regular or random pattern. Especially, parameters like time periods, intensities, speckle contrast differences, etc. may be controlled in a random way.

As indicated above, in embodiments a single laser, and using beam splitting elements, beam combining elements, and (polarization) switches, may be applied to obtain the nl first beams. Alternatively or additionally, this may be achieved with a number of light sources, especially nl, such as nl laser light sources.

Hence, in embodiments the first light generating device may comprise a single first light source configured to generate first light source light, wherein the optics are configured to generate the nl first beams of first light, wherein the optics comprise beam splitting elements, wherein the light generation system further comprises (e.g. nl, or more) switches configured to control the nl first beams, wherein the control system is configured to control the switches (and the beam splitting element), and wherein the first light source comprises a laser. Especially, the switches may be controllable (by the control system).

Alternatively (or additionally), the first light generating device comprises nl light sources configured to generate light source light , wherein the nl light sources and the optics are configured to generate the nl first beams of first light, wherein the control system is configured to control the nl light sources, and wherein the nl light sources comprise lasers.

Above described embodiments amongst others include embodiments wherein the nl first beam of first light may all have centroid wavelength is a limited range, such as within 100 nm, though other embodiments are described above too. Here below, some embodiments are further elucidated especially in relation to using different colors.

If one would combine just three lasers R+G+B without any further measures one may observe speckle in resulting (white) light. The perception of speckle may be different for different spectral ranges. If one would like to adjust the amount of sparkle / speckle in this white beam, it may be useful to introduce another degree of freedom to at least one of the color channels, based either on polarization, angular or wavelength diversity. Would one desire to modulate the amount of speckle from e.g. the green channel contribution (most visible to the eye), another (independent) (4 ^th ) green source may be provided, and/or a polarization switch may be provided in the green channel, and/or e.g. a movable diffuser in the green channel may be provided, or realize angular diversity by other means. In embodiments, angular diversity may also be controlled by using switching beams through different fiber optical paths, or reflecting the beam from a deformable mirror, etc. In embodiments, speckle may be controlled using electrically switchable optics, e.g. liquid crystal optics.

Hence, in embodiments different types of first light may be introduced. In specific embodiments, wherein the first light of one or more first beams of first light have a first type of color, wherein the first light of one or more other first beams of first light have a second type of color, and wherein the first light of at least two yet other first beams of first light have a third type of color, and the first light of at least two yet other first beams of first light may have centroid wavelengths within a range of 0-100 nm, such as 0-50 nm, and wherein in the first operational mode the control system is configured to generate the first system beam of white first system light. Hence, the first light of at least two yet other first beams of first light have mutual centroid wavelength differences within a range of 0-100 nm, such as especially within a range of 0-50 nm.

The first light of at least two yet other first beams of first light may be the result of providing the first light with different centroid wavelengths. Alternatively or additionally, speckle may be introduced by providing angular diversity and/or polarization diversity to one or more first beams of first light , leading to at least two first beams of first light (when integrated over time) which may differ in one or more of angular diversity and (spatial distribution of the) polarization.

In yet other embodiments, the above described system may include a second light generation device, which may essentially be the same as the first light generation device. However, in such embodiments the light generated by the first light generating device and the second light generating device may differ in color point, such as having different colors (see above).

Hence, in embodiments the light generation system may further comprise a second light generation device, wherein: (a) the second light generating device and the optics are configured to generate n2 second beams of second light; (b) the n2 second beams of second light spatially overlap, wherein n2>l, especially n2>2, even more especially n2>3, such as in embodiments n2>4, like in yet further specific embodiments n2>5; (c) the nl first beams of first light and the n2 second beams of second light spatially overlap; and (d) the first light of the nl first beams define a first color gamut, wherein the second light of the n2 first beams define a second color gamut, wherein the first color gamut and the second color gamut do not overlap. In specific other embodiments, however, the first color gamut and the second color gamut may partially overlap.

In yet other embodiments, the above described system may include a second light generation device and a third light generation device, which may essentially be the same as the first light generation device. However, in such embodiments the light generated by the first light generating device and the second light generating device and the third light generation device may differ in color point, such as having different colors (see above). Of course, more than three different light generation devices may be comprised by the light generating system.

