IPC分类号：
F21K9/69 | F21K9/68 | F21K9/64 | H05B47/155 | F21Y103/00 | F21Y115/10
国民经济行业分类号：
C3545 | C3871 | C3976
当前申请(专利权)人：
LUMENCOR, INC.
原始申请(专利权)人：
SIGNIFY HOLDING B.V.
当前申请(专利权)人地址：
14940 NW GREENBRIER PKWY, 97006, BEAVERTON, OREGON
发明人：
HAENEN, LUDOVICUS JOHANNES LAMBERTUS | HOELEN, CHRISTOPH GERARD AUGUST | DE BOER, DIRK KORNELIS GERHARDUS | KADIJK, SIMON EME | LI, YUN
代理人：
PIOTROWSKI, DANIEL J.
摘要：
The invention provides a lighting device (1) comprising a luminescent element (5) comprising an elongated light transmissive body (100), the elongated light transmissive body (100) comprising a side face (140), wherein the elongated light transmissive body (100) comprises a luminescent material (120) configured to convert at least part of a light source light (11) selected from one or more of the UV, visible light, and IR received by the elongated light transmissive body (100) into luminescent material radiation (8). The invention further provides such luminescent element per se.
技术问题语段：
The technical problem described in this patent text is to provide a light emitting device that can convert the light emitted from an LED into light with a different wavelength range, and to achieve a desired emission pattern.
技术功效语段：
The present invention allows for the efficient generation of blue light by using a yellow light with outer and inner rods that make contact with the edge faces of the rods only minimizing light loss. The lighting device also includes holding elements that make contact with the edge faces over less than 10% of the total area to further reduce light loss. Additionally, the lighting device may include a heat sink and/or cooling element with the holding elements. These technical effects improve the performance and efficiency of the lighting device.
权利要求：
1. A lighting device comprising:
a light source configured to provide light source light selected from one or more of ultraviolet (UV), visible light, and infrared (IR);
a luminescent element comprising an elongated light transmissive body, the elongated light transmissive body comprising a side face, wherein:
the elongated light transmissive body comprises a luminescent material,
the elongated light transmissive body has a length (L);
the elongated light transmissive body is hollow over at least part of the length (L) thereby defining a cavity,
the elongated light transmissive body comprises a radiation input face and a first radiation exit window; wherein the luminescent material is configured to convert at least part of light source light received at the radiation input face into luminescent material radiation, and the luminescent element being configured to couple at least part of the luminescent material radiation out at the first radiation exit window as converter radiation,
the elongated light transmissive body has a first face and a second face defining the length (L) of the elongated light transmissive body; wherein the side face comprises the radiation input face, and wherein:
the second face comprises the radiation exit window.
2. The lighting device according to claim 1, wherein the elongated light transmissive body has a polygonal cross-section, and wherein the elongated light transmissive body comprises a cavity surrounded by the elongated light transmissive body.
3. The lighting device according to claim 1, wherein the elongated light transmissive body has a tubular shape having a cavity surrounded by the elongated light transmissive body.
4. The lighting device according to claim 1, wherein at least part of the cavity comprises a light transmissive material, differing in composition from the composition of the material of the elongated light transmissive body, wherein the light transmissive material in the cavity has an index of refraction equal to or lower than the light transmissive material of the light transmissive body.
5. The lighting device according to claim 1, wherein one or more of the first face and the second face comprise a plane comprising surface modulations thereby creating different modulation angles relative to the respective plane.
6. The lighting device according to claim 1, further comprising an optical element optically coupled to the elongated light transmissive body, wherein the elongated light transmissive body and the optical element are a single body.
7. The lighting device according to claim 1, further comprising an optical element optically coupled to the elongated light transmissive body, wherein the optical element is selected from the group consisting of a compound parabolic concentrator, an adapted compound parabolic concentrator, a dome, a wedge-shaped structure, and a conical structure.
8. The lighting device according to claim 1, further comprising an optical element optically coupled to the elongated light transmissive body, wherein the optical element comprises a plurality of optical fibers, optically coupled to the elongated light transmissive body.
