Tunable constant power dual laser-phosphor engine with single laser wavelength

Abstract

The invention provides a light generating system (1000) comprising a first light generating device (110), a second light generating device (120), a luminescent material (200), a control system (300), optics (500), a polarization control system (600), a diffuser system (1710), and a light exit (1090); wherein: in a first operational mode of the light generating system (1000), the first light generating device (110) is configured to provide first device light (111) with a first radiant flux Pl, and the second light generating device (120) is configured to provide second device light (121) with a second radiant flux P2, wherein one of the first radiant flux Pl and the second radiant flux P2 is at least 5% larger than the other one of the first radiant flux Pl and the second radiant flux P2; the luminescent material (200) is configured to convert at least part of the first device light (111) and / or at least part of the second device light (121) received by the luminescent material (200) into luminescent material light (201); the diffuser system (1710) comprises a diffuser (710); wherein the diffuser system (1710) is configured to diffuse at least part of the first device light (111) and / or at least part of the second device light (121) received by the diffuser system (1710) into diffused device light (711); the optics (500) comprise redirection optics (510); wherein the redirection optics (510) comprise a first polarization based redirection optics (PBS1) and a second polarization based redirection optics (PPBS2); the light generating system (1000) is configured to generate system light (1001); the control system (300) is configured to control a spectral power distribution of the system light (1001); and in the first operational mode of the light generating system (1000) the system light is white light (1001) comprising at least part of the luminescent material light (201) and at least part of the diffused device light (711).

Description

[0001] Tunable constant power dual laser-phosphor engine with single laser wavelength

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a light generating system. The invention further relates to a lighting device comprising the light generating system.

[0004] BACKGROUND OF THE INVENTION

[0005] Laser-phosphor based lighting fixtures are known in the art. For instance, WO2022143318 describes a light emitting device, comprising a first light source, a second light source, a dichroic mirror, a wavelength conversion apparatus, a first light path adjusting apparatus or a second light path adjusting apparatus, and a first scattering optical system. The light mixing effect of emergent light can be improved by using the first scattering optical system. Light emitted by the first light source is all used for exciting the wavelength conversion apparatus.

[0006] WO2018 / 196195A1 discloses a light source system having a light source device, a first light splitting and combining device, a wavelength converter and a light processing device. The light source device issues first excitation light and second excitation light, the first excitation light having a first polarization state, and the second excitation light having a second polarization state that is different from first polarization state. The first light splitting and combining device comprises at least one transparent substrate guiding excitation light in a first preset proportion among the second excitation light to the light processing device, and guides another part of the excitation light to the wavelength converter. The light processing device scatters the received excitation light and emits third excitation light. The wavelength converter converts the received excitation light into excited light. The third excitation light and the excited light are guided to a light-emitting channel.

[0007] US2022 / 011659A1 discloses a light source apparatus including light sources emitting first and second polarized light, an optical element transmitting one of the polarized light and reflecting the other, a polarization rotator generating polarization rotated light from the first polarized light, a wavelength convertor converting the second polarized light into wavelength converted light, and a controller. The optical element generates emitted light by combining the wavelength converted light and polarization rotated light. The controller acquires respective deterioration amounts of the light sources, and controls, based on respective changes in light emission amounts from the light sources acquired from the deterioration amounts, the light emission amount from at least one of the light sources for making different respective change amounts of the light emission amounts from the light sources, or changing a ratio between respective light emission amounts from the light sources.

[0008] SUMMARY OF THE INVENTION

[0009] High brightness light sources can be used in various applications including spots, stage-lighting, headlamps, home and office lighting, and automotive lighting. For this purpose, laser-phosphor technology can be used, wherein a laser provides laser light and a remote phosphor converts laser light into converted light. A relatively straightforward way to produce white light using lasers is to use (blue) laser light in combination with a (yellow) phosphor to generate phosphor converted light. Laser-phosphor systems may allow generation of high brightness light and may therefore be used in projection systems, including displays such as cinema projectors and projectors for home, school, and office applications, car front lighting, search lighting, stage lighting, architectural lighting, and special lighting applications. In many cases, however, the light engine may be capable to generate only a single color point as defined by the luminescent converter. Creation of a product range providing different color points may in this case be costly as it may require multiple unique components to be designed, qualified, produced, and kept in stock. In other cases, e.g. in RGB LCD-based projection systems, the maximum brightness may be limited by the components used, the engine volume may be large due to the many components, and the system cost may be high due to the many dedicated components.

[0010] An option to combine pump-light and luminescent light may be to use a polarizing beam splitter for the pump light, by which part of the light may be reflected to the luminescent material and part may be transmitted to a diffuser. However, it appears that the diffused light may to a large degree be depolarized, resulting in relatively high losses of diffused blue light at the beam combiner where it is combined with the luminescent light into white output light. In addition, using a single laser source (that may comprise multiple laser diodes) may significantly limit the maximum output power due to size limitations to the optical components. Therefore, laser phosphor sources comprising two laser banks may be of high interest, e.g. for entertainment lighting. Various configurations can be proposed using e.g. two blue laser light sources. In a first possible configuration, one of the laser sources may be fully used to pump a luminescent material and the other may be partly used to pump that same luminescent material and partly be used to be diffused after which this is used to contribute to the white output light. In this way, more than the output power of a single laser sources can be used for luminescent conversion, while part of a laser source may be used to contribute as blue light to the output white light. However, if two laser beam of substantially the same wavelength are combined by a polarizing beam splitter, then both sources may need to have orthogonal (linear) polarizations. This may be very suitable for a system that only needs to provide a single color point of the output light. However, for systems that have a selectable output CCT, generally a more complex configuration may have to be chosen to enable this. While it may be desirable to use the blue channel in a diffuse reflective mode, this may impact the blue channel efficiency.

[0011] 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 abovedescribed 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.

[0012] According to a first aspect, the invention provides a light generating system (“system”) comprising a first light generating device, a second light generating device, a luminescent material, a control system, optics, a polarization control system, a diffuser system, and a light exit. Especially, each of the light generating devices (110,120) comprise a solid-state light source. In embodiments, the solid state light sources may be selected from the group of diode lasers, superluminescent diodes, and multi -junction diodes. Further, in embodiments the first light generating device is configured to provide first device light having a first centroid wavelength (kci). Yet, in embodiments the second light generating device is configured to provide second device light having a second centroid wavelength (Xc2). In embodiments, in a first operational mode of the light generating system, the first light generating device may be configured to provide first device light with a first radiant flux Pl, and the second light generating device may be configured to provide second device light with a second radiant flux P2. Especially, in embodiments one of the first radiant flux Pl and the second radiant flux P2 may be larger than the other one of the first radiant flux Pl and the second radiant flux P2, such as at least about 5% larger. In embodiments, the luminescent material may be configured to convert at least part of the first device light and / or at least part of the second device light received by the luminescent material into luminescent material light. Further, in embodiments the diffuser system may comprise a diffuser. Especially, the diffuser system may be configured to diffuse at least part of the first device light and / or at least part of the second device light received by the diffuser system into diffused device light. Further, in embodiments the optics may comprise redirection optics. Especially, in embodiments the redirection optics may comprise a first polarization based redirection optics (PBS1) and a second polarization based redirection optics (PPBS2). In specific embodiments, the first polarization based redirection optics (PBS1) may be configured to direct first device light and second device light received by the first polarization based redirection optics (PBS1) in an optical path to the second polarization based redirection optics (PPBS2). Further, in embodiments the first device light received by the first polarization based redirection optics (PBS1) may comprise first linear polarized light. Yet, in embodiments the second device light received by the first polarization based redirection optics (PBS1) may comprise second linear polarized light. Especially, in embodiments the first linear polarized light and the second linear polarized light may have orthogonal (linear) polarizations. In embodiments, the polarization control system may be configured to control a polarization of device light propagating from the first polarization based redirection optics (PBS1) to the second polarization based redirection optics (PPBS2). In embodiments, the second polarization redirection optics (PPBS2) may be (i) partly reflective and partly transmissive for s-polarized device light and transmissive for p-polarized light received by the second polarization redirection optics (PPBS2), or may be (ii) partly reflective and partly transmissive for p-polarized light and reflective for s-polarized light received by the second polarization redirection optics (PPBS2). Yet, in embodiments the second polarization redirection optics (PPBS2) may be configured to direct device light received by the second polarization redirection optics (PPBS2) (during the first operational mode) in an optical path to the luminescent material and / or the diffuser system in dependence of a polarization of the device light. Yet, in embodiments the second polarization redirection optics (PPBS2) may (also) be configured to direct luminescent material light and diffused device light received by the second polarization redirection optics (PPBS2) in an optical path to the light exit. Especially, the light generating system may be configured to generate system light. In embodiments, the control system may be configured to control a spectral power distribution of the system light. In specific embodiments, in the first operational mode of the light generating system the system light may be white light comprising at least part of the luminescent material light and at least part of the diffused device light. Further, in specific embodiments, in the first operational mode of the light generating system the system light may have a correlated color temperature of at least 5000 K. Hence, in specific embodiments the invention provides a light generating system comprising a first light generating device, a second light generating device, a luminescent material, a control system, optics, a polarization control system, a diffuser system, and a light exit; wherein: (A) each of the light generating devices comprise a solid-state light source selected from the group of diode lasers, superluminescent diodes, and multi -junction diodes; wherein the first light generating device is configured to provide first device light having a first centroid wavelength (Xci), and wherein the second light generating device is configured to provide second device light having a second centroid wavelength (Xc2); (B) in a first operational mode of the light generating system, the first light generating device is configured to provide first device light with a first radiant flux Pl, and the second light generating device is configured to provide second device light with a second radiant flux P2, wherein one of the first radiant flux Pl and the second radiant flux P2 is at least 5% larger than the other one of the first radiant flux Pl and the second radiant flux P2; (C) the luminescent material is configured to convert at least part of the first device light and / or at least part of the second device light received by the luminescent material into luminescent material light; (E) the diffuser system comprises a diffuser; wherein the diffuser system is configured to diffuse at least part of the first device light and / or at least part of the second device light received by the diffuser system into diffused device light; (F) the optics comprise redirection optics; wherein the redirection optics comprise a first polarization based redirection optics (PBS1) and a second polarization based redirection optics (PPBS2); (G) the first polarization based redirection optics (PBS1) is configured to direct first device light and second device light received by the first polarization based redirection optics (PBS1) in an optical path to the second polarization based redirection optics (PPBS2); wherein the first device light received by the first polarization based redirection optics (PBS1) comprises first linear polarized light, wherein the second device light received by the first polarization based redirection optics (PBS1) comprises second linear polarized light, wherein the first linear polarized light and the second linear polarized light have orthogonal (linear) polarizations; (H) the polarization control system is configured to control a polarization of device light propagating from the first polarization based redirection optics (PBS1) to the second polarization based redirection optics (PPBS2); (I) the second polarization redirection optics (PPBS2) is (i) partly reflective and partly transmissive for s-polarized device light and transmissive for p-polarized light received by the second polarization redirection optics (PPBS2), or is (ii) partly reflective and partly transmissive for p-polarized light and reflective for s-polarized light received by the second polarization redirection optics (PPBS2); the second polarization redirection optics (PPBS2) is configured to direct device light received by the second polarization redirection optics (PPBS2) (during the first operational mode) in an optical path to the luminescent material and (to) the diffuser system in dependence of a polarization of the device light; the second polarization redirection optics (PPBS2) is (also) configured to direct luminescent material light and diffused device light received by the second polarization redirection optics (PPBS2) in an optical path to the light exit; (J) the light generating system is configured to generate system light; the control system is configured to control a spectral power distribution of the system light; and (K) in the first operational mode of the light generating system the system light is white light comprising at least part of the luminescent material light and at least part of the diffused device light, and, in embodiments having a correlated color temperature of at least 5000 K, such as in embodiments wherein the CCT is selected from the range of 6000-8000 K (though other CCTs may also be possible).

[0013] With such system, the spectral power distribution may be controllable.

[0014] Further, the system may be relatively compact and may comprise a relatively low number of optical components. Yet, high intensity light may be provided. This invention may provide a solution for the efficiency problem of the reflectively diffused blue light channel in combination with an extremely compact and low parts-count configuration that may be capable of providing CCT-tunable output light based on two laser banks that may in embodiments emit at the same wavelength. Yet further, with such a system the color point may easily be adjusted by the user, for any of the color points selected in a predetermined range of white light output color points (e.g. 5000-10000 K, like 6000-10000 K), while providing highly efficient collection of all the spectral contributions to the output light, resulting in a relatively high efficiency high brightness and high flux (>40 klm) white light engine. Hence, the invention may provide a constant power tunable CCT laser-phosphor source comprising only two laser banks. This approach may also or specifically be used to calibrate the color point of the system output light. With the proposed 2-channel approach, in embodiments the output CCT can be fine-tuned in the factory to a targeted value, which may lead to much better defined products. Further, this approach may enable a full use of all installed laser diodes. In general, laser banks may only be available with a limited variation in laser diode count. Would we not have the herein proposed tuning option, then a required CCT may only be achieved by reducing the overall laser power in one of two color channels. Though such tuning is not excluded herein, in embodiments of the invention this may not be necessary, as tuning via the laser power can be prevented. Hence, amongst others, the invention provides a tunable, optionally constant power, dual laser-phosphor engine with single laser wavelength. As indicated above, in embodiments the light generating system may comprise a first light generating device, a second light generating device, a luminescent material, a control system, optics, a polarization control system, a diffuser system, and a light exit. Embodiments thereof will be further described below.

[0015] The light generating devices may be configured to generate device light. Therefore, in embodiments, the light generating devices may each comprise a solid-state light source. In embodiments, the light generating devices may comprise (at least) a first light generating device, a second light generating device, and a third light generating device. The first light generating device may, in embodiments, be configured to generate first device light. Therefore, in embodiments, the first light generating device may comprise a first light source. The first light source may be essentially any light source, see also further below. Especially, in embodiments, the (first light source of the) first light generating device may comprise a first solid state light source. Hence, in embodiments, the first light generating device may comprise one or more of a laser diode, a superluminescent diode, and a stacked multi -junction light-emitting diode (LED). The first light generating device may herein also comprise a plurality of first (solid state) light sources. Especially, in specific embodiments, the first light generating device may comprise a first laser bank comprising a plurality of first lasers. A laser bank may comprise a relatively dense assembly of multiple laser diodes on a shared substrate provided with collimating optics, such as collimating lenses comprising one lens per laser diode (e.g. arranged in an array of lenses, see also further below). The use of laser banks may especially be convenient for projecting a beam of high power laser light onto a luminescent converter without the need for using an inverse beam expander. Further, in embodiments, the first light generating device may especially be configured to generate first device light having a first centroid wavelength (Xci). Especially, in embodiments, the first device light may have a first centroid wavelength (Xci) selected from the wavelength range of 400-500 nm, like selected from the wavelength range of 430-500 nm, such as from the range of 440-490 nm, like from the range of 445-480 nm. Hence, in embodiments, the first device light may be blue light.

[0016] Analogously to the first light generating device, in embodiments, the second light generating device may be configured to generate second device light. Therefore, in embodiments, the second light generating device may comprise a second light source. The second light source may be essentially any light source, see also further below. Especially, in embodiments, the (second light source of the) second light generating device may comprise a second solid state light source. Hence, in embodiments, the second light generating device may comprise one or more of a laser diode, a superluminescent diode, and a stacked multijunction light-emitting diode (LED). In embodiments, the second light generating device may comprise essentially the same light generating device as the first light generating device. However, in other embodiments, the first light generating device and the second light generating device may be substantially different. The second light generating device may herein also comprise a plurality of second (solid state) light sources. Especially, in specific embodiments, the second light generating device may comprise a second laser bank comprising a plurality of second lasers. Further, in embodiments, the second light generating device may especially be configured to generate second device light having a second centroid wavelength ( c2). Especially, in embodiments, the second device light may have a second centroid wavelength ( c2) selected from the wavelength range of 430-500 nm, such as from the range of 400-500 nm, like selected from the wavelength range of 440-490 nm, like from the range of 445-480 nm. Hence, in embodiments, the second device light may be blue light.