Hence, in yet a further embodiment the light generation system may yet further comprise a third light generation device, wherein: (a) the third light generating device and the optics are configured to generate n3 third beams of third light; (b) the n3 third beams of third light spatially overlap, wherein n3>l, especially n3>2, even more especially n3>3, such as in embodiments n3>4, like in yet further specific embodiments n3>5; (c); the nl first beams of first light, and the n2 second beams of second light, and the n3 third beams of third light spatially overlap; and (d) wherein the third light of the n3 first beams define a third color gamut, wherein the first color gamut, the second color gamut, and the third color gamut do not overlap. In specific other embodiments, however, the first color gamut and the second color gamut and the third color gamut may partially overlap.

Especially, the one or more light generating devices comprise lasers. Even more especially, all of the light generating devices comprise one or more lasers (wherein the lasers of the different light generating device may provide mutually differing colors).

In yet a further aspect, the invention also provides a lamp or a luminaire comprising the light generating system as defined herein. The luminaire may further comprise a housing, optical elements, louvres, etc. etc... The lamp or luminaire may further comprise a housing enclosing the light generating system. The lamp or luminaire may comprise a light window in the housing or a housing opening, through which the system light may escape from the housing. In yet a further aspect, the invention also provides a projection device comprising the light generating system as defined herein. Especially, a projection device or “projector” or “image projector” may be an optical device that projects an image (or moving images) onto a surface, such as e.g. a projection screen. The projection device may include one or more light generating systems such as described 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. The lighting device (or luminaire) may be part of or may be applied in e.g. optical communication systems or disinfection systems.

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:

Fig. 1 schematically depicts an embodiments;

Figs. 2-4 schematically depict some lighting schemes;

Figs. 5 schematically depicts a further embodiment;

Fig. 6 schematically depicts an embodiment of a configuration to electronically generate 4 independent modes;

Fig. 7 schematically depicts an embodiment of a very compact configuration to electronically generate 2 independent polarization modes;

Figs. 8a-8c schematically depict some aspects; and

Fig. 9 schematically depict some applications.

The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In embodiments, amongst others a laser based white light source with adjustable sparkling is proposed. In embodiments, the white light source may comprise a plurality of N lasers giving stimulated emission of a single color where the coherence length of the light can be (gradually) adjusted and/or otherwise speckle contrast may be controlled. The plurality of N lasers may differ in (i) angle diversity (illumination from different angles), (ii) polarization diversity (use of different polarization states), and/or (iii) wavelength diversity (use of laser sources which differ in wavelength by a small amount), see Fig.1. Fig. 1 is further explained below.

In further specific embodiments the use of a sensor to sense a surface roughness of a surface, such as an illuminated surface, may be sensed; the speckle (contrast) may in embodiments be adapted accordingly, see also Fig. 1 (see further below).

Other embodiments may also be possible, see also below.

Amongst others, various switching schemes are proposed below for adjusting the speckle contrast from a relatively low value to a high value with a difference of at least 30%. For example, a reduction of 55% in speckle contrast can be obtained by using at least N=5 lasers of the same color e.g. blue. The 5 lasers are powered sequentially (i.e. duty cycle = 20%) at 100% power, followed by simultaneously powering the 5 lasers at 20% (i.e. l/N*100%) of the power, see e.g. Fig. 2. Fig. 2 is further explained below.

Other embodiments of the laser driving scheme include changing the order in which the lasers are pulsed (Fig. 3), changing the amplitude and pulse time (Fig. 4) or a combination of these two methods may also be applied. Figs. 3-4 is further explained below.

Other embodiments, however, may also be possible.

In the same way when RGB lasers may be used then it may even possible that the speckle per color may be controlled, see e.g. Fig. 5. Fig. 5 is further explained below.

Angular diversity may be realized by sending the laser beam through a weak diffuser. This creates an independent mode. By moving the diffuser sufficiently fast, N independent modes are generated that lower the speckle contrast to a value proportional to 1/ N. Since a moving diffuser might introduce mechanical vulnerability, there is a need for a contraption that electronically generates independent speckle modes, without moving mechanical components.

As indicated above, Fig. 1 schematically depicts an embodiment of a light generating system 100. The system 100 comprises (a) one or more light generating devices 1000, (b) optics 200, and (c) a control system 300. Here, by way of example, the system 100 comprises three light generating devices, indicated with references 1100, 1200, and 1300.

Light generating devices 1200 and 1300 are optional, and may e.g. be laser systems without the ability to control speckle as such, though other options may also be possible (see below). The first light generating device 1100 may be used to control speckle.