9. The lighting device according to claim 1, comprising a plurality of elongated light transmissive bodies, each elongated light transmissive body comprising a luminescent material configured to convert at least part of a light source light selected from one or more of the UV, visible light, and IR received by the elongated light transmissive body into luminescent material radiation, wherein:
the elongated light transmissive bodies differ in one or more of (a) length (L) of the elongated light transmissive bodies, (b) type of luminescent material, (c) concentration of luminescent material, (d) concentration distribution over the elongated light transmissive body, and (e) host matrix for the luminescent material;
each elongated light transmissive body has an axis of elongation (BA);
one or more of the elongated light transmissive bodies comprise cavities;
wherein the elongated light transmissive bodies are configured in a core-shell configuration wherein a smaller elongated light transmissive body is at least partly configured in the cavity of a larger elongated light transmissive body and wherein the axes of elongations (BA) are configured parallel.
10. The lighting device according to claim 9, wherein the elongated light transmissive bodies have side faces, and wherein side faces of adjacent elongated light transmissive bodies have no physical contact or only over at maximum 10% of their respective surface areas.
11. The lighting device according to claim 9, further comprising an optical element, wherein the optical element comprises a first wall and a second wall surrounding the first wall thereby defining an optical element having a ring-like cross-section, wherein the optical element comprises a radiation entrance window and a radiation exit window, wherein the radiation entrance window is optically coupled with the plurality of elongated light transmissive bodies.
12. The lighting device according to claim 1, wherein the first face is facetted or has one or more oblique sides with respect to the side face.
13. The lighting device according to claim 12, further comprising a reflective surface facing the first face and not being in direct contact with the first face of the elongated light transmissive body.
14. The lighting device according to claim 1, further comprising a plurality of light sources, wherein (i) one or more light sources are configured to provide light source light to the side face of an outer elongated light transmissive body and/or wherein one or more light sources are configured to provide light source light to one or more first faces, wherein the one or more first faces are end faces, and/or (ii) wherein one or more light sources are configured in a cavity of an inner elongated light transmissive body and configured to provide light source light to the side face of the inner elongated light transmissive body, wherein at least two elongated light transmissive bodies provide luminescent material light with different spectral distributions, and wherein optionally the lighting device comprises a control system, configured to control the spectral distribution of the lighting device light.
15. A lighting system, comprising:
one or more lighting devices according to claim 1 and,
a controller for controlling the one or more lighting devices.
技术领域：
[0002]The invention relates to a lighting device, such as for use in a projector or for use in stage lighting, comprising an elongated light transmissive body. The invention also relates to a lighting system such as a projection system or luminaire.
BACKGROUND OF THE INVENTION
[0003]Luminescent rods are known in the art. WO2006/054203, for instance, describes a light emitting device comprising at least one LED which emits light in the wavelength range of >220 nm to <550 nm and at least one conversion structure placed towards the at least one LED without optical contact, which converts at least partly the light from the at least one LED to light in the wavelength range of >300 nm to ≤1000 nm, characterized in that the at least one conversion structure has a refractive index n of >1.5 and <3 and the ratio A:E is >2:1 and <50000:1, where A and E are defined as follows: the at least one conversion structure comprises at least one entrance surface, where light emitted by the at least one LED can enter the conversion structure and at least one exit surface, where light can exit the at least one conversion structure, each of the at least one entrance surfaces having an entrance surface area, the entrance surface area(s) being numbered A1 . . . An and each of the at least one exit surface(s) having an exit surface area, the exit surface area(s) being numbered E1 . . . En and the sum of each of the at least one entrance surface(s) area(s) A being A=A1+A2 . . . +An and the sum of each of the at least one exit surface(s) area(s) E being E=E1+E2 . . . +En.
[0004]US2010/124243 A1 discloses a semiconductor light emitting apparatus that includes an elongated hollow wavelength conversion tube having wavelength conversion material dispersed therein. A semiconductor light emitting device is oriented to emit light inside the elongated hollow wavelength conversion tube to impinge upon the elongated wavelength conversion tube wall.
[0005]US2014/185269 A1 discloses a photoluminescent wavelength conversion component and a lamp that incorporates such a component. The photoluminescence wavelength conversion component comprises a hollow cylindrical tube having a given bore of diameter and an axial length. The relative dimensions and shape of the component can affect the radial emission pattern of the component and are configured to give a required emission pattern (typically omnidirectional). The photoluminescence material can be homogeneously distributed throughout the volume of the component during manufacture of the component.