[0017] Hence, in embodiments each of the light generating devices may comprise a solid-state light source selected from the group of diode lasers, superluminescent diodes, and multi -junction diodes. Further, in embodiments the first light generating device may be configured to provide first device light having a first centroid wavelength (Xci), and the second light generating device may be configured to provide second device light having a second centroid wavelength ( c2). Further, in specific embodiments the first centroid wavelength (Xci) and the second centroid wavelength ( c2) may be individually selected from the wavelength range of 400-490 nm, more especially selected from the wavelength range of 440-490 nm. In specific embodiments, |XC2-Xci| < 50 nm. More especially, in embodiments |Xc2-Xci| < 10 nm. Hence, in specific embodiments 0 nm < |XC2-Xci| < 10 nm. In specific embodiments, Xci=Xc2. When the centroids wavelengths are essentially the same, like |XC2-Xci| < 10 nm, more especially |Xc2-Xci| < 5 nm solid state light sources from the same wavelength bin may be applied. This may improve reliability and / or reproducibility. Hence, in embodiments the light generating devices may be selected from the same wavelength bin or comprise solid state light sources selected from the same wavelength bin.

[0018] The term “centroid wavelength”, also indicated as Xc, 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 Xc = X X*I(X) / (X I(X), where the summation is over the wavelength range of interest, and I(X) 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.

[0019] In embodiments, in a first operational mode of the light generating system, the first light generating device is configured to provide first device light with a first radiant flux Pl, and the second light generating device is configured to provide second device light with a second radiant flux P2, wherein one of the first radiant flux Pl and the second radiant flux P2 may be at least 5% larger than the other one of the first radiant flux Pl and the second radiant flux P2. Hence, in embodiments P2 / Pl>1.05 or P2 / Pl<0.95. The differences in radiant fluxes between the two sources of light allow a broader tunability of the spectral power distribution of the system light (generated by the light generating system) (as will also be further described below). The ratio of the radiant fluxes may be set or controlled in different ways, see further also below. Further, there may be more than a single (series ol) operational mode, see further also below.

[0020] Further, the luminescent material may especially be configured to convert at least part of the first device light and / or at least part of the second device light received by the luminescent material into luminescent material light. Yet further, the diffuser system may in embodiments comprise a diffuser. Especially, the diffuser system may in embodiments be configured to diffuse at least part of the first device light and / or at least part of the second device light received by the diffuser system into diffused device light. As the second polarization based redirection optics may in general reflect at least part of one of the linear polarizations, and the device light reaching the first polarization based redirection optics may be orthogonally be polarized, in the first operational mode the luminescent material may convert at least part of the first device light and at least part of the second device light received by the luminescent material into luminescent material light.

[0021] Likewise, in embodiments in the first operational mode the diffuser system may diffuse at least part of the first device light and at least part of the second device light, received by the diffuser system, into diffused device light. Therefore, in embodiments (a) the luminescent material may especially be configured to convert at least part of the first device light and at least part of the second device light, received by the luminescent material, into luminescent material light, and (b) the diffuser system may be configured to diffuse at least part of the first device light and at least part of the second device light, received by the diffuser system, into diffused device light.

[0022] As indicated above, in embodiments the optics may comprise redirection optics. Especially, in embodiments the redirection optics may comprise a first polarization based redirection optics (PBS1) and a second polarization based redirection optics (PPBS2). Redirection optics may be applied to combine light propagating along two different optical paths in a single optical path. Especially, two orthogonal propagating beams of light, received by the first redirection optics, may be combined in a single beam of light.

[0023] In embodiments, the redirection optics may be polarization based. Hence, e.g. a beam of s-polarized light and a beam of p-polarized light may be combined into a beam of light comprising both polarizations, i.e. light that can generally be described as elliptically polarized light (note that this may include the extremes of circular polarized light as well as linear polarized light).. For instance, one of the beams may be transmitted, and one of the beams may be reflected. The combined beam may propagate in the same direction as one of the transmitted beam and reflected beam. Hence, the redirection optics may comprise a polarized beam combiner. Such optics, however, may also be used to split a beam of light. Especially, a single beam of light comprising both polarizations, received by the redirection optics, may be split into two orthogonal propagating beams of light. Hence, in embodiments, the redirection optics may be polarization based. Hence, e.g. a beam of elliptically polarized light may be split in two (orthogonal) beams of s-polarized light and p-polarized light. For instance, one of the polarizations may be transmitted, and one of the polarizations may be reflected. This may also imply that a beam of light that consists of essentially linear polarized light may be (at least partly) reflected or (at least partly) transmitted at the polarization based redirection optics. Hence, the redirection optics may comprise a polarized beam splitter. Such optics, however, may thus also be used to combine beams of light. Hence, the herein described polarization based redirection optics are herein also indicated as polarization beam combiners, or polarizing beam combiners, or polarization beam splitters, or polarizing beam splitters, and are shortly indicated as “PBS”.

[0024] A first polarizing beam splitter may be used to combine the first device light and second device light. Hence, this may imply that the first device light reaching the first polarizing beam splitter and the second device light reaching the first polarizing beam splitter have different polarizations. One may be s-polarized and the other one may be p-polarized. One may be elliptically polarized, and the other one may be s-polarized or p-polarized. Especially, however, the second device light and first device light differ in polarization, like s-polarized light and p-polarized light, or both elliptically polarized, but one more s- polarization than p-polarization, and the other one more p-polarization than s-polarization. Further, in embodiments the first device light reaching the first polarizing beam splitter and the second device light reaching the first polarizing beam splitter (having different polarizations) may be orthogonally incident on the first polarizing beam splitter. Especially, in embodiments the optical exes of the first device light reaching the first polarizing beam splitter and the second device light reaching the first polarizing beam splitter may both have angles of incidence of 45° (although other angles are herein not excluded). In embodiments, the angles of incidence of 45° may especially refer to angles of incidence of 45°±5°, more especially 45°±2°, such as 45°±1°. Hence, when combining two beams, these beams may essentially propagate in an orthogonal direction on the beam combiner and be incident thereon (orthogonally).

[0025] Especially, in embodiments, the first polarizing beam splitter may be configured to transmit (or reflect) at least 60%, such as at least 70%, like at least 80% of the light (comprising the first linear polarization) received by the first polarizing beam splitter. Especially, in embodiments, the first polarizing beam splitter may be configured to transmit (or reflect) at least 90%, more especially at least 95%, including 100% of the light (comprising the first linear polarization) received by the first polarizing beam splitter. Further, in such embodiments, the first polarizing beam splitter may be configured to reflect (or transmit) light received by the first polarizing beam splitter and (said (device) light) comprising a second linear polarization. Especially, in embodiments, the first polarizing beam splitter may be configured to reflect (or transmit) at least 60%, such as at least 70%, like at least 80% of the light (comprising the second linear polarization) received by the first polarizing beam splitter. Especially, in embodiments, the first polarizing beam splitter may be configured to reflect (or transmit) at least 90%, more especially at least 95%, including 100% of the light (comprising the second linear polarization) received by the first polarizing beam splitter. Note that, in embodiments, the first polarizing beam splitter may herein especially function as a beam combiner. Especially, in embodiments, the first polarizing beam splitter may be configured to combine (along a same optical path) at least a part of the first device light with at least a part of the second device light into combined light. Such percentage may refer to the percentage of the radiant flux (received by the first polarizing beam splitter (especially under 45° angle with a normal of the plane of incidence of the element)). Hence, in embodiments, a polarizing beam splitter may especially be configured to split light received by the polarizing beam splitter into orthogonal beams of light having different (orthogonal) polarization. The polarizing beam splitter may especially do so upon irradiation at an about 45° angle. Additionally or alternatively, in embodiments, a polarizing beam splitter may be configured to combine light received by the polarizing beam splitter from orthogonal beams of light and having different (orthogonal) (linear) polarizations into a same optical path.

[0026] The first device light may be polarized light or a polarization may be imposed to the first device light, e.g. with a polarizer. Hence, the first device light reaching the first polarizing beam splitter may comprise polarized light. Likewise, the second device light may be polarized light or a polarization may be imposed to the second device light, e.g. with a polarizer. Hence, the second device light reaching the first polarizing beam splitter may comprise polarized light. The first polarization based redirection optics may be used to combine these beams and direct a combined beam of device light to the second polarization based redirection optics. Therefore, in embodiments the first polarization based redirection optics (PBS1) may be configured to direct first device light and second device light received by the first polarization based redirection optics (PBS1) in an optical path to the second polarization based redirection optics (PPBS2). Especially, in embodiments the first device light received by the first polarization based redirection optics (PBS1) may comprise first linear polarized light, and the second device light received by the first polarization based redirection optics (PBS1) may comprise second linear polarized light, wherein the first linear polarized light and the second linear polarized light have orthogonal (linear) polarizations. Hence, first polarization based redirection optics may comprise or be a (first) polarizing beam splitter. Note that the first polarization based redirection optics may essentially be used as beam combiner. Hence, the (first) polarizing beam splitter may also be indicated a “polarizing beam combiner”. In fact, this may apply to other polarizing beam splitters as well.

[0027] As indicated above, the first device light may comprises first linear polarized light and the second device light may comprises second linear polarized light. Hence, in embodiments the first device light, received by the first polarization based redirection optics (PBS1), may be elliptically polarized and / or the second device light, received by the first polarization based redirection optics (PBS1), may be elliptically polarized light. In embodiments, when both being elliptically polarized, the main axis may be configured orthogonal. Yet, in embodiments the first device light, received by the first polarization based redirection optics (PBS1), may be essentially be linearly polarized and / or the second device light, received by the first polarization based redirection optics (PBS1), may be essentially be linearly polarized light (with orthogonal linear polarizations).

[0028] In embodiments, the device light received by the first polarizing beam splitter may especially be polarized light. Hence, in embodiments, the light generating system may be configured such that (both) the first device light and( / or) the second device received by the first polarizing beam splitter may comprise polarized light. The phrase “... light received by ...”, and similar phrases, such as “device light received by the first polarizing beam splitter” may especially indicate that when the light is actually received by an item, an action may take place. The action may in embodiments be one or more of conversion, reflection, and transmission. Further, the action may also include refraction. Whether or not such item receives light may e.g. depend on e.g. a controlling mode (for instance whether or not a light generating device provides light).

[0029] In embodiments, the second linear polarization may especially be different from the first linear polarization. Especially, in some embodiments the first linear polarization may be p-polarization and the second linear polarization may be s-polarization. In other embodiments, the first polarization may be s-polarization and the second polarization may be p-polarization. Herein, the terms “p-polarization” and “s-polarization” may especially refer to the polarization of light when incident on (a light-receiving plane ol) the lightreceiving element, such as e.g. the first polarization based redirection optics (especially the first polarizing beam splitter).

[0030] Hence, in embodiments the first device light and the second device light reaching the first polarization based redirection optics may have essentially orthogonal polarizations. Hence, in embodiments the first device light reaching the first polarization based redirection optics may essentially be p-polarized light and the second device light reaching the first polarization based redirection optics may essentially be s-polarized light, or the first device light reaching the first polarization based redirection optics may essentially be s-polarized light and the second device light reaching the first polarization based redirection optics may essentially be p-polarized light. Hence, when both the first light generating device and the second light generating device are operating, first device light and second device light, combined by the first polarization based redirection optics, may propagate to the second polarization based redirection optics.

[0031] The spectral power distribution of the system light may be controlled in several ways. Especially, a polarization control system may be applied (that may be controlled by the control system), and which may be configured to one or more of (i) controlling an orientation of the light generating devices (and the first polarization based redirection optics) relative to the second polarization based redirection optics, and (ii) controlling an orientation of a polarization rotator (configured downstream of the first polarization based redirection optics) relative to the second polarization based redirection optics. Hence, in embodiments the polarization control system may be configured to control a polarization of device light propagating from the first polarization based redirection optics (PBS1) to the second polarization based redirection optics (PPBS2). To this end, the system may comprise one or more movement devices, which may be configured to move one or more of (a) the light generating devices and (b) the polarization rotator. A movement device may be configured to translate or rotate (including being able to translate and rotate), and may include a translational actuator or a rotary actuator, such as for moving above indicated item(s). Especially, herein rotation, of (a) the light generating devices (and / ) or (b) the polarization rotator, may be applied (for controlling the spectral power distribution).

[0032] 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”.

[0033] As indicated above, the first polarization based redirection optics (PBS1) may be configured to direct first device light and second device light received by the first polarization based redirection optics (PBS1) in an optical path to the second polarization based redirection optics (PPBS2). Hence, the second polarization based redirection optics is configured downstream of the first polarization based redirection optics. The second polarization based redirection optics may thus receive device light, which may comprise one or more of first device light and second device light. The second polarization based redirection optics may have multiple functions. One function may be to direct device light dependent upon its polarization to the luminescent material or to the diffuser system. Hence, this may be a splitting function. However, the second polarization based redirection optics may also be configured to receive luminescent material light and diffused device light, respectively, and direct these in an optical path to the light exit. Hence, this may be a combining function. To this end, in embodiments the second polarization redirection optics (PPBS2) is (i) partly reflective and partly transmissive for s-polarized device light and transmissive for p-polarized light received by the second polarization redirection optics (PPBS2), or is (ii) partly reflective and partly transmissive for p-polarized light and reflective for s-polarized light received by the second polarization redirection optics (PPBS2). Hence, in first embodiments s-polarized light received by the second polarization redirection optics may partly be reflected and partly be transmitted by the second polarization redirection optics. Further, in (such) first embodiments p-polarized light may at least partly, more especially, essentially be transmitted by the second polarization redirection optics. However, in second embodiments, p-polarized light received by the second polarization redirection optics may partly be reflected and partly be transmitted by the second polarization redirection optics. Further, in (such) second embodiments s-polarized light may at least partly, more especially, essentially be reflected by the second polarization redirection optics.

[0034] As indicated above, the second polarization redirection optics (PPBS2) may be configured to direct device light received by the second polarization redirection optics (PPBS2) (during the first operational mode) in an optical path to the luminescent material and / or (to) the diffuser system in dependence of a polarization of the device light. Further, as indicated above, the second polarization redirection optics (PPBS2) is (also) configured to direct luminescent material light and diffused device light received by the second polarization redirection optics (PPBS2) in an optical path to the light exit.

[0035] Note that when both the first light generating device and the second light generating device are in operation, part of the device light received by the second polarization redirection optics may be directed to the luminescent material and another part of the device light received by the second polarization redirection optics may be directed to the diffuser system. Especially, this may be due to the fact that the second polarization redirection optics comprises a partial polarization beam splitter (PPBS) which is either (i) partly reflective and partly transmissive for s-polarized device light or (ii) partly reflective and partly transmissive for p-polarized light. Hence, in embodiments the second polarization redirection optics (PPBS2) may be configured to direct device light received by the second polarization redirection optics (PPBS2) (during the first operational mode) in an optical path to the luminescent material and the diffuser system in dependence of a polarization of the device light. Which part of the device light is directed to the luminescent material and which part of the device light is directed to the diffuser system depends upon the polarization of the device light received by the second polarization redirection optics. However, would (for the sake of argument) only one of the first light generating device and the second light generating device be in operation, at least part of the device light received by the second polarization redirection optics may be directed to the luminescent material and / or at least part of the device light received by the second polarization redirection optics may be directed to the diffuser system, including embodiments wherein, dependent upon the polarization of the device light received by the second polarization redirection optics, only one of the luminescent material and the diffuser system could receive (that) device light via the second polarization redirection optics (i.e. only one of the light generating device might emit light and when the polarization of this light when arriving at second polarization based redirection optics would be fully s- or p-polarized. Especially, in in the first operational mode, however, both the first light generating device and second light generating device are in operation, which may lead to device light being incident (via the optics) on both the luminescent material and the diffuser, with, as indicated herein, with controllable ratio’s.