The first light generating device 1100 of the one or more light generating devices 1000, and the optics 200, in this embodiment, is configured to generate nl first beams 1110 of first light 1111. The nl first beams 1110 of first light 1111 integrated over time spatially overlap. Especially, nl>3, even more especially at least 4. Here, nl=5.

To this end, the first light generating device 1100 comprises nl light sources 10, especially laser light sources. The laser light sources are indicated with references nl 1- nl5.

In a first operational mode, the control system 300 is configured to generate a first system beam 110 of first system light 111 comprising integrated over time kl first beams 1110 of first light 1111. Especially, the kl beams 1110 of first light 1111 mutually differ in one or more (i) angular diversity, (ii) polarization (diversity), and (iii) centroid wavelength. Especially, 3<kl<nl. As depicted in Fig. 1, kl=nl=5.

In the first operational mode the control system 300 is configured to maintain a first intensity of the first system light 111 within a predetermined first intensity range while varying over time relative intensity contributions of the kl first beams 1110 of first light 1111 to the first intensity of the first system light 111.

Fig. 1 may e.g. depict an embodiment wherein all beams 1110 are generated by laser light source, though other light sources may in embodiments also be possible. Here, five laser light sources for the first light generating system 1100 are depicted.

Referring also to Fig. 8a, at least 3 of the kl first beams 1110 of first light 1111 have mutually different centroid wavelengths within a range of 0.1-100 nm, and wherein the one or more light generating devices 1000 comprise lasers.

The possible angular diversity is indicated with references al-a5. For instance, angular diversity may be obtained with diffusors. Different diffusors and/or different diffusor configurations may lead to different angular diversities for the beams. Hence, in embodiments there may be kl different diffusor configurations 140 for each of the kl beams 1110 (see also Fig. 8c). Different diffusors and/or different diffusor configurations are both indicated as diffusor configurations 140.

Polarization differences may be obtained with different polarizers and/or different polarization configurations. Different polarizers and/or different polarization configurations are both indicated as polarization configurations 150, see also Fig. 8c. Hence, in embodiments the kl beams 1110 of first light 1111 comprise kl different polarizations or kl different polarization distributions. The possible polarization diversity is indicated with references pl-p5.

Reference 105 indicates a radiation exit window, which may also be indicated as “exit” or “end window”.

Also referring to Figs. 2-4 in the first operational mode the control system 300 is configured to vary the relative intensity contributions of one or more of the kl first beams 1110 of first light 1111 sequentially of time periods that last between 0.1-120 seconds. For instance, in the first operational mode the control system 300 may be configured to vary one or more of the relative intensity contributions, and the time periods according to claim 5 according to a regular scheme or a random scheme. For instance, in the first operational mode the control system 300 is configured to vary the relative intensity contributions of one or more of the kl first beams 1110 of first light 1111 over time with a frequency selected from the range of 60 Hz - to 0.003 Hz. Especially, in embodiments in the first operational mode the control system 300 is configured to vary the relative intensity contributions of the kl first beams 1110 of first light 1111 over time according to a schedule wherein in a first time period the first intensity of the first system light I l l is for at least 70% defined by a first set of first beams 1110 of first light 1111 and wherein in a second time period the first intensity of the first system light I l l is for at least 70% defined by second set of first beams 1110 of first light 1111. For instance, the first time period and second time period last for a time period selected from the range of 0.1-120 seconds. As schematically depicted, in embodiments the first set of first beams or the second set of first beams may consist of a single beam of first light. The first beams 1111 of first light 1111 are indicated with 1111a, 1111b, 1111c, 111 Id, and 111 le, respectively.

Fig. 1 also schematically depicts an embodiment wherein the first light generating device 1100 comprises nl light sources 10,20,30,40,50 configured to generate light source light 11,21,31,41,51, wherein the nl light sources 10,20,30,40,50 and the optics 200 are configured to generate the nl first beams 1110 of first light 1111, wherein the control system 300 is configured to control the nl light sources 10,20,30,40,50, and wherein the nl light sources 10,20,30,40,50 comprise lasers.

Especially, in the first operational mode the control system 300 is configured to vary over time relative intensity contributions of the kl first beams 1110 of first light 1111 to the first intensity of the first system light 111 such that speckle reduction factors differ in time with at least 30 percent points.