[0006]US2010/053970 A1 discloses a light-emitting device that includes a first laser light source, a first diffusion member provided along a light axis of a first light radiated form the first laser light source, and a first wavelength converter provided along the first diffusion member. The first diffusion member generates a second light from the first light. The second light outgoes in a direction different from the light axis direction of the first light. A ratio of generating the second light from the first light in a first part is higher than that in a second part, wherein an intensity of the first light in the first part is lower than that in a second part. The first wavelength converter absorbs the second light and emitting a third light having a different wavelength from the second light.
[0007]US2007/280622 A1 discloses a light guide that includes a material that is capable of emitting light of a second wavelength when illuminated with light of a first wavelength where the first wavelength is different from the second wavelength. The light guide further includes an exit face that has a first portion that is reflective at the second wavelength and a second portion that is transmissive at the second wavelength. When the light guide is illuminated with light of the first wavelength, the material converts at least a portion of the light of the first wavelength into light of the second wavelength. The majority of the light of the second wavelength that exits the second portion of the exit face is totally internally reflected by the light guide.
发明内容：
[0008]High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection, etc. For this purpose, it is possible to make use of so-called light concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. A rod of such a transparent luminescent material can be illuminated by LEDs and/or laser diodes (LDs) to produce longer wavelengths within the rod. Converted light which will stay in the luminescent material, such as a (trivalent cerium) doped garnet, in the waveguide mode and can then be extracted from one of the (smaller) surfaces leading to an intensity gain.
[0009]In embodiments, the light concentrator may comprise a rectangular bar (rod) of a phosphor doped, high refractive index garnet, capable to convert blue light into green light and to collect this green light in a small étendue output beam. The rectangular bar may have six surfaces, four large surfaces over the length of the bar forming the four side walls, and two smaller surfaces at the end of the bar, with one of these smaller surfaces forming the “nose” where the desired light is extracted (e.g. with an optical element).
[0010]Under e.g. blue light radiation, the blue light excites the phosphor, after the phosphor start to emit green light in all directions, assuming some cerium comprising garnet applications. Since the phosphor is embedded in—in general—a high refractive index bar, a main part of the converted (green) light is trapped into the high refractive index bar and wave guided to the nose of the bar where the (green) light may leave the bar. The amount of (green) light generated is proportional to the amount of blue light pumped into the bar. The longer the bar, the more blue LED's (light emitting diodes) and/or laser diodes can be applied to pump phosphor material in the bar and the number of blue LED's and/or laser diodes to increase the brightness of the (green) light leaving at the nose of the bar can be used. The phosphor converted light, however, can be split into two parts.
[0011]A first part consists of first types of light rays that will hit the side walls of the bar under angles larger than the critical angle of reflection. These first light rays are trapped in the high refractive index bar and will traverse to the nose of the bar where it may leave as desired light of the system.
[0012]Hence, it is an aspect of the invention to provide an alternative lighting device comprising a luminescent concentrator, which preferably further at least partly obviates one or more of above-described drawbacks and/or which may have a relatively higher efficiency. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
[0013]Therefore, in an aspect the invention provides a lighting device having a luminescent element comprising an elongated light transmissive body, the elongated light transmissive body comprising a side face, wherein: (i) the elongated light transmissive body comprises a luminescent material configured to convert at least part of a light source light selected from one or more of the UV, visible light, and IR received by the elongated light transmissive body into luminescent material radiation; (ii) the elongated light transmissive body has a length (L); and (iii) the elongated light transmissive body is hollow over at least part of the length (L) thereby defining a cavity.
[0014]It appears that hollow elongated bodies may have higher efficient outcoupling than massive elongated bodies. Especially, this may apply for elongated bodies have an essentially circular cross-section, though for non-circular cross-sections this may also apply.
[0015]Hence, in embodiments the elongated light transmissive body has a polygonal cross-section, wherein the elongated light transmissive body comprises a cavity surrounded by the elongated light transmissive body. Or, in other words, the material of the elongated light transmissive body is configured such that there is a cavity with the material of the elongated body at least partially surrounding the cavity.