[0036] As indicated above, in relation to a polarization based redirection optics, a beam of elliptically polarized light may be split in two (orthogonal) beams of s-polarized light and p-polarized light. For instance, one of the polarizations may be transmitted, and one of the polarizations may be reflected (by the polarization based redirection optics). This may thus also imply that a beam of light that consists of essentially linear polarized light may be (at least partly) reflected or (at least partly) transmitted at the polarization based redirection optics. Especially, however, this may depend on a) the orientation of the plane of polarization relative to the plane of incidence onto the polarization based redirection optics, and b) on the type of polarization based redirection optics. For instance, it may depend on the presence of both s- and p-polarized components in the linear polarized incident light; if there is only one of them present, then the light may be reflected or transmitted for a fully polarizing beam splitter. Further, for instance, when a partially polarization based redirection optics is applied by definition at least one of s- and p- polarization are both reflected and transmitted.

[0037] As indicated above, the light generating system is configured to generate system light. Light escaping from the light exit may be indicated as system light. As indicated above, in embodiments the system light may comprise at least part of the luminescent material light and at least part of the diffused device light. Hence, the luminescent material light and the diffused device light may via an optical path between the second polarization redirection optics to the light exit escape from the system via the light exit. The light exit may comprise an opening or a last optical element, like a lens (including a lens array), a diffuser, etc.

[0038] In embodiments, the system light may, in an operational mode of the light generating system, be white light. Hence, the optics and light generating devices, as well controllable settings of the light generating devices and the optics may be selected such, that the system light is white light. Hence, in the first operational mode (see also below) of the light generating system the system light is white light comprising at least part of the luminescent material light and at least part of the diffused device light. In further specific embodiments, in the first operational mode of the light generating system the system light is white light comprising at least part of the luminescent material light and at least part of the diffused device light, and having a correlated color temperature of at least 5000 K. Further, in (other) embodiments, the system may be configured such that at least in one operational mode the system light is white light, for instance within about 7 SDCM (see also below) from the BBL. However, other operational modes may also be possible. Further, the control system may be configured to control a spectral power distribution of the system light.

[0039] Further, in embodiments the control system may be configured to control a radiant flux of the system light.

[0040] As indicated above, in embodiments, in a first operational mode of the light generating system, the first light generating device is configured to provide first device light with a first radiant flux Pl, and the second light generating device is configured to provide second device light with a second radiant flux P2, wherein one of the first radiant flux Pl and the second radiant flux P2 is larger than the other one of the first radiant flux Pl and the second radiant flux P2. For instance, P2 / Pl<0.98 or Pl / P2<0.98. The differences in radiant fluxes between the two sources in combination with the partial polarizing beam splitter allow tuning of the spectral power composition of the system light by rotating the light generating devices and / or a polarization rotator. For instance, in embodiments the correlated color temperature may be controllable over a relatively broad range.

[0041] The ratio of the radiant fluxes may be controlled in several ways. In a first line of embodiments, the radiant fluxes are kept constant but differ from each other. In such embodiments, the spectral power composition of the system light may be controlled by moving, especially rotating, the light generating devices and / or a polarization rotator relative to the second polarization redirection optics. In such first line of embodiments, the radiant fluxes may differ due to one or more of (i) using first and second light generating devices differing in the radiant flux they provide (e.g. at equal forward current), and (ii) using first and second light generating devices comprising different number of solid state light sources. Hence, in embodiments the first light generating device and the second light generating device may be operated in the first operational mode at constant power (while still allowing the spectral power distribution of the system light to be controllable (by controlling the polarization control system)). In a second line of embodiments, however, the radiant fluxes as such may be controlled by the control system, by controlling the forward current provided to the light generating devices. In the second line of embodiments, it may not be necessary to move, especially rotate, the light generating devices and / or a polarization rotator relative to the second polarization redirection optics, as by controlling the currents, the spectral power distribution of the system light may (already) vary. A combination of these lines of embodiments is also possible.

[0042] In the current invention, especially the first line of embodiments is further discussed.

[0043] As indicated above, in embodiments the radiant flux of the first device light may be at least 3%, like at least 5% larger than the radiant flux of the second device light, or vice versa. In specific embodiments, the difference may be larger, like at least 10%, up to even about four times as much. Hence, in embodiments (a) 1.05<P2 / Pl<4 or (b) 0.25<P2 / Pl<0.95 may apply. For instance, 1.1<P2 / PI<4 or (b) 0.25< P2 / Pi<0.9 may apply. More especially, in embodiments (a) 1.1<P2 / P1<2.86 or (b) 0.35<P2 / Pl<0.9 may apply. The differences in radiant fluxes may be achieved in several ways (see also above).

[0044] In embodiments, the first light generating device and the second light generating device are operated at respective forward currents such that the above indicated ratio’s, such as (a) 1.1<P2 / P1<2.86 or (b) 0.35<P2 / Pl<0.9, or other ratios, may be achieved.

[0045] In embodiments, the first light generating device may have a first rated forward current IRFI, the second light generating device may have a second rated forward current IRF2, and IRF2 / IRFI>1.05 or IRF2 / IRFI<0.95, or other ratios, (may apply). In embodiments, the first operational mode, the first light generating device may be operated at the first rated forward current IRFI, and the second light generating device may be operated at the second rated forward current IRF2. However, other forward currents of such light generating devices (during the first operational mode) are herein not excluded. Also in this way, the above indicated ratio’s, such as (a) 1.1<P2 / P1<2.86 or (b) 0.35<P2 / Pl<0.9, or other ratios, may be achieved.

[0046] In other embodiments, the first light generating device may have a first rated nominal (drive) current IRNFI, the second light generating device may have a second rated nominal (drive) current IRNF2, and IRNF2 / IRNFI>1.05 or IRNF2 / IRNFI<0.95, or other ratios, may apply. In embodiments, the first operational mode, the first light generating device may be operated at the first rated nominal (drive) current IRFI, and the second light generating device may be operated at the second peak rated forward current IRF2. However, other forward currents of such light generating devices (during the first operational mode) are herein not excluded. Also in this way, the above indicated ratio’s, such as (a) 1.1<P2 / P1<2.86 or (b) 0.35<P2 / Pl<0.9, or other ratios, may be achieved. In general, operation at forward currents larger than the rated nominal (drive) currents may be detrimental to (solid state based) light generating devices. Hence, in specific embodiments (in the first operational mode) the light generating devices (110,120) are operated at (rated) nominal (drive) currents. However, other embodiments may also be possible.

[0047] Hence, in embodiments light generating devices that may have essentially the same spectral power distribution may be operated at different forward currents. However, other embodiments may also be possible.

[0048] In other embodiments, the above indicated ratio’s, such as (a) 1.1<P2 / P1<2.86 or (b) 0.35<P2 / Pl<0.9, or other ratios, may be achieved by using assemblies of solid state light sources for the first light generating device and the second light generating devices, wherein the number of solid state light sources in the assemblies differ. However, in specific embodiments, all solid state light sources of assemblies may be of the same bin. Examples of suitable assemblies may be laser banks. Typically, the use of “laser banks”, being relatively dense assemblies of multiple laser diodes on a shared substrate that are commonly already provided with collimating lenses (typically in the form of a lens array comprising one lens per diode) may be convenient to project a beam of high power laser light onto a luminescent element without the need for using an inverse beam expander. In specific embodiments, a laser bank may therefore comprise an array of lenses (monolithic as multi-lens-array or as a set of discrete lenses). In such embodiments, individual lenses of the array of lenses may correspond with (or act on the individual laser beams from) individual lasers in the laser bank.

[0049] As beams of light emitted from such (multi-chip packages and / or) laser banks may comprise multiple narrow laser beams, each individual laser beam may represent a hot spot in the beam of device light. Focusing of such a beam of device light on e.g. a luminescent material may exceed the maximum tolerable local irradiance and result in damage to the luminescent material, or other materials present in the luminescent material arrangement. Therefore, in some embodiments, homogenizing optics may be applied and may especially be configured between (relative to the propagation of light through the system) the light generating devices (contributing to irradiation of the luminescent material) and collimating optics of the luminescent material, see also below. Similarly, in some embodiments, homogenizing optics may be applied and may especially be configured between (relative to the propagation of light through the system) the light generating devices (contributing to irradiation of the diffuser) and collimating optics of the diffuser, see also below. In embodiments, the homogenizing optics may e.g. comprise one or more of a transmissive volume diffuser, a transmissive surface diffuser, a reflective surface diffuser, a transmissive or reflective diffractive optical element, a transmissive holographic optical element, a single multi lens array, a double multi lens array such as a fly-eye lens array, or an integrating polygonal light pipe that may be either solid (with propagation in the integrator based on total internal reflection) or hollow (with propagation in the integrator based on specular reflection).

[0050] In embodiments, the condensing optics may comprise a first condensing optics configured (directly) upstream of the luminescent material and a second condensing optics configured (directly) upstream of the diffuser. Especially, in embodiments, the first condensing optics and the second condensing optics may each comprise at least one positive lens. In specific embodiments (such as e.g. when the luminescent material is configured in the reflective mode) the first condensing optics may comprise a first positive lens and a second smaller positive lens. In such embodiments, the smaller positive lens may especially be located between (relative to the propagation of light through the system) the first positive lens and the luminescent material or diffuser, respectively. Further, in embodiments, the optics may comprise a first collecting and collimating optics configured (directly) downstream of the luminescent material and a second collecting and collimating optics configured (directly) downstream of the diffuser. Especially, in embodiments, the first collecting and collimating optics and the second collecting and collimating optics may each comprise at least one positive lens, especially at least two positive lenses. In embodiments, the collimating optics and / or condensing optics, especially the lenses, may comprise glass materials, such as e.g. N-BK7, H-K51, B270, or fused silica (FS). The latter shows relatively low absorption and relatively low induced stress, but also has a relatively low refractive index. Therefore, if FS is used for all the lenses, in embodiments, the condensing optics for the reflective mode may preferably comprise three lenses.

[0051] Hence, in specific embodiments, the first light generating device may comprise a first laser bank comprising a plurality of first lasers, and the second light generating device comprises a second laser bank comprising a plurality of second lasers. Further, in specific embodiments the first laser bank comprises N1 first lasers, wherein the second laser bank comprises N2 second lasers, wherein in specific embodiments N2 / NI>1.05 or N2 / NI<0.95. For instance, in embodiments 1.05< N2 / NI<4 or (b) 0.25< N2 / NI<0.95 may apply. For instance, 1.1< N2 / NI<4 or (b) 0.25<N2 / NI<0.9 may apply. More especially, in embodiments (a) 1.1< N2 / NI<2.86 or (b) 0.35< N2 / NI<0.9 may apply. In this way, relatively broad ranges in CCT may be possible (see further also below). In embodiments, during the first operational mode, the first light generating device and the second light generating device may be operated at the rated forward currents (or the rated nominal (drive) currents), though other forward currents may also be possible. As indicated above, in specific embodiments, the first laser and the second lasers may essentially be the same (such as of the same wavelength bin (as indicated above, in specific embodiments Xci=Xc2)).

[0052] Note that an array of solid state light sources may provide multiple light generating devices, such as a first light generating device and a second light generating device. For instance, a subset of laser diodes of an array of laser diodes may be used as first light generating device, and its device light may at least partially follow another optical path than device light of another subset of laser diodes from that array (of laser diodes). Hence, in embodiments a single laser bank may be applied, of which the light is split in multiple portions, effectively providing multiple light generating devices. In general, this may imply the application of optics, allowing to divide the laser light of multiple subsets of lasers from the same bank into multiple their respective (separate) beams of light that at least partially do not have identical optical paths (in the light generating system). The subsets may comprise one or more of the laser diodes of the laser bank. However, especially a single laser diode may only be comprised by a single subset. Notwithstanding such embodiments, of course also multiple laser banks may be used to provide multiple light generating devices.

[0053] Getting back to the polarization redirection optics, especially the first polarization redirection optics may essentially be reflective for a first linear polarization and transmissive for a second linear polarization, wherein the first and second linear polarizations are selected from p-polarization and s-polarization. In specific embodiments, the first polarization redirection optics (PBS1) may be (i) at least 90% transmissive for first linear polarized light, and (ii) at least 90% reflective for second linear polarized light. The angle of incidence for the (orthogonal) beams of first device light and second device light may be 45°, though other angles are herein not excluded (see also above).

[0054] Further, in specific embodiments the second polarization redirection optics (PPBS2) may have (i) a transmittance for p-polarized device light of at least 90%, and a reflectance for s-polarized device light selected from the range of 20-80% (especially 30- 70%) (and a transmittance for s-polarized device light selected from the range of 80-20% (especially 70-30%)) for at least one of XC2 and Xci, or (ii) a reflectance for s-polarized device light of at least 90%, and a reflectance for p-polarized device light selected from the range of 20-80% (especially 30-70%) (and a transmittance for p-polarized device light selected from the range of 80-20% (especially 70-30%)) for at least one of XC2 and Xci. As indicated above, the angle of incidence for the beam of device light comprising one or more of first device light and second device light may be 45°, though other angles are herein not excluded (see also above).

[0055] Hence, in embodiments for the second polarization redirection optics (PPBS2), for light received at the second polarization redirection optics (PPBS2) having a first linear polarization the transmittance may be at least 90%, whereas for light received at the second polarization redirection optics (PPBS2) having a second linear polarization, orthogonal to the first linear polarization, may apply that it is partly transmitted, but with a smaller transmittance than for light having the first linear polarization, and partly reflected. Alternatively, in embodiments for the second polarization redirection optics (PPBS2), for light received at the second polarization redirection optics (PPBS2) having a first linear polarization the reflectance may be at least 90%, whereas for light received at the second polarization redirection optics (PPBS2) having a second linear polarization, orthogonal to the first linear polarization, may apply that it is partly reflected, but with a smaller reflectance than for light having the first linear polarization, and partly transmitted. In specific embodiments, the second polarization redirection optics (PPBS2) may (thus) have (i) a transmittance for p-polarized device light of at least 90%, and a reflectance for s-polarized device light selected from the range of 20-80%, and a transmittance for s-polarized device light selected from the range of 20-80%, for at least one of XC2 and Xci, or (ii) a reflectance for s-polarized device light of at least 90%, and a reflectance for p-polarized device light selected from the range of 20-80% , and a reflectance for p-polarized device light selected from the range of 20-80% for at least one of c2 and Xci. Hence, for the second polarization redirection optics (PPBS2) at least one of s- and p- polarization may both be reflected and transmitted (whereas the other one of s- and p- polarization may essentially be reflected or essentially be transmitted). Further, in embodiments the second polarization redirection optics (PPBS2) may e.g. be fully reflective for s-polarized device light or fully transmissive for p-polarized device light (though other options are herein (thus) not excluded).