Reference 310 indicates a sensor. This may especially be an optical sensor. The sensor may be configured to one or more of estimate roughness of a surface and determine speckle at a surface. In this way, the sensor signal may be used to control the light generating system.

Figs. 2-4 schematically depict possible pump schemes assuming 5 different beams, such as provided with 5 different lasers. Fig. 2 shows an embodiment of pulse driving using multiple laser, in a regular sequence. Fig. 3 shows an embodiment of pulse driving using multiple lasers, wherein a sequence is change, each with same time and amplitude. Fig. 4 shows an embodiment of pulse driving using multiple lasers, with a regular sequence but with pulse amplitude and pulse length variations. In Fig. 2, tc refers to the intermediate change period, which are here chosen much shorter than the other time periods. However, this is not necessarily the case. Referring to Fig. 5, an embodiment is schematically depicted of the light generation system 100, further comprising a second light generation device 1200. The second light generating device 1200 and the optics 200 are configured to generate n2 second beams 1210 of second light 1211. The n2 second beams 1210 of second light 1211 spatially overlap. For instance, n2>3. The nl first beams 1110 of first light 1111 and the n2 second beams 1210 of second light 1211 spatially overlap. Especially, the first light 1111 of the nl first beams 1110 define a first color gamut, wherein the second light 1211 of the n2 first beams 1110 define a second color gamut, wherein the first color gamut and the second color gamut do not overlap.

Further, the light generation system 100 may also comprise a third light generation device 1300. The third light generating device 1300 and the optics 200 are configured to generate n3 third beams 1310 of third light 1311. The n3 third beams 1310 of third light 1311 spatially overlap. For instance, n3>3. Especially, the nl first beams 1110 of first light 1111, and the n2 second beams 1210 of second light 1211, and the n3 third beams 110 of third light 1311 spatially overlap. Especially, the third light 1311 of the n3 first beams 1110 define a third color gamut, wherein the first color gamut, the second color gamut, and the third color gamut do not overlap.

The second light generating device 1200 comprises n2 light sources 10, especially laser light sources. The laser light sources are indicated with references n21-n25.

The third light generating device 1200 comprises n3 light sources 10, especially laser light sources. The laser light sources are indicated with references n31-n35.

A proposal for a device that electronically generates four independent modes is shown in Fig. 6. Light from a laser is sent through a polarization switch 1 where the polarization state of the beam can be switched from p to s. A first polarizing beam splitter passes light in the p-state and reflects light in the s-state. When switch 1 generates a p-state, light passes the first polarizing beam splitter and goes through a diffuser A, reflects from a mirror, passes a polarizing beam combiner, passes switch 4, passes another polarizing beam combiner, passes switch 5 that converts it into s-state, and finally reflects from the last polarizing beam combiner to the light exit. Analogously, when polarization switch 1 generates an s-state, light can be directed through diffuser B, C or D with suitable settings of polarization switches 2, 3, 4 and 5, and can be passed through to the light exit.

Here, references M, BC, PS, and BS indicate a mirror, a beam combiner, a polarization switch, and a beam splitter, respectively. References D indicate diffusors. Hence, Fig. 6 schematically depicts an embodiment of the light generation system 100, wherein the first light generating device 1100 comprises a single first light source 10 configured to generate first light source light 11, wherein the optics 200 are configured to generate the nl first beams 1110 of first light 1111, wherein the optics 200 comprise beam splitting elements BS, wherein the light generation system 100 further comprises nl switches PS configured to control the nl first beams 1110, wherein the control system 300 is configured to control the switches PS and the beam splitting element BS, and wherein the first light source 10 comprises a laser. Reference 10 indicates a laser light source.

As indicated above, Fig. 6 is a specific embodiment of the light generating system 100 comprising (a) one or more light generating devices 1000, (b) optics 200, and (c) a control system, wherein a first light generating device 1100 of the one or more light generating devices 1000, and the optics 200, are configured to generate nl first beams 1110 of first light 1111, wherein the nl first beams 1110 of first light 1111 integrated over time spatially overlap, wherein nl>3. Here, all beams 1110 of first light 1111 originate from a single source 10. They also may essentially follow the same optical path downstream of the radiation exit window 105. Hence, integrated over time the different beams, having e.g. different polarization diversity and/or angular diversity, may spatially overlap.