[0016]In yet other embodiments, the elongated light transmissive body is tubular shaped. Therefore, in embodiments the elongated light transmissive body has a tubular shape having a cavity surrounded by the elongated light transmissive body.
[0017]Especially, the cavity has a cross-section having the same symmetry as the cross-section of the elongated light transmissive body. Hence, a tubular shaped elongated body having a circular cross-section may also have a cavity having a circular cross-section. Likewise, an elongated body having a polygonal cross-section may have a cavity also having a polygonal cross-section. Note that it is not necessarily the case that the cavity has a cross-section having the same symmetry as the cross-section of the elongated light transmissive body. Further, the edge(s) of the cavity may be configured essentially parallel to the edge(s) of the elongated light transmissive body. However, when the elongated light transmissive body tapers, in embodiments the edges of the cavity and the elongated body may not be necessarily parallel (see below). Further, the cavity may have the same length as the elongated body or may have a shorter length. In general, at least at one end face (herein in embodiments also indicated as first face and second face) the elongated body may have an opening to the cavity (like a vase).
[0018]Further improvements of the outcoupling may be achieved when the cavity comprises a light transmissive material. Therefore, in embodiments at least part of the cavity, especially the entire cavity, comprises a light transmissive material, differing in composition from the composition of the material of the elongated light transmissive body. In specific embodiments, the light transmissive material in the cavity has an index of refraction equal to or lower than the light transmissive material of the light transmissive body. An example of a suitable filling may comprise one or more of MgF2 or CaF2, silicone, glass or transparent ceramics like spinel, poly-crystalline alumina, sapphire, YAG, a material similar (e.g. when the light transmissive body comprises a garnet, the filling may also comprise a garnet, but based one or more other constituents), or identical (e.g. same garnet material) to the first body material, but especially without the phosphor. The materials should especially be transparent, but could be amorphous, poly-crystalline or single crystalline.
[0019]The drawback of current HLD is that one cannot make use of leakage of blue to make white light. However with the present invention it is possible by making for example yellow light (green+blue) with outer rod and with inner rod one could generate blue. Especially, with no or nearly optical contact of the rods, the efficiency may be higher.
[0020]Blue light can be either added by putting high power blue LED/Laser in front of light guide which is put in the yellow rod. Or one could use a blue HLD rod in the center with 405 nm pumping LED. At the end of the rods, if needed, mixing of light can be done. For theatre and stage lighting an etendue of 16 mm2 sr such as commonly required for beamers is not necessary. An etendue of 500 mm2 sr may be sufficient; may be obtained with bodies with a relatively large cross-sectional area. A larger etendue allows more (low-power) light sources to pump the body. Further, it appears that cylindrical rods can be produced easier and thus also more reliable.
[0021]By putting various diameter cylindrical rods in each other one can generate white light without the use of expensive dichroic mirrors. Even tuning of the spectrum is possible. Also it can be done in an efficient and cost effective way because the making of round rods is in principle cheaper to make. Outside can be easily polished but inside it may be more difficult for small and long rods. Still it seems that scattering of inside rod has less negative effect as scattering at outside rod.
[0022]For facilitating incoupling of light, the tube diameter can be made a bit larger and afterwards taper a bit towards the nose. First simulations show that tapering from a relative diameter 1.00 to towards a relative diameter of 0.60 is possible without essentially losing light (i.e. the diameter reduces towards the nose with 40%). Even, it may be beneficial extracting a bit more light towards the desired direction.
[0023]Use of round shapes may imply an essentially round light distribution which is advantage for lighting applications. Rectangular hollow tubes can also be put together. To mix the colored light from the different round tubes one could use an integrator element, such as especially an integrator rod. For example, one may use FlyEye optics. Optionally, the integrator element is comprised by (i.e. especially integrated in) the elongated light transmissive body. One could also attach this round combination first to a small piece of transparent (rectangular or differently shaped polygonal) tube in order to mix the light properly and then attach the collimator, such as a CPC, or other optical element, such as a dome shaped optical element.
[0024]Hence, the luminescent element may further comprise an optical element optically coupled to the elongated light transmissive body such as a CPC. However, in yet other embodiments the optical element comprises a plurality (i.e. 2 or more) of optical fibers, optically coupled to the elongated light transmissive body. In yet further embodiments, the output side of the optical fibers may be coupled to yet another optical element, such as a collimator, such as a CPC, or other optical element, such as a dome shaped optical element.