[0056] In first approximation, for a specific type of light, transmittance and reflectance at (polarization) redirection optics may add up to 100%. Hence, for phrases like “a reflectance for s-polarized device light selected from the range of 20-80%, and a transmittance for s-polarized device light selected from the range of 20-80%”, and similar phrases, may also apply that a reflectance for s-polarized device light selected from the range of x% wherein x is selected from the range of 20-80, and a transmittance for s-polarized device light selected from the range of (100-x) %, and likewise in similar phrases. In specific embodiments, the light generating devices and the first polarization redirection optics may be rotatable about an axis of the beam of device light comprising one or more of first device light and second device light incident on the second polarization redirection optics. To this end, the system may comprise a rotational element. Therefore, in embodiments the system may comprise a rotational element comprising the first light generating device and the second light generating device, wherein the control system may be configured to control the spectral power distribution of the system light by controlling a rotation of the rotational element relative to the second polarization redirection optics (PPBS2) (and wherein the polarization control system comprises the rotational element). As can be derived from the above, the rotational element may also comprise the first polarization redirection optics. Hence, in specific embodiments, the first light generating device, the second light generating device, and the first polarization redirection optics may not be rotatable relative to each other, but may be together rotatable around the optical axis of the output beam of the rotational sub-assembly comprising the first light generating device, the second light generating device, and the first polarizing beam splitter. The rotational element may be rotated with a movement device, such as a rotary actuator. Hence, the polarization control system may comprise the rotational element (and a movement device for rotating the rotational element).

[0057] For thermal management, a thermally conductive material may be applied, configured in thermal contact with one or more of the first light generating device and the second light generating device. For instance, in embodiments the system, especially the rotation element, may further comprise a device support configured to support the first light generating device and the second light generating device, wherein the device support may be thermally conductive.

[0058] Instead of a movement, such as a rotation, of the light generating devices, (or in addition thereto) the polarization may also be controlled by a movement, such as a rotation, of a polarization rotator. Hence, in embodiments the polarization control system comprises a polarization rotator configured downstream of the first polarizing redirection optics (PBS1) and upstream of the second polarization redirection optics (PPBS2). The polarization rotator may comprise a birefringent rotator, such as a !4 X plate. Hence, in specific embodiments, the polarization rotator may comprise a birefringent rotator, wherein the birefringent rotator comprises a / 2 waveplate; wherein the polarization control system may be configured to control rotation of the birefringent rotator. Hence, the polarization control system may comprise the polarization rotator (and a movement device for rotating the polarization rotator). More especially, the control system may be configured to control rotation of the birefringent rotator.

[0059] As indicated above, the system may further comprise a diffuser system. In embodiments, the diffuser system may comprise a (surface) diffuser. Especially, in embodiments, the diffuser may comprise an element comprising a light-diffusive material, such as e.g. a silica, ground glass, a polymeric material, a ceramic material, a metal(lic) material, a white material, and a rough-surfaced material. Further, in embodiments, the diffuser may comprise a diffractive optical element, such as e.g. a diffractive diffuser, or a holographic optical element, such as e.g. metasurfaces comprising multiple different subwavelength features at the surface of a substrate such as fused silica.

[0060] Further, in embodiments, the diffuser system may comprise a polarization converter. Especially, in embodiments, the polarization converter may comprise a birefringent rotator, more especially a X / 4 waveplate. As known from the art, a waveplate or retarder is an optical device that alters the polarization state of a light wave travelling through it. A halfwave plate may shift the polarization direction of linearly polarized light (especially from s to p or from p to s polarization), and a quarter-wave plate may convert linearly polarized light into elliptically (such as especially circularly) polarized light (and vice versa).

[0061] The polarization converter may especially be configured between the diffuser and the second polarization redirection optics. Hence, the second polarization redirection optics may direct device light to the diffuser via the polarization converter and diffused device light may propagate to the light exit via the polarization converter and the second polarization redirection optics.

[0062] The polarization converter, such as the X / 4 waveplate, may, in embodiments, be configured to convert device light received by the polarization converter comprising a linear polarization into device light having a (first) circular polarization. At the diffuser, in embodiments, the device light having the (first) circular polarization may be diffused into diffused device light having a second circular polarization. Therefore, in embodiments, the polarization converter may also be configured to convert diffused device light received by the polarization converter (via the diffuser) and having the (second) circular polarization into diffused device light comprising a linear polarization. For example, in embodiments, p- polarized device light may be directed by the second polarization redirection optics to the polarization converter. In such embodiments, the polarization converter, such as the X / 4 waveplate, may be configured to convert the p-polarized device light into left-handed circularly polarized device light. Further, in such embodiments, the diffuser may be configured to diffuse the left-handed elliptically (like circularly) polarized device light received by the diffuser into right-handed elliptically (like circularly polarized third diffused device light. Hence, the handedness may change, but the polarization, i.e. elliptically (like circularly), may substantially maintain. The polarization converter may then, in embodiments, be configured to convert the right-handed circularly polarized third diffused device light received by the polarization converter (back) to linearly polarized light, especially to s-polarized diffused device light. However, in embodiments, different polarizations and conversions from the example described here may be possible too, such as e.g. starting from s-polarized device light. Hence, in embodiments, the diffuser system may comprise an arrangement of a polarization converter and a diffuser.

[0063] The diffuser may, in embodiments, be configured to diffuse at least part of the device light received by the diffuser system into diffused device light. Especially, in embodiments, the diffuser may be configured to diffuse at least 30%, like at least 50%, such as at least 60%, like at least 70% of the device light, received by the diffuser system, into diffused device light. Especially, in embodiments, the diffuser may be configured to diffuse at least 80%, more especially at least 90%, including 100% of the device light received by the diffuser system into diffused device light. In embodiments, the diffuser may especially comprise a substantially polarization maintaining diffuser, i.e., the diffuser may be configured to substantially maintain the polarization of the incident light upon diffusion (and in some embodiments reflection)(even though the handedness may (thus) change). Such embodiments may be beneficial as depolarization at the diffuser may be reduced, therewith improving the efficiency of the contribution of the diffuser arrangement to the system light. Therefore, in embodiments, the diffuser may comprise a metal coated surface textured glass substrate mounted on a heat conductive material such as e.g. a metal or a ceramic. In such embodiments, the heat conductive material may be configured to conduct away heat that may be generated in the diffuser due to some absorption of incident device light.

[0064] Furthermore, in embodiments, the diffuser system may comprise a beam profiler. In embodiments, the beam profiler may be configured between the polarization converter and the diffuser. The beam profiler may especially be configured to adapt a light radiance distribution of the diffused device light received by the beam profiler. Therefore, in embodiments, the beam profiler may, e.g., comprise an engineered diffuser, such as a top-hat diffuser or any other tailored intensity profile adjusting diffuser. Such embodiments may be beneficial as the beam profiler may allow for matching the radiance distribution of the diffused device light optimally with the luminescent material light radiance distribution. Hence, in embodiments the diffuser system may comprise an arrangement of a polarization converter and the diffuser. Further, the polarization converter may comprise a / 4 waveplate, and the diffuser may comprise a polarization maintaining diffuser.

[0065] A solution for the thermal management of the luminescent material may be to, in embodiments, apply (or mount) the (luminescent element especially the) luminescent material onto a rotating element, such as e.g. a rotating (phosphor-)wheel (or disk) or a rotating rod (or cylinder). Such embodiments may enable thermal spreading and cooling without the need for e.g. active water cooling, and thereby enabling maximum possible irradiance values. Hence, in embodiments, the luminescent material may be comprised onto a rotating element. Therefore, in embodiments the system may comprise a rotating element, wherein the rotating element comprises a phosphor wheel (or rod) comprising a first track comprising the luminescent material.

[0066] Alternatively or additionally, the luminescent material may be configured in thermal contact with a thermally conductive material. A thermally conductive material may especially have a thermal conductivity of at least about 20 W / (m*K), like at least about 30 W / (m*K), such as at least about 100 W / (m*K), like especially at least about 200 W / (m*K). In yet further specific embodiments, a thermally conductive material may especially have a thermal conductivity of at least about 10 W / (m*K). In embodiments, the thermally conductive material may be comprised by and / or configured in thermal contact with one or more of a heatsink, a heat spreader, and a two-phase cooling device.

[0067] The above indicated diffuser may be a static diffuser. Alternatively, in embodiments, the diffuser may be a dynamic diffuser, such as e.g. a rotating wheel or a rotating rod, with a reflective diffuser track. Furthermore, in such embodiments, the rotating element may (also) comprise an additional track comprising an additional luminescent material (different from the first luminescent material). Such embodiments may be beneficial as the additional luminescent material may add further color point tunability along a line that may be substantially parallel or at least more parallel to the BBL in a targeted range of color temperatures. However, the skilled person will understand that, in such embodiments, further optical requirements may need to apply for the redirection optics. In contrast to a static diffuser, a dynamic diffuser may provide improved thermal behavior and / or may improve elimination of speckle in the white output light, but may add bulk to the engine volume and rotating mass. Hence, in embodiments, the diffuser may (also) be configured onto a rotating element. In some embodiments, the luminescent material and the diffuser may each be configured on a separate rotating element. Alternatively, in embodiments, the luminescent material and the diffuser may be configured on the same rotating element, such as e.g. combined as separate rings on a rotating wheel or a rotating rod. Hence, in embodiments the system may comprise a rotating element, wherein the rotating element may comprise a phosphor wheel (or rod) comprising (i) a first track comprising the luminescent material and optionally (ii) a second track comprising the first diffuser.

[0068] As indicated above, the light generating system comprises a light generating device. A light generating device may especially be configured to generate device light. Especially, the light generating device may comprise a light source. The light source may especially configured to generate light source light. In embodiments, the device light may essentially consist of the device light. In other embodiments, the device light may essentially consist of converted light source light. In yet other embodiments, the device light may comprise (unconverted) light source light and converted light source light. Light source light may be converted with a luminescent material into luminescent material light and / or with an upconverter into upconverted light (see also below). The term “light generating device” may also refer to a plurality of light generating devices which may provide device light having essentially the same spectral power distributions. In specific embodiments, the term “light generating device” may also refer to a plurality of light generating devices which may provide device light having different spectral power distributions.

[0069] The term “light source” may in principle relate to any light source known in the art. In a specific embodiment, the light source comprises a solid state LED light source (such as an LED or laser diode (or “diode laser”)).

[0070] 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 (OLED), 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 an LED or laser diode). In an embodiment, the light source comprises an LED (light emitting diode). The terms “light source” or “solid state light source” may also refer to a superluminescent diode (SLED).

[0071] 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 (such as LEDs or laser diodes (or “diode lasers”)). Hence, the term LED may also refer to a plurality of LEDs. 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 an 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 an LED with on-chip optics. In embodiments, the light source comprises pixelated single LEDs (with or without optics) (offering in embodiments on-chip beam steering).

[0072] The light source may especially be 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, e.g. having band widths as known for lasers.

[0073] The term “light source” may (thus) refer to a light generating element as such, like e.g. a solid state light source, or e.g. to a package of the light generating element, such as a solid state light source, and one or more of a luminescent material comprising element and (other) optics, like a lens, a collimator. A light converter element (“converter element” or “converter”) may comprise a luminescent material comprising element. For instance, a solid state light source as such, like a blue LED, is a light source. A combination of a solid state light source (as light generating element) and a light converter element, such as a blue LED and a light converter element, optically coupled to the solid state light source, may also be a light source (but may also be indicated as light generating device). Hence, a white LED is a light source (but may e.g. also be indicated as (white) light generating device). The term “light source” herein may also refer to a light source comprising a solid state light source, such as an LED or a laser diode or a superluminescent diode. The term “light source” may (thus) in embodiments also refer to a light source that is (also) based on conversion of light, such as a light source in combination with a luminescent converter material. Hence, the term “light source” may also refer to a combination of an LED with a luminescent material configured to convert at least part of the LED radiation, or to a combination of a (diode) laser with a luminescent material configured to convert at least part of the (diode) laser radiation. In embodiments, the term “light source” may also refer to a combination of a light source, like an LED, and an optical filter, which may change the spectral power distribution of the light generated by the light source. Especially, the term “light generating device” may be used to address a light source and further (optical components), like an optical filter and / or a beam shaping element, etc.

[0074] 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.

[0075] The term “solid state light source”, or “solid state material light source”, and similar terms, may especially refer to semiconductor light sources, such as a light emitting diode (LED), a diode laser, or a superluminescent diode.

[0076] 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” or “solid state material laser” may refer to one or more of a semiconductor laser diodes (may also be indicated as “laser diodes” or diode lasers”), such as GaN, InGaN, AlGalnP, AlGaAs, InGaAsP, lead salt, vertical cavity surface emitting laser (VCSEL), quantum cascade laser, hybrid silicon laser, etc. 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 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. Hence, in embodiments lasers in a laser bank (or “laser array bank”) may share the same optics. The laser light source may be 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.

[0077] The laser 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.

[0078] 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).

[0079] The term “solid state material laser”, and similar terms, may refer to a solid state laser like based on a crystalline or glass body doped with ions, like transition metal ions and / or lanthanide ions, to a fiber laser, to a photonic crystal laser, to a semiconductor laser, such as e.g. a vertical cavity surface-emitting laser (VCSEL), etc. The term “solid state light source”, and similar terms, may especially refer to semiconductor light sources, such as a light emitting diode (LED), a laser diode, or a superluminescent diode. Instead of the term “solid state light source” also the term “semiconductor-based light source” may be applied. Hence, the term “semiconductor-based light source” may e.g. refer to one or more of a light emitting diode (LED), a laser diode, and a superluminescent diode. Hence, the light generating device may comprise one or more of a light emitting diode (LED), a laser diode, and a superluminescent diode.

[0080] A light-emitting diode (LED), such as e.g. a single-junction light emitting diode or multi -junction light-emitting diode, is especially a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor may recombine with electron holes, releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) may be determined by the energy required for electrons to cross the band gap of the semiconductor.

[0081] A laser diode (or diode laser) may be a semiconductor device substantially similar to a light-emitting diode in which a diode pumped directly with electrical current can create lasing conditions at the diode's junction. This is known to a person skilled in the art.

[0082] Superluminescent diodes are known in the art. A superluminescent diode may be indicated as a semiconductor device which may be able to emit low-coherence light. Especially, superluminescent diodes may combine the high power and brightness of laser diodes with the low coherence of conventional light-emitting diodes. The low (temporal) coherence of the source has advantages that the speckle is significantly reduced or not visible, and the spectral distribution of emission is much broader compared to laser diodes, which can be better suited for lighting applications. Hence, in embodiments, the solid state light source may comprise a superluminescent diode. For instance, in further specific embodiments, the solid state light source may comprise a GaN-based superluminescent diode, or an InGaN-based superluminescent diode, or an Al GaN-based superluminescent diode.

[0083] Hence, in embodiments the solid state light sources may be selected from the group comprising a light-emitting diode (such as a single-junction light emitting diode or multi -junction light-emitting diode), a laser diode, and a superluminescent diode.

[0084] As indicated above, the system may comprise a luminescent material. The term “luminescent material” especially refers to a material that can convert first radiation, especially one or more of UV radiation and blue radiation, into second radiation. In general, the first radiation and second radiation have different spectral power distributions. Hence, instead of the term “luminescent material”, also the terms “luminescent converter” or “converter” may be applied. In general, the second radiation has a spectral power distribution at larger wavelengths than the first radiation, which is the case in the so-called downconversion. In specific embodiments, however the second radiation has a spectral power distribution with intensity at smaller wavelengths than the first radiation, which is the case in the so-called up-conversion.

[0085] In embodiments, the term “luminescence” may refer to phosphorescence. In embodiments, the term “luminescence” may also refer to fluorescence. Instead of the term “luminescence”, also the term “emission” may be applied. Hence, the terms “first radiation” and “second radiation” may refer to excitation radiation and emission (radiation), respectively. Likewise, the term “luminescent material” may in embodiments refer to phosphorescence and / or fluorescence. The term “luminescent material” may also refer to a plurality of different luminescent materials. Examples of possible luminescent materials are indicated below. Hence, the term “luminescent material” may in specific embodiments also refer to a luminescent material composition. Instead of the term “luminescent material” also the term “phosphor” may be applied. These terms are known to the person skilled in the art.