A very compact configuration that electronically generates 2 independent modes is shown in Fig. 7. This figure schematically depicts an embodiment of a relatively compact configuration to electronically generate 2 independent modes. A laser beam passes a polarization switch. The laser beam enters a polarizing beam splitter with two (weakly) diffusely reflecting facets RD1 and RD2. Light in the p-state passes the polarizing beam splitting coating and reflects from reflective diffuser 1. It again passes the coating towards the light exit. Light in the s-state reflects from the coating, reflects from reflective diffuser 2, reflects again from the coating and finds its way to the light exit. An advantage may be that only one polarization switch is needed. In this way a very compact architecture may be obtained.

Referring to Fig. 7, a laser light beam may be directed through the polarization switch PS. Here the state of polarization can be switched from p to s or vice versa. The switch can be a single pixel half-wave retarder liquid crystal cell or a multipixel device such as used in digital projectors. The laser light enters a polarizing beam splitter BS and depending on the polarization state, the light beam passes the polarization dependent coating (p-state) or reflects from the coating (s-state). In the figure, as an example, a solid arrow shows the path of e.g. p-state light, and the dashed arrow the s-state. P-state light subsequently may reflect from a diffuse facet (lower dashed side) of the polarizing beam splitter, passes the polarizing coating again and exits the device.

S-state light, however, reflects from the coating towards diffuser facet (upper dashed side). The scattered s-state light may be reflected from the polarizing coating and exits the device at the same location as the p-state light. The polarizing coating first splits the light and then combines it again.

Would the polarization switch be a single pixel half-wave retarder, two independent speckle modes can be generated. Would the polarization switch be less or more than a half wave retarder, a mix of two patterns may be generated in a degree that may depend on the polarization state after the retarder (e.g. 50%-50% for circularly polarized light), after a 45° retarder. Would the polarization switch PS be a multi-pixel half-wave retarder, a multitude of independent speckle modes may be generated.

Two or more devices can be operated in series to generate a multitude of independent speckle modes.

Reference RD indicates a reflective diffusor, which may be facets.

Fig. 8a schematically depicts an embodiment wherein at least 3 of the kl first beams of first light 1111 have mutually different centroid wavelengths within a range of 0.1- 100 nm. Here, five beams of first light with different centroid wavelengths, indicated with 1- 5 are depicted. These may be beams of kl lasers. Second light generation device light 1201 and third light generation device light 1301 are e.g. single beams, such as of a single laser.

Fig. 8a in fact also schematically depicts an embodiment wherein the first light of one or more first beams of first light have a first type of color, wherein the first light of one or more other first beams of first light have a second type of color, and wherein the first light of at least two yet other first beams of first light have a third type of color, and wherein the first light of at least two yet other first beams of first light have centroid wavelengths within a range of 0-50 nm, and wherein in the first operational mode the control system is configured to generate the first system beam of white first system light.

Fig. 8b schematically displays five overlapping spots. More or less overlap may be possible.

Fig. 8c schematically depicts on the left a plurality of different diffusor configurations 140. Here, a diffusor is applied with different areas with different diffusing behavior. By shifting the diffusor or by positioning beams (see dashed circles) at different positions, a plurality of different diffusor configuration may be obtained, leading to angular diversity.

Fig. 8c schematically depicts on right left a plurality of different polarization configurations 150. Here, a polarizer is applied with different areas with different polarization behavior. By shifting the polarizer or by positioning beams (see dashed circles) at different positions, a plurality of different polarization configurations 150 may be obtained, leading to polarization diversity.

Fig. 9 schematically depicts embodiments of a lamp 1, a luminaire 2, or projector device 3, comprising the light generating system 100 as described herein. Fig. 9 schematically depicts an embodiment of a luminaire 2 comprising the light generating system 100 as described above. Reference 301 indicates a user interface which may be functionally coupled with the control system 300 comprised by or functionally coupled to the lighting system 100. Fig. 9 also schematically depicts an embodiment of lamp 1 comprising the light generating system 100. Reference 3 indicates a projector device or projector system, which may be used to project images, such as at a wall. The lamp 1, luminaire 2, or projector device 3 are indicated with the general reference 1200.

Referring to Fig. 9, the beams may overlap at least at the target, which could be in the far field (or alternatively in the near field). Here, some examples of far field are schematically depicted.

Hence, amongst others the invention provides a laser based light source with adjustable sparkling using in specific embodiments multiple lasers, especially in embodiments a laser based white light source with adjustable sparkling using in specific embodiments multiple lasers.

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” also includes 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.