[0025]Hence, the luminescent element may comprise a plurality of elongated light transmissive bodies. In embodiments, a single light transmissive body together with the light source may provide white light. However, as indicated above, in general a single light transmissive body and one or more (radiationally coupled) light sources may especially be configured to provide colored light. Hence, when a plurality of elongated light transmissive bodies is applied, this may e.g. be used for providing white light (in a first mode of the lighting device; see further below). Therefore, also single-color systems, multi-color systems, off-BBL or non-white color point, emitting luminescent elements may be provided.
[0026]Especially, as indicated above, when hollow elongated light transmissive bodies are applied, a smaller body may be configured in a cavity of a larger body. Therefore, in specific embodiments, the invention also provides a luminescent element according to any one of the preceding claims, comprising a plurality of elongated light transmissive bodies, each elongated light transmissive body comprising a luminescent material configured to convert at least part of a light source light selected from one or more of the UV, visible light, and IR received by the elongated light transmissive body into luminescent material radiation, wherein: (i) the elongated light transmissive bodies may differ in e.g. one or more of (a) length (L) of the elongated light transmissive bodies, (b) type of luminescent material, (c) concentration of luminescent material, (d) concentration distribution over the elongated light transmissive body, and (e) host matrix for the luminescent material; (ii) each elongated light transmissive body has an axis of elongation (BA); (iii) one or more of the elongated light transmissive bodies comprise cavities; and wherein the elongated light transmissive bodies are configured in a core-shell configuration wherein a smaller elongated light transmissive body is at least partly configured in the cavity of a larger elongated light transmissive body and wherein the axes of elongations (BA) are configured parallel. Alternatively or additionally, the elongated light transmissive bodies may in embodiments also differ in one or more diameter and wall thickness.
[0027]The lengths of the elongated light transmissive bodies may essentially be the same, or may differ.
[0028]In specific embodiments, the elongated light transmissive bodies have side faces, and wherein side faces of adjacent elongated light transmissive bodies have no physical contact or only over at maximum 10% of their respective surface areas.
[0029]In specific embodiments, the elongated light transmissive body has a first face and a second face defining a length (L) of the elongated light transmissive body; wherein the side face comprises the radiation input face, wherein the second face comprises the radiation exit window.
[0030]As indicated herein, the luminescent element may comprise a plurality of light transmissive bodies. Therefore, in yet a further embodiment the invention provides a lighting device as defined herein, comprising the luminescent element with a plurality of elongated light transmissive elements, which are especially configured in a core-shell configuration, wherein the lighting device further comprising a plurality of light sources, wherein one or more light sources are configured to provide light source light to the side face of an outer elongated light transmissive body and/or wherein one or more light sources are configured to provide light source light to one or more first faces, wherein the one or more first faces are end faces, and/or wherein one or more light sources are configured in a cavity of an inner elongated light transmissive body and configured to provide light source light to the side face of the inner elongated light transmissive body. Hence, in embodiments one or more light source may be configured to provide light to an outer side face of an outer (shell) elongated light transmissive body. Alternatively or additionally, in embodiments one or more light source may be configured to provide light to an inner side face of an inner (shell) elongated light transmissive body.
[0031]In embodiments, the multiple elongated bodies may be comprised by a monolithic body where the elongated bodies may not be physically separate, but e.g. only have a different host matrix realized by e.g. 2-component extrusion or 2-component injection molding; see also elsewhere.
[0032]Especially, in a first mode of operation the lighting device is configured to provide white light. However, the lighting device may also be configured to provide (in embodiments another mode of operation) to provide colored light or infrared light. Especially when two or more elongated bodies are applied, in embodiments the spectral distribution of the lighting device light (i.e. the light emanating from the lighting device) may be controllable.
[0033]Hence, in embodiments at least two elongated light transmissive bodies provide luminescent material light with different spectral distributions. This may be used to provide e.g. colored light with e.g. a broad spectral distribution. Especially, the lighting device may further comprise a control system, configured to control the spectral distribution of the lighting device light. The phrase “with different spectral distributions” may in embodiments refer to spectral distributions having intensity averaged emission maxima at wavelengths that are position at least 10 nm, such as at least 20 nm from each other.