[0086] In embodiments, luminescent materials are selected from garnets and nitrides, especially doped with trivalent cerium or divalent europium, respectively. The term “nitride” may also refer to oxynitride or nitridosilicate, etc. Alternatively or additionally, the luminescent material(s) may be selected from silicates, especially doped with divalent europium.

[0087] In specific embodiments the luminescent material comprises a luminescent material of the type AsBsOnT'e. wherein A in embodiments comprises one or more of Y, La, Gd, Tb and Lu, especially (at least) one or more of Y, Gd, Tb and Lu, and wherein B in embodiments comprises one or more of Al, Ga, In and Sc. Especially, A may comprise one or more of Y, Gd and Lu, such as especially one or more of Y and Lu. Especially, B may comprise one or more of Al and Ga, more especially at least Al, such as essentially entirely Al. Hence, especially suitable luminescent materials are cerium comprising garnet materials. Embodiments of garnets especially include A3B5O12 garnets, wherein A comprises at least yttrium or lutetium and wherein B comprises at least aluminum. Such garnets may be doped with cerium (Ce), with praseodymium (Pr) or a combination of cerium and praseodymium; especially however with Ce. Especially, B may comprise aluminum (Al); however, in addition to aluminum, B may also partly comprise gallium (Ga) and / or scandium (Sc) and / or indium (In), especially up to about 20% of B, more especially up to about 10 % of B (i.e. the B ions essentially consist of 90 or more mole % of Al and 10 or less mole % of one or more of Ga, Sc and In); B may especially comprise up to about 10% gallium. In another variant, B and O may at least partly be replaced by Si and N. The element A may especially be selected from the group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb) and lutetium (Lu). Further, Gd and / or Tb are especially only present up to an amount of about 20% of A. In a specific embodiment, the garnet luminescent material comprises (Yi-xLux)3BsOi2:Ce, wherein x is equal to or larger than 0 and equal to or smaller than 1. The term “:Ce”, indicates that part of the metal ions (i.e. in the garnets: part of the “A” ions) in the luminescent material is replaced by Ce. For instance, in the case of (Yi-xLux)3AlsOi2:Ce, part ofY and / or Lu is replaced by Ce. This is known to the person skilled in the art. Ce will replace A in general for not more than 10%; in general, the Ce concentration will be in the range of 0.1 to 4%, especially 0.1 to 2% (relative to A). Assuming 1% Ce and 10% Y, the full correct formula could be (Yo.iLuo.89Ceo.oi)3A150i2. Ce in garnets is substantially or only in the trivalent state, as is known to the person skilled in the art.

[0088] In embodiments, the luminescent material may alternatively or additionally comprise one or more of MS:Eu2+and / or I ESisNs Eu2and / or MAISiN.vEu2and / or Ca2AlSi3O2Ns:Eu2+, etc., wherein M comprises one or more of Ba, Sr and Ca, especially in embodiments at least Sr. Hence, in embodiments, the luminescent may comprise one or more materials selected from the group consisting of (Ba,Sr,Ca)S:Eu, (Ba,Sr,Ca)AlSiN3:Eu and (Ba,Sr,Ca)2SisN8:Eu. In these compounds, europium (Eu) is substantially or only divalent, and replaces one or more of the indicated divalent cations. In general, Eu will not be present in amounts larger than 10% of the cation; its presence will especially be in the range of about 0.5 to 10%, more especially in the range of about 0.5 to 5% relative to the cation(s) it replaces. The term “:Eu”, indicates that part of the metal ions is replaced by Eu (in these examples by Eu2+). For instance, assuming 2% Eu in CaAlSiN3:Eu, the correct formula could be (Cao.98Euo.o2)AlSiN3. Divalent europium will in general replace divalent cations, such as the above divalent alkaline earth cations, especially Ca, Sr or Ba. The material (Ba,Sr,Ca)S:Eu can also be indicated as MS:Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound calcium or strontium, or calcium and strontium, more especially calcium. Here, Eu is introduced and replaces at least part of M (i.e. one or more of Ba, Sr, and Ca). Further, the material (Ba,Sr,Ca)2SisN8:Eu can also be indicated as NfcSis Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound Sr and / or Ba. In a further specific embodiment, M consists of Sr and / or Ba (not taking into account the presence of Eu), especially 50 to 100%, more especially 50 to 90% Ba and 50 to 0%, especially 50 to 10% Sr, such as Bai.sSro.sSis Eu (i.e. 75 % Ba; 25% Sr). Here, Eu is introduced and replaces at least part of M, i.e. one or more of Ba, Sr, and Ca). Likewise, the material (Ba,Sr,Ca)AlSiN3:Eu can also be indicated as MAlSiN3:Eu, wherein M is one or more elements selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca); especially, M comprises in this compound calcium or strontium, or calcium and strontium, more especially calcium. Here, Eu is introduced and replaces at least part of M (i.e. one or more of Ba, Sr, and Ca). Eu in the above indicated luminescent materials is substantially or only in the divalent state, as is known to the person skilled in the art.

[0089] In embodiments, the luminescent material may comprise a luminescent material of the type M’xM2-2xAX6 doped with tetravalent manganese, wherein M’ comprises an alkaline earth cation, M comprises an alkaline cation, and x is in the range of 0-1, wherein A comprises a tetravalent cation, for instance comprising one or more of silicon and titanium, wherein X comprises a monovalent anion, at least comprising fluorine.

[0090] A luminescent material of the type M’xM2-2xAX6 doped with tetraval ent manganese is amongst others described in WO2013121355A1, which is herein incorporated by reference. In an embodiment, M’xM2-2xAX6 comprises K2SiFe (indicated herein also as KSiF system). As indicated above, in another embodiment, M’xM2-2xAXe comprises KRbSiFe (herein also indicated as K,Rb system). In specific embodiments, the luminescent material may comprise (K,Rb)2SiF6:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2SiFe:Mn4+. Alternatively or additionally, in embodiments the third luminescent material may comprise K2TiFe:Mn4+. In embodiments, the third luminescent material may comprise K2(Si,Ti)Fe:Mn4+. As can be derived from the above, “Si,Ti” may indicate one or more of Si and Ti.

[0091] As indicated above, the light generating system may comprise optics. The term “optics” may especially refer to (one or more) optical elements. Hence, the terms “optics” and “optical elements” may refer to the same items. The optics may include one or more of (specular or surface textured) mirrors, reflectors, collimators, lenses, prisms, diffusers, phase plates, polarizers, diffractive elements, gratings, dichroics, selectively reflective and / or selectively transmissive optics, arrays of one or more of the afore-mentioned, etc. Alternatively or additionally, the term “optics” may refer to a holographic element or a mixing rod. In embodiments, the optics may include one or more of beam expander optics and zoom lens optics. See further above for examples of optics. In embodiments, the optics may comprise an integrator, like a “Koehler integrator” (or “Kohler integrator”).

[0092] In specific embodiments, the optics may comprise one or more of an integrating (or “homogenizing”) optics, collimating optics, condensing optics, and reflecting optics. For example, the optics may comprise a beam homogenizer configured upstream of the light exit and configured to combine and homogenize the received light and to provide (homogenized white) system light to the light exit.

[0093] As indicated above, the light generating system may comprise a control system. In embodiments, the control system is configured to control one or more of (a) the first light generating device, (b) the second light generating device, (c) the (rotational) orientation of the rotational element, as described herein, and (d) a rotation of the birefringent rotator as described herein, in specific embodiments such that: (i) in a primary first operational mode the system light has a first correlated color temperature (CCT1), and (ii) in a secondary first operational mode the system light has a second correlated color temperature (CCT2); and wherein CCT2-CCT1>25OK, such as CCT2-CCTl>500 K more especially wherein CCT2-CCTl>1000K; and wherein in the first operational mode of the light generating system the system light is white light having a correlated color temperature selected from the range of at least 5000 K, such as selected from the range of 5000-12000 K, more especially selected from the range of 6000-10000 K, and a color rendering index of at least 65. However, the color rendering index may in embodiments also be higher, such as at least 70, or even higher.

[0094] Further, note that in a first operational mode white light may be generated, and that in a plurality of first operational modes white light with different color temperatures may be generated. Further, would also the radiant flux of one or more of the first light generating device and the second light generating device be controllable, then it may also be possible to provide colored light, like essentially blue light, or essentially green and / or yellow light.

[0095] In embodiments, the control system is configured to control the spectral power distribution of the system light in dependence of one or more of an input signal of a user interface, a sensor signal, and a timer. Further, in embodiments the control system is configured to control the spectral power distribution of the system light in dependence of one or more of an input signal of a user interface, a sensor signal, and a timer.

[0096] 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 from 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.

[0097] 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, Thread, WIFI, LiFi, ZigBee, BLE or WiMAX, or another wireless technology.

[0098] The system, or apparatus, or device may execute an action in a “mode” or “operation mode” or “mode of operation” or “operational mode”. The term “operational mode may also be indicated as “controlling mode”. 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”. 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. The terms “operational mode” or "first operational mode”, and similar terms, may also refer to a plurality of (such) operational modes.

[0099] 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, which can only operate in a single operation mode (i.e. “on”, without further tunability).

[0100] 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. The term “white light”, and similar terms, herein, is known to the person skilled in the art. It may especially relate 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 2000-7000 K, such as in the range of 2700 K and 6500 K. In embodiments, e.g. for backlighting purposes, or for other 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.

[0101] In specific embodiments, the correlated color temperature (CCT) may be selected from the range of 6000-12000 K, like selected from the range of 7000-12000 K, like at least 8000 K. Yet further, in embodiments the correlated color temperature (CCT) may be selected from the range of 6000-12000 K, like selected from the range of 7000-12000 K, in combination with a CRI of at least 70.

[0102] 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 190-380 nm, such as 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”, and similar terms, may especially relate to light having a wavelength in the range of about 380-440 nm. In specific embodiments, the violet light may have a centroid wavelength in the 380-440 nm range. The terms “blue light” or “blue emission”, and similar terms, may especially relate to light having a wavelength in the range of about 440-490 nm (including some violet and cyan hues). In specific embodiments, the blue light may have a centroid wavelength in the 440-490 nm range. The terms “green light” or “green emission”, and similar terms, may especially relate to light having a wavelength in the range of about 490-560 nm. In specific embodiments, the green light may have a centroid wavelength in the 490-560 nm range. The terms “yellow light” or “yellow emission”, and similar terms, may especially relate to light having a wavelength in the range of about 560-590 nm. In specific embodiments, the yellow light may have a centroid wavelength in the 560-590 nm range. The terms “orange light” or “orange emission”, and similar terms, may especially relate to light having a wavelength in the range of about 590-620 nm. In specific embodiments, the orange light may have a centroid wavelength in the 590-620 nm range. The terms “red light” or “red emission”, and similar terms, may especially relate to light having a wavelength in the range of about 620-750 nm. In specific embodiments, the red light may have a centroid wavelength in the 620-750 nm range. The terms “cyan light” or “cyan emission”, and similar terms, especially relate to light having a wavelength in the range of about 490-520 nm. In specific embodiments, the cyan light may have a centroid wavelength in the 490-520 nm range. The terms “amber light” or “amber emission”, and similar terms, may especially relate to light having a wavelength in the range of about 585-605 nm, such as about 590-600 nm. In specific embodiments, the amber light may have a centroid wavelength in the 585-605 nm range. The phrase “light having one or more wavelengths in a wavelength range” and similar phrases may especially indicate that the indicated light (or radiation) has a spectral power distribution with at least intensity or intensities at these one or more wavelengths in the indicate wavelength range. For instance, a blue emitting solid state light source will have a spectral power distribution with intensities at one or more wavelengths in the 440-490 nm wavelength range.

[0103] The light generating system 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, automotive lighting, stage lighting, entertainment lighting, etc.. The light generating system (or luminaire) may be part of or may be applied in e.g. optical communication systems or disinfection systems.

[0104] 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. Hence, in an aspect the invention also provides a lighting device selected from the group of a lamp, a luminaire, a projector device, a disinfection device, a photochemical reactor, and an optical wireless communication device, comprising the light generating system as defined herein. The lighting device may comprise a housing or a carrier, configured to house or support, one or more elements of the light generating system.

[0105] Instead of the terms “lighting device” or “lighting system”, and similar terms, also the terms “light generating device” or “light generating system”, (and similar terms), may be applied. A lighting device or a lighting system may be configured to generate device light (or “lighting device light”) or system light (“or lighting system light”). The terms “light” and “radiation” are herein interchangeably used, unless clear from the context that the term “light” only refers to visible light. The terms “light” and “radiation” may thus refer to UV radiation, visible light, and IR radiation. In specific embodiments, especially for lighting applications, the terms “light” and “radiation” refer to visible light. Herein, the term “visible light” especially relates to light having a wavelength selected from the range of 380-780 nm.

[0106] BRIEF DESCRIPTION OF THE DRAWINGS

[0107] 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:

[0108] Figs. 1-5 schematically depict some embodiments of the system;

[0109] Fig. 6 shows the fractions of the blue radiant power P_B and the luminescence radiant power P L in white light radiant power P_W as a function of the CCT (correlated color temperature (K)), for a blue laser with peak wavelength in operation of 457 nm and a luminescent material providing a dichroically filtered output spectrum (cut on / off: 480 nm) at high irradiance, high temperature operation conditions with color coordinates (x,y) = (0.417;0.558); on the x-axis the CCT (in Kelvin) is indicated and on the y-axis the fraction f is indicated; and

[0110] Fig. 7 schematically depict some application embodiments.

[0111] The schematic drawings are not necessarily to scale.

[0112] DETAILED DESCRIPTION OF THE EMBODIMENTS

[0113] Amongst others, a CCT-tunable high brightness and high flux light source is proposed based on a first and a second light generating device, each of these light generating devices comprising one or more of laser diodes (LDs), super luminescent diodes (SLDs), and stacked multijunction light emitting diodes (MJLEDs), both light generating devices emitting in embodiments substantially the same wavelength light while having a different maximum output power. The light of both light generating devices is combined via a first polarizing beam splitter. The polarization direction of this combined light is in embodiments set via a birefringent polarization rotator or via mechanical rotation of both light generating devices including the first PBS relative to a downstream Partially Polarizing Beam Splitter (PPBS). The PPBS splits off a first portion of the light towards a luminescent converter, and splits off a second portion of the light towards a reflective diffuser. The same PPBS in embodiments combines the luminescent light and the reflectively diffused device light into a white light output beam. In embodiments, both the light beams split off towards the luminescent converter and towards the reflective diffuser comprise light from both the first and the second light generating devices. The ratio of the maximum output power of the first and the second light generating devices, as well as the fraction f of p-polarized light that is reflected by the PPBS or the fraction f of s-polarized light that is transmitted by the PPBS may be defined in relation to the requested tunable range in CCT of the white output light, and are chosen such that maximum output power as well as maximum system efficiency are achieved. In embodiments, thanks to the high “partial fraction” f of the PPBS, the efficiency of the blue channel is significantly improved, as this reduces the depolarization losses in the system. In this way essentially 100% of the installed laser power can be used for any of the CCT’s in the selectable CCT range, while two light generating devices emitting at substantially the same wavelength can be used and only a single beam splitter is needed in addition to the PBS that combines the light from the two light generating devices. This may result in an extremely simple, compact, and most efficient laser-phosphor source that is relative insensitive to depolarization effects in the diffused device light channel and capable of generating relative high output powers in a selectable CCT range.

[0114] Amongst others, for a given range of color temperatures that a system should be able to be set to, a limited difference in output power of two laser banks emitting at the same wavelength may be required when combining these two laser beams via an ordinary PBS. Further, using a partially polarizing beam splitter with a relative high fraction f of s- polarized light that is transmitted (in addition to p-polarized light) or a relative high fraction f of p-polarized light that is reflected (in addition to the s-polarized light) significantly may enhance the reflective blue channel efficiency at the beam combining PPBS; the depolarization losses are reduced by a factor (1-1). Yet, especially portions of both laser sources may beneficially be used for both the luminescent conversion and diffuse reflection by changing the polarization of both laser sources at the same time and in the same way by a single (rotational) component. Further, the fraction f of the PPBS as well as the ratio of the maximum output powers of the two laser sources can be optimized for maximum system efficiency and maximum system output power.

[0115] A basic embodiment is presented in Fig. 1, for which a PPBS has been chosen that has a partial transmission and a partial reflection of s-polarized blue light.

[0116] Fig. 1 schematically depicts an embodiment of a light generating system 1000 comprising a first light generating device 110, a second light generating device 120, a luminescent material 200, a control system 300, optics 500, a polarization control system 600, a diffuser system 1710, and a light exit 1090.

[0117] Especially, each of the light generating devices 110,120 may comprise a solid- state light source 10,20 selected from the group of diode lasers, superluminescent diodes, and multi -junction diodes. In embodiments, the first light generating device 110 may be configured to provide first device light 111 having a first centroid wavelength Xci, and wherein the second light generating device 120 may be configured to provide second device light 121 having a second centroid wavelength XC2. In further embodiments, the first centroid wavelength (Xci) and the second centroid wavelength (Xc2) may individually be selected from the wavelength range of 400-490 nm, more especially selected from the wavelength range of] 440-490 nm. Further, in specific embodiments |Xc2-Xci| < 10 nm.

[0118] Especially, in a first operational mode of the light generating system 1000, the first light generating device 110 may be configured to provide first device light 111 with a first radiant flux Pl, and the second light generating device 120 may be configured to provide second device light 121 with a second radiant flux P2, wherein one of the first radiant flux Pl and the second radiant flux P2 is at least 5% larger than the other one of the first radiant flux Pl and the second radiant flux P2.

[0119] Further, the luminescent material 200 may be configured to convert at least part of the first device light 111 and / or at least part of the second device light 121 received by the luminescent material 200 into luminescent material light 20 E Yet, the diffuser system 1710 may comprise a diffuser 710; wherein the diffuser system 1710 may be configured to diffuse at least part of the first device light 111 and / or at least part of the second device light 121 received by the diffuser system 1710 into diffused device light 711. In embodiments, the optics 500 may comprise redirection optics 510; wherein the redirection optics 510 may comprise a first polarization based redirection optics PBS1 and a second polarization based redirection optics PPBS2. Especially, the first polarization based redirection optics PBS1 may be configured to direct first device light 111 and second device light 121 received by the first polarization based redirection optics PBS1 in an optical path to the second polarization based redirection optics PPBS2; wherein the first device light 111 received by the first polarization based redirection optics PBS1 may comprise first linear polarized light, wherein the second device light 121 received by the first polarization based redirection optics PBS1 may comprise second linear polarized light. Especially, the first linear polarized light and the second linear polarized light may have orthogonal (linear) polarizations.

[0120] In embodiments, the polarization control system 600 may be configured to control a polarization of device light 111,121 propagating from the first polarization based redirection optics PBS1 to the second polarization based redirection optics PPBS2. Further, in embodiments the second polarization redirection optics PPBS2 is (i) partly reflective and partly transmissive for s-polarized device light and transmissive for p-polarized light received by the second polarization redirection optics PPBS2, or is (ii) partly reflective and partly transmissive for p-polarized light and reflective for s-polarized light received by the second polarization redirection optics PPBS2. Yet, in embodiments the second polarization redirection optics PPBS2 may be configured to direct device light received by the second polarization redirection optics PPBS2, during the first operational mode, in an optical path to the luminescent material 200 and / or to the diffuser system 1710 in dependence of a polarization of the device light. Yet, in embodiments the second polarization redirection optics PPBS2 is (also) configured to direct luminescent material light 201 and diffused device light 711 received by the second polarization redirection optics PPBS2 in an optical path to the light exit 1090.

[0121] Especially, the light generating system 1000 may be configured to generate system light 1001. Further, the control system 300 may be configured to control a spectral power distribution of the system light 1001 (by controlling the polarization control system 600).

[0122] In Fig. 1, but also in the other figures of embodiments of system 1000, first device light 111 and second device light 121, comprise light having orthogonal polarizations. Especially, the first device light 111 and the second device light 121 are elliptically polarized or linearly polarized, having orthogonal polarizations. Via the first polarization redirection optics PBS1, a beam of light is provided comprising both the first device light 111 and second device light 121 (assuming both the first device 110 and the second device 120 are in operation, which is the case in the first operational mode). The combined device light 111,121 propagates to the second polarization redirection optics PPBS2. Assuming e.g. PPBS2 as being fully reflective for s-polarized device light or fully transmissive for p- polarized device light, and partially transmissive for device light with the complementary (orthogonal) polarization, that may imply that in general device light with a certain linear polarization will be split and directed partially to the diffuser 710 and partially to the luminescent material 200, with a ratio that may depend on the direction of the linear polarization (referenced to PPBS2). In this way, (simultaneously) luminescent material light 201 and diffused device light 711 is generated, that is again received by the second polarization redirection optics PPBS2, which directs this luminescent material light 201 and diffused device light 711 to the light exit 1090. By controlling the (net) polarization of the combined first device light 111 and second device light 121, with the polarization control system 600, reaching the second polarization redirection optics PPBS2, the spectral power distribution of the system light 1001 escaping from the system 1000 can be controlled.

[0123] In embodiments, the control system may be configured to control the system light (see also further below). Especially, in embodiments, the control system may be configured to control a spectral power distribution of the system light. Further, in embodiments, the control system may be configured to control a radiant flux of the system light. Hence, in embodiments, the control system may be configured to control one or more of a correlated color temperature and a radiant flux of the system light. The control system may especially be configured to control said spectral power distribution by e.g. controlling the polarization control system (see also further below). Additionally or alternatively, in embodiments, the control system may be configured to control said spectral power distribution by controlling the light generating devices. Especially, in such embodiments, the control system may be configured to control the polarization of at least the third light generating device. Hence, in such embodiments, the amount of third device light comprising the first linear polarization and third device light comprising the second linear polarization may be controlled by the control system, which may in turn be controlling the light generating devices.

[0124] Further, in embodiments in the first operational mode of the light generating system 1000 the system light is white light 1001 comprising at least part of the luminescent material light 201 and at least part of the diffused device light 711. Yet, in embodiments the system light may have a correlated color temperature of at least 5000 K.

[0125] Furthermore, in embodiments, the optics 500 may comprise one or more of collimation (“or condensing”) optics 560 and integrating (or “homogenizing”) optics 570.

[0126] Referring to Fig. 1, the laser beam that is incident on the PPBS2 and that comprises the light of two laser banks combined via PBS1 may have a net polarization of which the plane can be rotated around the optical axis of the beam by rotation of the platform on which the laser banks and the PBS1 are mounted. The two laser banks may have different output powers. The PPBS2 has partial transmission and partial reflection properties for (in this case) s-polarized device light, and has an additional DBS dielectric coating that reflects the luminescent light.

[0127] In embodiments, the second polarization redirection optics (PPBS2) may have (i) a transmittance for p-polarized device light of at least 90%, and a reflectance for s- polarized device light selected from the range of 20-80% (especially 30-70%)(and a transmittance for s-polarized device light selected from the range of 80-20% (especially 70- 30%)) for at least one of XC2 and Xci, or (ii) a reflectance for s-polarized device light of at least 90%, and a reflectance for p-polarized device light selected from the range of 20-80% (especially 30-70%)(and a transmittance for p-polarized device light selected from the range of 80-20% (especially 70-30%)) for at least one of XC2 and Xci.

[0128] In embodiments, PBS1 may have a s-polarization reflectance of at least 90% and a p-polarization transmittance of at least 90%. Further, in embodiments, PPBS2 may have a p-polarization transmittance of at least 90% and a fraction f of s-polarization that is transmitted is at least 50%. Further, the PPBS2 may have an additional DBS function with at least 90% reflectance for the luminescent material light 211. The optical powers Pl (of the first device light 111) and P2 (of the second device light 121) may have a ratio R=P2 / P1 which may be at maximum 88% (and which may have orthogonal polarizations).

[0129] In embodiments, the first light generating device 110 may comprises a first laser bank comprising a plurality of first lasers 10, and wherein the second light generating device 120 comprises a second laser bank comprising a plurality of second lasers 20. This embodiment may also apply to the other schematically depicted embodiments of system 1000.

[0130] Referring to Fig. 1 (and other embodiments described (and depicted) herein, the diffuser system 1710 may comprises an arrangement of a polarization converter 720 and the diffuser 710. Especially, the polarization converter 720 may comprise a X / 4 waveplate. The diffuser 710 may comprise a polarization maintaining diffuser.

[0131] Further, in embodiments they system 1000 may comprise a rotational element 620 comprising the first light generating device 110 and the second light generating device 120, wherein the control system 300 is configured to control the spectral power distribution of the system light 1001 by controlling a rotation of the rotational element 620 relative to the second polarization redirection optics PPBS2. Hence, the polarization control system 600 may comprises the rotational element 620. Further, the system 1000 may comprise a device support 1100 configured to support the first light generating device 110 and the second light generating device 120, wherein the device support 1100 is thermally conductive. The device support 1100 may be comprised by the (optional) rotational element 620.

[0132] The rotatable platform can in embodiments rotate the combined laser beam over an angle up to about 90° to adjust the CCT. Due to the PPBS2, the efficiency of the blue channel may be maximized.

[0133] For such configuration, the PPBS may show the polarization-dependent transmission and / or reflection for the device light wavelengths, while it is combined with a relatively simple dichroic filter coating that reflects the luminescent light and transmits the device light. Some characteristics of the system 1000 may include: (a) the light generating devices, such as laser banks, may emit at substantially the same wavelength, or within a relative narrow wavelength range (e.g. within a 10 nm range), in the blue part of the spectrum (e.g. 450-460 nm), (b) light generating devices, such as laser banks, may emit light with orthogonal polarization when considered with respect to the PPBS, (c) the output power P2 capability of the second light generating device may be a fraction R of the output power Pl of the first light generating device, i.e., P2 = R * Pl, where R may e.g. be in the range 0.7- 0.9, (d) the transmission factor f of the s-polarized device light by the PPBS may e.g. be in the range of 0.5-0.6. With these settings, the CCT of the laser-phosphor light engine, i.e. system light 1000 can be set in a range of at least 6500-8000 K by rotation of the net polarization plane of the combined device light beam that enters the PPBS. This is conveniently and in a low-cost way realized by e.g. having the laser banks mounted on / to a heat spreading platform that can be rotated around the optical axis of the combined device light beam with a rotation range of up to 90°. In this way, the depolarization losses in the blue channel (either induced by thermal stress in the lenses, by the reflective diffuser or other optical components in the device light beam path) are reduced to a fraction of ca 0.45 of the losses that would have occurred in a system with a full PBS. Here below, embodiments are especially described in relation to laser banks as embodiments of light generating devices. However, embodiments of light generating devices other than laser banks may also be possible.

[0134] Typically, the use of “laser banks”, being relatively dense assemblies of multiple laser diodes on a shared substrate provided with collimating lenses comprising one lens per diode, is convenient to project a beam of high power laser light onto a luminescent converter without the need for using an inverse beam expander. Depending on the output beam characteristics, additional beam shaping optics may be needed, as indicated in the figure. By using two laser banks with different output powers and with orthogonal polarization, a fixed ratio of p / (s+p) and s / (s+p) in the outgoing beam may be realized. By rotating this combined device light beam emitting unit around the optical axis of its outgoing beam, the ratio of p / (s+p) and s / (s+p) of this beam with reference to the downstream PPBS can be varied.

[0135] In the laser-phosphor systems that we consider here, the blue pump laser power may be about two times the requested luminescent optical power. The CCT range of interest may amongst others be about 6500-8000 K. At about 6500 K, the ratio of yellow optical power to blue optical power may be about 2.5, while at 8000 K this may be about 1.9. The blue depolarization losses may amount to about 20% when using a fully polarizing PBS, or less than half of that when using a PPBS as determined in this invention. Therefore, in a first approximation we may use an assumed 10% blue depolarization losses. On the other hand, the collection efficiency of the diffused device light can be significantly higher than that of the luminescent light, as the luminescent material acts as a Lambertian emitter while the diffuse reflector may diffuse the light only over a limited range and therefore result in a much more forward peaked radiance profile. We may assume that the effective collection efficiency for diffused device light in this way may be ca 10% higher than for luminescent light; the latter typically shows an effective collection efficiency of ca 80%. Effective collection efficiency may be used here for the combination of the collection efficiency of light by the condenser lenses and the aperture efficiency of an aperture used to create the requested sharp edge of the white light output beam of the engine. This means that the depolarization losses and the collection efficiency gain of the blue channel relative to the luminescent channel may more or less cancel, and we may end up with a required blue optical pump power that needs to be 4 - 5 x higher than the blue optical power needed for the diffused blue channel for the targeted CCT range. Hence, PBR Ppump / Pbiue may be between about 4-5. The relative contribution of the blue radiant power and of the luminescent radiant power in the white light under typical operating conditions of an entertainment light source as a function of the correlated color temperature CCT of the output white light of the engine is depicted in Fig. 6. In this Figure, a fraction of the blue radiant power P_B and the luminescence radiant power P L in white light radiant power P_W as a function of the CCT is depicted, for a blue laser with peak wavelength in operation of 457 nm and a luminescent material providing a dichroically filtered output spectrum (cut on / off: 480 nm) at high irradiance, high temperature operation conditions with color coordinates (x,y) = (0.417;0.558). From the ratio’s presented in this figure, the PBR value as a function of light engine output CCT is calculated according to the equation

[0136] PBR(CCT) = [BPE / {CEO*TQ*PS*CER}]*[LWR(CCT) / BWR(CCT)], Where

[0137] PBR(CCT) = the Pump to Blue radiant power Ratio as a function of the CCT of the white output light that is required from the blue light generating devices, where the Pump power is going into the conversion channel and the blue power is going into the blue diffusion channel of the engine;

[0138] BPE = Blue Polarization Efficiency (i. e. , 1 - blue light efficiency losses due to depolarization in optical components); CEo = Conversion Efficiency of the luminescent material at reference conditions (low irradiance, low temperature); TQ = Thermal Quenching of the luminescent material at hot operating conditions; PS = Photo Saturation of the luminescent material at high irradiance conditions; CER = Collection Efficiency Ratio of diffused blue light to luminescent light (excluding depolarization phenomena); LWR(CCT) = the Luminescence to White light radiant power Ratio as a function of the CCT;

[0139] BWR(CCT) = the blue light to White light radiant power Ratio as a function of the CCT.

[0140] For the preferred laser wavelength, luminescent material, and operating conditions we have

[0141] CEo ~ 0.69 (for YAG:Ce luminescent converter at room temperature) TQ ~ 0.97 (for YAG:Ce luminescent converter at 150-180 °C)

[0142] PS ~ 0.79 (for ceramic YAG:Ce luminescent converter at 60 W / mm2irradiance)

[0143] BPE ~ 0.9

[0144] CER ~ 1.1 These inputs enable determination of the minimum difference in power from the two laser banks as well as the maximum fraction of s-polarized device light that needs to be transmitted by the PPBS. Using a PPBS that transmits all p-polarized blue light and a fraction f of s-polarized blue light, and assuming that Pl > P2 (as would always be the case for the configurations and CCT ranges of interest) gives us the following set of equations:

[0145] Ppump,max P l + PP2 PBRmax * Pblue,min

[0146] Pblue,min=(l-fJ^PZ

[0147] Ppump,min P2 + f*P l < PBRmin * Pblue,max

[0148] Pblue,max=(l-f)*Pl, where

[0149] Ppump,max is the maximum blue optical pump power available for the luminescent conversion and needed to reach the lowest CCT; Pbiue, min is the minimum blue optical power available for the diffusion channel and needed to reach the lowest CCT; Ppump,min is the minimum blue optical pump power available for the luminescent conversion and needed to reach the highest CCT; Pbiue, max is the maximum blue optical power available for the diffusion channel and needed to reach the highest CCT;

[0150] Pl is the optical power from the first and highest power laser bank; P2 is the optical power from the second and lowest power laser bank; PBRmax = the maximum PpUmp / Pbiue ratio needed to cover the requested CCT range (i. e. , to enable the lowest CCT bound); PBRmin = the minimum PpUmp / Pbiue ratio needed to cover the requested CCT range (i.e. , to enable the highest CCT bound); f = the fraction of s-polarized device light that is transmitted by the PPBS, or, in alternative configurations, the fraction of p-polarized device light that is reflected by the PPBS.