[0034]A luminescent element with a plurality of elongated light transmissive bodies may comprise a plurality of optical elements. These may be configured downstream of the radiation exit faces. However, also an integrated optical element may be used, that is configured downstream of more than one of the light transmissive bodies. This may be useful for a core-shell configuration, but also for a configuration wherein a plurality of elongated light transmissive bodies are configured in a bundle kind of configuration.
[0035]Therefore, in embodiments the lighting device may further comprise an optical element, wherein the optical element comprises a first wall and a second wall surrounding the first wall thereby defining an optical element having a ring-like cross-section, wherein the optical element comprises a radiation entrance window and a radiation exit window, wherein the radiation entrance window is optically coupled with the plurality of elongated light transmissive bodies. Such optical element may have a shape like a fluted tube or Bundt pan. However, other options may also be possible (see below), wherein e.g. a tapering in a direction away of the light transmissive body may be possible.
[0036]Light concentrators (herein also indicated as “elongated light transmissive body”, “transmissive body”, “luminescent concentrator”, “luminescent body”, or as “rod”) that may be used in e.g. HLD (high lumen density) light sources may have a rectangular cross section, and (blue LED and/or laser diodes) light from external can coupled-in in the rod and converted by a phosphor to light of longer wavelength. The emission of light by the phosphor is omnidirectional in a random way. That means that a part of the light leaves the rod immediately, by transmission through one of the four long sides of the rod. This light, as a fraction of the total emitted light, is given by the solid angle of the four light cones in which the light has an angle with the rod surface smaller than the critical TIR angle, as compared to the total solid angle of 4π.
[0037]For light concentrators based on YAG or analogous garnet material (see below) the refractive index is close to 1.84, and the solid angle of the 4 cones together occupies 32% (disregarding reabsorption) of the whole space. Assuming no reabsorption, this light can (to a large part) be considered as lost light, as even reflectors around the rod cannot help to get light into total internal reflection (TIR) in the rod. It is important to note that the position of the light generation in the rod has no implication for the relative light fractions.
[0038]Light concentrators can especially be used in combination with optical element for improving outcoupling of the light from the concentrator and/or for beam shaping. A choice for such optical element is an optical concentrator element, such as a compound parabolic concentrator (CPC) (see also below).
[0039]When using a high-index CPCs (n_CPC>1.55 in case of n_rod=1.84), some of the light that is generated very close to the CPC could either be non-TIR or could be coupled out via the CPC, dependent on the exact position.
[0040]Hence, for a light concentrator with a n=1.52 CPC, three light fractions can be discerned, namely Non-TIR light in the cones that are directly transmitted through one of the four long sides.
[0041]Light in the cones that are aligned with the long axis (z-axis) of the rod, this light sometimes is called TIR-to-Nose light, as this light is in TIR in the rod until it hits the CPC, and is transmitted through the CPC. The rays that go into the CPC have an angle with the z-axis that is smaller than the critical TIR angle that holds for the n_rod-n_CPC combination. The light in the cone that is directed towards the tail may at least partly reflect at the tail via TIR or via Fresnel, or via an external mirror (see also below), and also leaves the rod at the CPC.
[0042]The remaining light fraction is in TIR and—in theory, in a perfect rod—these rays cannot escape from the rod. This fraction is sometimes called locked-in TIR light (after the Locked-in syndrome).
[0043]In case n_CPC=n_rod, this locked-in light fraction III does not exist, all the light that is in TIR is leaving the rod via the CPC.
[0044]In case n_CPC<n_rod, there is locked-in light, but in practice the light is not contained in the rod forever, but is scattered after some length, or re-absorbed and re-emitted again, and if this happens in a random way, eventually the light is redistributed over the fractions I and II. Under full randomization of the light by scattering, the fractions I and II are also the weighing factors for the redistribution of the locked-in light. This is below also indicated in a table.