[0151] Unknowns to solve are: P2 / P1 and f From the above equations we can derive the requirements: f > (PBRmax - Pl / P2) / (1 + PBRmax), Or P2 / P1 > l / ( PBRmax - (1+ PBRmax)*f), and f < (PBRmin - P2 / P 1) / (1 + PBRmin) , Or P2 / P1 < PBRmin - (1+ PBRmin)*f

[0152] The system performance is optimized when the fraction f is maximized, as that results in the lowest depolarization losses in the blue channel, and when the laser bank output power ratio is minimized, as that results in maximum system output power. For the ideal case a rotation angle 0 is minimum, i.e., 0 = 0°, for the lowest CCT, while it is maximum, i.e., 0 = 90°, for the highest CCT. Solving this set of equations gives for the ideal configuration the following expressions: fideal—PBRmin / (PBRmin + 1)—l / (PBRmax + 1), and (P2 / Pl)ideal = (PBRmin + 1) / (PBRmax + 1)

[0153] If we relate the PBR ratio’s to the whole range of CCT values possibly of interest, just as in the example mentioned above, the ideal P2 / P1 ratio’s and f-values of the PPBS can be indicated as a function of the variably chosen lower and upper CCT bounds. For a lower CCT bound in the range of 5000 - 8000K and an upper CCT bound in the range of 7000 - 10000 K, this overview of the ideal P2 / P1 ratio’s is presented in Table la, and the overview of the corresponding ideal fractions f is presented in Table lb.

[0154] Table la: ideal ratio of the output powers P2 / P1 (where P2< Pl) of the two laser banks to enable a requested CCT range for the white output light of the laser-phosphor engine, as defined by the selected lower CCT bound and upper CCT bound:

[0155] Referring to above table, it can be seen that the differences in radiant fluxes between the two sources of light allow a broader tunability of the spectral power distribution of the system light (generated by the light generating system) (as will also be further described below). Would the ratio be 1 then only a single CCT value would be possible for the first operational mode, where this CCT value is determined by the fraction f of s- polarized device light that is transmitted by a PPBS that is substantially transmissive for p- polarized device light (as indicated by Table lb) (or, alternatively, by the fraction f of p- polarized device light that is reflected by a PPBS that is substantially reflective for s- polarized device light). However, for values lower than 1, in principle the smaller the P2 / P1 ratio, the larger the CCT range that would be possible, for the first operational mode, to select the system output CCT from with the polarization control system, where the upper and lower bounds of this CCT range are determined by the fraction f of s-polarized device light that is transmitted by a PPBS that is substantially transmissive for p-polarized device light (as indicated by Table lb) (or, alternatively, by the fraction f of p-polarized device light that is reflected by a PPBS that is substantially reflective for s-polarized device light).

[0156] Table lb: Ideal value of the f-factor of the PPBS in the laser-phosphor engine to enable a requested CCT range for the white output light of the engine as defined by the selected lower CCT bound and upper CCT bound, while minimizing the blue channel losses due to depolarization by any optical component in the optical path of the blue channel:

[0157] Obviously, if the lower and upper CCT bounds are equal, then we have a fixed color point system, and for the ideal case the output powers of the laser banks are equal. Note that still a significant factor f is needed and allowed to reach the requested color point (and thus still providing a large blue light polarization loss reduction). For the requested CCT range of 6500 - 8000K, we see that

[0158] (P2 / Pl)ideai = 0.82, and fideal = 0.55.

[0159] In practice, however, there are limited predefined options of commercially available laser banks, and therefore for the power ratio of the two laser banks in the targeted laser-phosphor engine. In case a certain P2 / P1 ratio is chosen that enables a requested CCT range, then the resulting best value for f is found from the equation fbest = (PBRmin - P2 / P1) / (1 + PBRmin)

[0160] In the same way, in case a certain f value would have been chosen (or is available), then the resulting best value for P2 / P1 is found from the equation

[0161] (P2 / Pl)best = PBRmin - (1 + PBRmin) * f

[0162] To still enable the requested CCT range, this means that the ratio P2 / P1 needs to be chosen smaller than, but as close as possible to, the ideal value. With predefined options of commercially available laser banks, this results in a modified overview for this P2 / P1 ratio as presented in Table 2a.

[0163] Table 2a: best choice of the laser bank output power ratio P2 / P1 based on available laser banks while enabling a requested CCT range in the white light output of the laser-phosphor engine, indicated by the lower CCT bound and the upper CCT bound:

[0164] For these practically best P2 / P1 ratio’s, again the corresponding best values for the fraction f can be determined, using the expression for the highest f as a function of P2 / P1 and PBRmin. For this case we need to take into consideration that enabling the highest f values results in the requirement that the rotation angle 0max = 90° for the highest CCT, while the lower bound CCT is reached at an angle 0° < 0min < 90°, and actually lower CCT values than requested are enabled by selecting 0° < 0 < 0min. The resulting overview for the optimal f values in case of practically best P2 / P1 ratio’s from available laser banks is presented in Table 2b.

[0165] Table 2b: best chosen value of the f-factor of the PPBS in the laser- phosphor engine to enable a requested CCT range for the white output light of the engine as defined by the selected lower CCT bound and upper CCT bound, when the best possible laser bank output power ratio P2 / P1 has been chosen for the available laser banks, while minimizing the blue channel losses due to depolarization by any optical component in the optical path of the blue channel:

[0166] From these overviews we see that, for a requested CCT range of 6500 - 8000 K, the optimal choices for P2 / P1 and f are:

[0167] (P2 / Pl)best = 0.71, and fiest = 0.57.

[0168] With these choices the system can actually cover the CCT range from 6000- 8000 K. The luminescent material was chosen to have a luminescence color point that results in a suitable “phosphor load line” connecting the color points of the device light and the luminescent light in the output white light. As a consequence, the ratio of these two contributions may determine the location of the white output light color point on this load line. The luminescent material was chosen to result in a crossing with the BBL at ca 7500 K and have an acceptable color point for all CCT’s in the range of 6500-8000 K. The luminescent equivalence of the radiant output power of the engine is a function of the CCT. With the best choice for the available relative laser bank output powers as a function of the requested lower and upper CCT bounds and the luminous equivalence as a function of the output CCT, the relative luminous flux at the lower and the upper CCT bounds can be determined. This is indicated in Table 3a for the output at the lower bound of a selected CCT range, and in Table 3b for the output at the upper bound of a selected CCT range.

[0169] Table 3a: Relative luminous flux of the output white light at the lower

[0170] CCT bound of a chosen CCT range for the laser-phosphor engine when using the best available laser bank output power ratio and the corresponding best f-factor for the PPBS:

[0171] Table 3b: Relative luminous flux of the output white light at the upper

[0172] CCT bound of a chosen CCT range for the laser-phosphor engine when using the best available laser bank output power ratio and the corresponding best f-factor for the PPBS:

[0173] Obviously, the maximum flux may be achieved at the lowest CCT for both the lower CCT bound and the upper CCT bound. For the targeted range of 6500- 8000 K, we see that the luminous flux at 8000 K is 93% of the output luminous flux at 6500K. For the general overview for all possible CCT ranges, this ratio is indicated in Table 3c.

[0174] Table 3c: Ratio of the luminous flux output of the laser-phosphor engine at the upper CCT bound relative to the flux output at the lower CCT bound of a selected CCT range as defined by the selection of upper and lower CCT bounds in the overview:

[0175] Although the best selectable laser bank ratio and factor f of the PPBS are both a function of the lower and upper CCT bounds, we see that there are quite large ranges for these bounds that enable quite constant performance. As an example, with the best choice for a range of 6500-8000K, the lower bound can be reduced to 6000 K without impact, while the upper bound may be increased to ca 10000 K with only a small impact, as the f-factor reduces then only from 0.57 to 0.51. This means that in this whole range the polarization loss reduction is somewhat over a factor 2. Of course, the luminous flux decreases further with increase of the upper bound, but even at 10000 K the flux only reduces to 88% of the flux at 6500 K. Therefore, with a chosen laser bank combination and value for the f-factor of the PPBS still quite some changes in the target CCT range can be made with a relative limited impact.

[0176] Note that a smaller ratio P2 / P1 may allow for a larger range of CCT settings. Would this be realized by different laser diode counts in the two laser banks, then these laser diodes can all be operated at their nominal current. However, a smaller ratio of P2 / P1 may also imply a smaller maximum output power from the total system, as the maximum power of Pl may be defined by either the available laser banks or the maximum size (system volume or optical components) constraints. As we may strive for maximum output power that can be achieved with only 2 laser banks, a maximum ratio P2 / P1 that still enables the targeted CC range (i. e. , as close as possible to, but not larger than, the ideal value) may be desirable.

[0177] In embodiments, P2 / P1 ratios may be selected such that e.g. a CCT values selected from the range of 5500-8500 K CCT may be achievable. In embodiments, a CCT tuneability over at least 500 K (within this range) may be desirable. In embodiments, an upper CCT bound may be selected from the range of 6000-8500K and a lower CCT bound may be selected from the range of 5500-8000K range. For that, a useful P2 / P1 ratio (see Table la) may be in the range of 0.60 - 0.96. Referring to currently available laser banks (with different number of laser diodes), then it appears that this ratio may change to 0.5 - 0.86 (see Table 2a).

[0178] Hence, with a decreasing ratio P2 / P1, also the maximum total blue laser power and the maximum optical output power of the system may decrease. Therefore, with an increasing requested CCT range that can be covered in the first operational mode, the maximum luminous flux that can be delivered when selecting the lowest CCT of that range and when selecting the highest CCT of that range, may reduce. Because the luminous equivalence may decrease with increasing CCT, also the luminous flux may reduce with increasing CCT. This combined effect is presented in Tables 3a-3b). Table 3c presents the ratio of the luminous flux at the upper bound and the luminous flux at the lower bound of the chosen CCT range. Hence, it shows how much the maximum system output flux would vary when changing the CCT over that complete CCT range. This may apply when keeping all drive currents constant, and only change the CCT of the system output by controlling the polarization of the device light. Of course, by changing the relative drive currents of the first and second light generating devices the CCT of the system output light can be adjusted as well, and over a larger range than what is possible by controlling the polarization of the device light. However, this may come at the cost of a further reduced system output flux.

[0179] Further, the reflective diffuser may in embodiments be a surface diffuser to substantially maintain the polarization of the incident light upon reflection / diffusion. This may be realized by e.g. a metal coated surface textured glass substrate mounted on a heat conductive material such as a metal or a ceramic to conduct away the heat that is generated in the diffuser due to some absorption of incident laser light. The diffuser may be a static diffuser or it may be a dynamic diffuser such as a rotating wheel with a reflective diffuser track.

[0180] The luminescent material (in the reflective mode) may give rise to quite a lot of thermal dissipation. Therefore, this material is preferably applied onto a rotating wheel, enabling superior thermal spreading and cooling without the need for e.g. active water cooling, and thereby enabling maximum possible irradiance values. The most efficient system is achieved by pumping a cerium-doped aluminum garnet phosphor emitting in the yellow-green spectral range with a pump wavelength around 450 nm. A ceramic luminescent converter may be preferred thanks to its superior thermal properties, although e.g. silicon- embedded luminescent particles may be preferred from cost reasons.

[0181] In (first) alternative embodiments, the rotation platform may not be located at the optical beam exit side of the unit comprising at least the laser banks and the beam combiner PBS1, but at the back side opposite to the light emitting side. This is in particular interesting when enabling rotation of the unit relative to not only the downstream optical part of the engine, but also relative to the heat sink that may preferably be mounted at the back side of the unit and that preferably is (quasi-)static in position. Such configuration is even more preferred when mounting both laser banks on a shared heat spreader that in this case is directly thermally connected to the (external) heat sink. This embodiment is schematically depicted in Fig. 2. Fig. 2 schematically depicts an embodiment wherein the rotatable platform is located at the backside of the device light generating unit opposite to the light emitting side. The blue device light emitting laser banks may be mounted on a shared heat spreader that also acts as the thermal interface to an external heat sink. The unit comprising the heat spreader with the laser banks and the beam combiner PBS1 can be mounted to the statically positioned heat spreader under multiple rotation angles around the optical axis of the outgoing combined blue device light beam.

[0182] Like in the embodiment schematically depicted in Fig. 1, PBS1 may have a s- polarization reflectance of at least 90% and a p-polarization transmittance of at least 90%. Further, in embodiments, PPBS2 may have a p-polarization transmittance of at least 90% and a fraction f of s-polarization that is transmitted is at least 50%. Further, the PPBS2 may have an additional DBS function with at least 90% reflectance for the luminescent material light 211. The optical powers Pl (of the first device light 111) and P2 (of the second device light 121) may have a ratio R=P2 / P1 which may be at maximum 88% (and which may have orthogonal polarizations).

[0183] In second alternative embodiments, the luminescent converter and the reflective diffuser may be combined as concentric rings on a rotating wheel or disk or as parallel rings on a rotating cylinder. This may be particularly relevant as the high irradiance of blue device light on a polarization preserving reflective diffuser may lead, even with the low absorption that might be realized with such diffusers, to failure of this component, as in a static diffuser assembly without advanced heat pipe, phase change, or liquid cooling, the thermal management capability may be limited. In that case, even the presence of light absorbing dust or other contamination of the reflector surface might result in a thermal runaway. When applying the diffuser on a rotating wheel or cylinder, the thermal load is spread over a much larger surface area and the thermal risks are therefore significantly reduced. As an example, the embodiment comprising a rotating wheel with concentric rings is schematically depicted in Fig. 3. Fig. 3 schematically depicts an embodiment wherein the unit providing the combined device light beam is mounted rotatably around the optical axis of the outgoing beam on a (statically positioned) heat sink. Here the luminescent material and the diffuser may be applied in a reflective operating mode in the form of concentric rings on a shared rotating wheel.

[0184] Hence, in embodiments the light generating system may comprise a rotating element 1250, wherein the rotating element 1250 comprises a phosphor wheel or phosphor rod comprising (i) a first track comprising the luminescent material 200 and optionally (ii) a second track comprising the first diffuser 710.

[0185] Like in the embodiment schematically depicted in Figs. 1-2, PBS1 may have a s-polarization reflectance of at least 90% and a p-polarization transmittance of at least 90%. Further, in embodiments, PPBS2 may have a p-polarization transmittance of at least 90% and a fraction f of s-polarization that is transmitted is at least 50%. Further, the PPBS2 may have an additional DBS function with at least 90% reflectance for the luminescent material light 211. The optical powers Pl (of the first device light 111) and P2 (of the second device light 121) may have a ratio R=P2 / P1 which may be at maximum 88% (and which may have orthogonal polarizations). This approach may result in a relatively compact system while providing superior thermal management to both the luminescent material and the reflective diffuser. Various mounting methods of the device light generating unit onto the heat sink may be applied, such as clamping, bolting, etc. Preferably a thermal interface material such as a phase change material may be applied in between to ensure proper thermal contact with low thermal resistance.

[0186] In third alternative embodiments the PPBS2 may fully (or at least substantially) be transmissive for p-polarized device light and for the luminescent light, while it may be partly transmissive and partly reflective for s-polarized device light. The fraction of transmitted s-polarized device light to the incident s-polarized device light is referred to by a fraction f, similar to the previous cases in which the PPBS2 reflected a fraction f of incident p-polarized device light (while being fully reflective for s-polarized device light). This configuration is schematically depicted in Fig. 4. Fig. 4 schematically depicts an embodiment wherein the PPBS2 is substantially transmissive for p-polarized device light and for the luminescent light, while it is reflective for only a limited portion of s-polarized device light and transmissive for a (relatively large) portion of s-polarized device light.

[0187] Here, PBS1 may (also) have a s-polarization reflectance of at least 90% and a p-polarization transmittance of at least 90%. However, in embodiments, PPBS2 may have a s-polarization reflectance of at least 90% and a fraction f of p-polarization that is reflected of at least 50%. Further, the PPBS2 may be at least 90% transmissive for the luminescent material light 211. The optical powers Pl (of the first device light 111) and P2 (of the second device light 121) may have a ratio R=P2 / P1 which may be at maximum 88% (and which may have orthogonal polarizations).

[0188] Note that for this configuration the transmittance of the PPBS dielectric coating may need to be designed with intrinsic transmittance for the luminescent spectral range, while in the previous configurations the PPBS dielectric coating could be designed irrespective of its behavior in the luminescent spectral range, as there a simple dichroic filter coating that is reflective for luminescent light and transmissive for device light can conveniently be applied even separate from the PPBS coating.

[0189] In fourth alternative embodiments the rotation of the net polarization direction of the combined device light beam may not be realized by rotation of the combined device light beam generating unit, but by rotation of an additional birefringent rotator that is mounted in between the PBS1 and the PPBS. This may have the advantage of a simplified mechanical mounting of the device light generating unit, but adds an additional precision optical component. An example of such configuration is schematically depicted in Fig. 5. Fig. 5 schematically depicts an embodiment wherein the rotation of the net polarization direction of the combine device light beam may not be realized by mechanical rotation of the combined device light beam generating unit around the optical axis of the beam, but by an additional birefringent rotator such as a half wave plate that is located between the PB1 and the PPBS components and mounted under a requested rotation angle corresponding with the requested CCT of the laser-phosphor white output light.

[0190] Like in the embodiment schematically depicted in Figs. 1-2, PBS1 may have a s-polarization reflectance of at least 90% and a p-polarization transmittance of at least 90%. Further, in embodiments, PPBS2 may have a p-polarization transmittance of at least 90% and a fraction f of s-polarization that is transmitted is at least 50%. Further, the PPBS2 may have an additional DBS function with at least 90% reflectance for the luminescent material light 211. The optical powers Pl (of the first device light 111) and P2 (of the second device light 121) may have a ratio R=P2 / P1 which may be at maximum 88% (and which may have orthogonal polarizations).

[0191] Referring to Fig. 5, in embodiments the polarization control system 600 may comprise a polarization rotator 610, wherein the polarization rotator 610 is configured downstream of the first polarizing redirection optics PBS1 and upstream of the second polarization redirection optics PPBS2. In embodiments, the polarization rotator 610 may comprise a birefringent rotator, wherein the birefringent rotator comprises a k / 2 waveplate. Especially, the polarization control system 600 may be configured to control rotation of the birefringent rotator. The control system 300 may control the polarization control system 600. The latter may e.g. comprise a (rotary) actuator. Hence, the control system 300 may be configured to control rotation of the birefringent rotator.

[0192] Referring to amongst others the embodiments schematically depicted in Figs. 1-5, in embodiments (a) 1.05<P2 / Pl<4 or (b) 0.25<P2 / Pl<0.95 may apply. In specific embodiments, in the first operational mode of the light generating system (1000) the following may apply: (a) 1.1<P2 / PI<2.86 or (b) 0.35< P2 / Pi<0.9. In embodiments, this may be achieved when the first light generating device 110 has a first rated forward current IRFI, wherein the second light generating device 120 has a second rated forward current IRF2, wherein IRF2 / IRFI>1.05 or IRF2 / IRFI<0.95 . However, this may also be achieved when the first light generating device (110) comprises a first laser bank comprising a plurality of first lasers (10), the second light generating device (120) comprises a second laser bank comprising a plurality of second lasers (20), wherein the first laser bank comprises N1 first lasers (10), wherein the second laser bank comprises N2 second lasers (20), wherein N2 / NI>1.05 or N2 / NI<0.95, (and when both light generating devices are operated with the same forward current).

[0193] Hence, when the light generating devices are operated with respective forward currents (IFI and IF2) that have a ratio ( IFI) equal to the ratio in the respective rated forward currents (I_RF2 / IRFI))” This may be under the assumption that both light generating devices have the same laser diode count. In general, an output power ratio P2 / PK1 (or P1 / P2<1) may be desirable. This may be achieved by: (a) two laser banks with identical laser diodes that are operated at the same rated current, but where the laser diode counts differ (for this, the laser diode ratio has the same condition as the power output ratio), or by (b) two laser banks that have the same or a different number of laser diodes, and where the laser diodes in the two laser banks have different rated currents and therefore are operated at different currents; in case the laser diode counts are the same, then the given IRF2 / IRFI condition holds (and is then essentially equivalent to the P2 / P1 condition); in case the laser diode counts are different, the P2 / P1 condition may still hold, but the IRF2 / IRFI condition may not be necessary.

[0194] In further alternative embodiments, any permutation of the principle presented in the five previously described embodiments is used, such as a birefringent rotator and a PPBS with partial reflectance of p-polarized device light and with combined parallel converter and diffuser tracks on a single rotating cylinder.

[0195] In further embodiments the color point adjustable laser-phosphor light engine comprises one optical branch with a first fully luminescent converting material (or material composition) emitting first (composed) luminescent light and with a second branch in which diffuser material is combined with second luminescent material emitting second luminescent light, where the second luminescent emission is spectrally substantially non-overlapping with the first luminescent emission, resulting in color point tunability of the laser-phosphor engine output light along a line that is substantially parallel or at least more parallel to the BBL in a targeted range of color temperatures. For such embodiment, the PPBS component needs to be substantially reflective for the second luminescent light if it is transmissive for the first luminescent light, and vice versa.

[0196] In yet further embodiments according to this invention, as variants of any of the preceding embodiments, one or more of the laser sources may be high frequency and / or amplitude modulated to enable optical wireless communication (OWC). As luminescent materials are generally far slower in their temporal response (i.e., in their decay rate) compared to the lasers, preferably just the blue laser light is used for this OWC. One may, for simplicity, cost reasons, and robustness, specifically select the light generating device that contributes most to the diffused device light in the output white light to be modulated for this.

[0197] Finally, further variations are possible by using transmissive phosphor (wheel) elements and / or transmissive diffusive elements. Such variations have not been further detailed with drawings or descriptions but may be based on the same or similar principles as described above.

[0198] Fig. 7 schematically depicts an embodiment of a luminaire 2 comprising the light generating system 1000 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 light generating system 1000. Fig. 7 also schematically depicts an embodiment of lamp 1 comprising the light generating system 1000. Reference 3 indicates a projector device or projector system, which may be used to project images, such as at a wall, which may also comprise the light generating system 1000. Hence, Fig. 7 schematically depicts embodiments of a lighting device 1200 selected from the group of a lamp 1, a luminaire 2, a projector device 3, a disinfection device, a photochemical reactor, and an optical wireless communication device, comprising the light generating system 1000 as described herein. In embodiments, such lighting device may be a lamp 1, a luminaire 2, a projector device 3, a disinfection device, or an optical wireless communication device. Lighting device light escaping from the lighting device 1200 is indicated with reference 1201. Lighting device light 1201 may essentially consist of system light 1001, and may in specific embodiments thus be system light 1001. Reference 1300 refers to a space, such as a room. Reference 1305 refers to a floor and reference 1310 to a ceiling; reference 1307 refers to a wall.

[0199] 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". 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.

[0200] 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.

[0201] 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.

[0202] 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.

[0203] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

[0204] 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. In yet a further aspect, the invention (thus) provides a software product, which, when running on a computer is capable of bringing about (one or more embodiments ol) the method as described herein.

[0205] 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.

[0206] 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.

Claims

CLAIMS:

1. A light generating system (1000) comprising a first light generating device(110), a second light generating device (120), a luminescent material (200), a control system (300), optics (500), a polarization control system (600), a diffuser system (1710), and a light exit (1090); wherein: each of the light generating devices (110,120) comprise a solid-state light source (10,20) selected from the group of diode lasers, superluminescent diodes, and multijunction diodes; wherein the first light generating device (110) is configured to provide first device light (111) having a first centroid wavelength (Xci), and wherein the second light generating device (120) is configured to provide second device light (121) having a second centroid wavelength (Xc2); in a first operational mode of the light generating system (1000), the first light generating device (110) is configured to provide first device light (111) with a first radiant flux Pl, and the second light generating device (120) is configured to provide second device light (121) with a second radiant flux P2, wherein one of the first radiant flux Pl and the second radiant flux P2 is at least 5% larger than the other one of the first radiant flux Pl and the second radiant flux P2; the luminescent material (200) is configured to convert at least part of the first device light (111) and / or at least part of the second device light (121) received by the luminescent material (200) into luminescent material light (201); the diffuser system (1710) comprises a diffuser (710); wherein the diffuser system (1710) is configured to diffuse at least part of the first device light (111) and / or at least part of the second device light (121) received by the diffuser system (1710) into diffused device light (711); the optics (500) comprise redirection optics (510); wherein the redirection optics (510) comprise a first polarization based redirection optics (PBS1) and a second polarization based redirection optics (PPBS2); the first polarization based redirection optics (PBS1) is configured to direct first device light (111) and second device light (121) received by the first polarization based redirection optics (PBS1) in an optical path to the second polarization based redirectionoptics (PPBS2); wherein the first device light (111) received by the first polarization based redirection optics (PBS1) comprises first linear polarized light, wherein the second device light (121) received by the first polarization based redirection optics (PBS1) comprises second linear polarized light, wherein the first linear polarized light and the second linear polarized light have orthogonal polarizations; the polarization control system (600) is configured to control a polarization of device light (111,121) propagating from the first polarization based redirection optics (PBS1) to the second polarization based redirection optics (PPBS2); the second polarization redirection optics (PPBS2) is (i) partly reflective and partly transmissive for s-polarized device light and transmissive for p-polarized light received by the second polarization redirection optics (PPBS2), or is (ii) partly reflective and partly transmissive for p-polarized light and reflective for s-polarized light received by the second polarization redirection optics (PPBS2); the second polarization redirection optics (PPBS2) is configured to direct device light received by the second polarization redirection optics (PPBS2), during the first operational mode, in an optical path to the luminescent material (200) and the diffuser system (1710) in dependence of a polarization of the device light; the second polarization redirection optics (PPBS2) is configured to direct luminescent material light (201) and diffused device light (711) received by the second polarization redirection optics (PPBS2) in an optical path to the light exit (1090); the light generating system (1000) is configured to generate system light (1001); the control system (300) is configured to control the polarization control system (600) for controlling a spectral power distribution of the system light (1001); in the first operational mode of the light generating system (1000) the system light is white light (1001) comprising at least part of the luminescent material light (201) and at least part of the diffused device light (711) and wherein in the first operational mode of the light generating system the system light has a correlated color temperature selected from the range of 5000-12000 K and a color rendering index of at least 65; and the control system is further configured to control one or more of (a) the first light generating device and (b) the second light generating device such that (i) in a primary first operational mode the system light has a first correlated color temperature (CCT1), and (ii) in a secondary first operational mode the system light has a second correlated color temperature (CCT2); and wherein CCT2-CCTl>250 K.

2. The light generating system (1000) according to claim 1, wherein (a)1.05<P2 / Pl<4 or (b) 0.25<P2 / Pl<0.95 applies.

3. The light generating system (1000) according to any one of the preceding claims, wherein the first light generating device (110) has a first rated forward current IRFI, wherein the second light generating device (120) has a second rated forward current IRF2, wherein IRF2 / IRFI>1.05 or IRF2 / IRFI<0.95.

4. The light generating system (1000) according to any one of the preceding claims, wherein in the first operational mode of the light generating system (1000) the following applies: (a) 1.1<P2 / PI<2.86 or (b) 0.35< P2 / PI<0.9.

5. The light generating system (1000) according to any one of the preceding claims, wherein the first light generating device (110) comprises a first laser bank comprising a plurality of first lasers (10), and wherein the second light generating device (120) comprises a second laser bank comprising a plurality of second lasers (20).

6. The light generating system (1000) according to claim 5, wherein the first laser bank comprises N1 first lasers (10), wherein the second laser bank comprises N2 second lasers (20), wherein N2 / NI>1.05 or N2 / NI<0.95.

7. The light generating system (1000) according to any one of the preceding claims, wherein the second polarization redirection optics (PPBS2) has (i) a transmittance for p-polarized device light of at least 90%, and a reflectance for s-polarized device light selected from the range of 20-80%, and a transmittance for s-polarized device light selected from the range of 20-80%, for at least one of XC2 and Xci, or (ii) a reflectance for s-polarized device light of at least 90%, and a reflectance for p-polarized device light selected from the range of 20-80% , and a reflectance for p-polarized device light selected from the range of 20-80% for at least one of XC2 and Xci.

8. The light generating system (1000) according to claim 7, comprising a rotational element (620) comprising the first light generating device (110) and the second light generating device (120), wherein the control system (300) is configured to control thespectral power distribution of the system light (1001) by controlling a rotation of the rotational element (620) relative to the second polarization redirection optics (PPBS2).

9. The light generating system (1000) according to claim 8, further comprising a device support (1100) configured to support the first light generating device (110) and the second light generating device (120), wherein the device support (1100) is thermally conductive.

10. The light generating system (1000) according to any one of the preceding claims, wherein the polarization control system (600) comprises a polarization rotator (610) configured downstream of the first polarizing redirection optics (PBS1) and upstream of the second polarization redirection optics (PPBS2).

11. The light generating system (1000) according to claim 10, wherein the polarization rotator (610) comprises a birefringent rotator, wherein the birefringent rotator comprises a X / 2 waveplate; wherein the polarization control system (600) is configured to control rotation of the birefringent rotator.

12. The light generating system (1000) according to any one of the preceding claims, wherein the first centroid wavelength (Xci) and the second centroid wavelength ( c2) are individually selected from the wavelength range of 440-490 nm; and wherein |Xc2-Xci| < 10 nm.

13. The light generating system (1000) according to any one of the preceding claims, wherein the diffuser system (1710) comprises an arrangement of a polarization converter (720) and the diffuser (710); wherein the polarization converter (720) comprises a / 4 waveplate, and wherein the diffuser (710) comprises a polarization maintaining diffuser.

14. The light generating system (1000) according to any one of the preceding claims, wherein the control system (300) is further configured to control one or more of (c) the orientation of the rotational element (620), as defined in claim 8, and (d) a rotation of the birefringent rotator as defined in any one of claims 10-11, such that: (i) in a primary first operational mode the system light (1001) has a first correlated color temperature (CCT1), and (ii) in a secondary first operational mode the system light (1001) has a second correlatedcolor temperature (CCT2); and CCT2-CCT1> 500 K;; and wherein the light generating system (1000) comprising a rotating element (1250), wherein the rotating element (1250) comprises a phosphor wheel comprising (i) a first track comprising the luminescent material (200) and optionally (ii) a second track comprising the first diffuser (710).

15. A lighting device (1200) selected from the group of a lamp (1), a luminaire(2), a projector device (3), and an automotive lighting device, comprising the light generating system (1000) according to any one of the preceding claims.

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