[0045]n_rod = 1.84,n_CPC = 1.52Light fractionsn_rod = 1.84,n_rod = 1.84,redistributedin rectangular rodn_CPC = 1.84n_CPC = 1.52Locked-InI non-TIR32%32%32% + 11% = 43%II TIR-to-Nose68%43%43% + 14% = 57%III Locked-in TIR—25%redistributed
[0046]Rods (up to now with rectangular cross section) are expected to have a maximum optical efficiency depending on the refractive index of the rod. If the optical efficiency is defined as the ratio of luminescent material light that goes into the CPC over the total luminescent material light generated in the elongated light transmissive body, the believed maximum is 68% in case of n_rod=n_CPC=1.84, and is lower, about 57%, in case of a rod with n_rod=1.84 and n_CPC=1.52 (glass). In the latter case, part of the locked-in fraction (III) is converted into the TIR-to-Nose fraction (II) via scattering or via re-absorption and re-emission.
[0047]Hence, it is an aspect of the invention to provide an alternative lighting device comprising a luminescent concentrator, which preferably further at least partly obviates one or more of above-described drawbacks and/or which may have a relatively higher efficiency. The present invention may have as object to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.
[0048]It appears that in a round rod the three light fractions have different values. If the light is generated somewhere in the heart of the rod, the light fraction I (non-TIR) is high. The light fraction II is still the same as for a rectangular rod, and Locked-in Light is virtually not present. Further, it surprisingly appears that with n_rod=1.84, the light fraction that is escaping from the rod directly (non-TIR) is only 16% if it is generated in the skin of the rod (skin thickness=0). If light is generated on the skin, the non-TIR cone angles to both sides perpendicular to the skin are identical for the round rod and rectangular rods, which can be proven by simple goniometry. For that reason, the non-TIR fraction for skin generated light is exactly half of the non-TIR fraction in a rectangular rod. The non-TIR loss has been modelled analytically for round and rectangular rods. Assuming the light to be generated at a distance x from the wall, the non-TIR fraction increases with the relative distance to the wall, as expressed in the ratio x/r, which is the case for round rods only. Further, it surprisingly appears that up to about x/r=0.4 there is lower non-TIR losses for round rounds as compared to rectangular rods. For a round rod of 2 mm diameter this is up to a depth of 0.4 mm.
[0049]The afore-mentioned consideration may not only apply to essentially massive CPCs as optical element downstream of the luminescent concentrator, but may also apply for other optical elements, such as a dome, a wedge-shaped structure, a hollow CPC, et cetera.
[0050]Hence, the invention provides in an aspect a luminescent element comprising an elongated light transmissive body, the elongated light transmissive body comprising a side face, wherein (i) the elongated light transmissive body comprises a luminescent material configured to convert at least part of a light source light selected from one or more of the UV, visible light, and IR received by the elongated light transmissive body into luminescent material radiation; (ii) the side face comprises a curvature with a radius (r); and (iii) the concentration of the luminescent material is chosen such that at least 50%, such as at least 60%, like at least 70% of the light, especially at least 80% of light, at one or more radiation wavelengths is absorbed within a first length (x) from the side face, wherein in specific embodiments especially x/r≤0.4 applies.
[0051]In the case of hollow light transmissive bodies or in the case of light transmissive bodies with a high luminescent material concentration in an outer region of the body and a lower concentration (including zero) at a more inner part of the body, such as a core, the concentration of the luminescent material may be lower, as radiation that is not absorbed may escape from the body but be absorbed again. Hence, assuming perpendicular irradiation of the side face from external of the light transmissive body, thus not from inside in the cavity, the concentration of the luminescent material may also be chosen such that at least 50% of the radiation, such as at least 60% of the radiation of the light source, like at least 70%, especially at least 80%, is absorbed. Here, the perpendicular radiation may thus especially include propagating through a first region with relatively high concentration and before emanating from another part of the body also propagation through a second region with relatively high concentration. Hence, in specific embodiments also for this configuration the concentration of luminescent material may be chosen such that in total at least 50%, such as at least 60%, like at least 70%, such as especially at least 80%, is absorbed within a first length (x) from the (outer) side face, wherein in specific embodiments especially x/r≤0.4 applies, where r refers to the radius of the outer surface of the hollow light transmissive body.
[0052]With such element it may be possible to provide in a more efficient way light, escaping from the transmissive body, when the transmissive body is illumination with light source light that is at least partially converted by the luminescent material comprised by the transmissive body. The outcoupling may be higher than in luminescent bodies having a rectangular cross-section.
[0053]Especially, the concentration of the luminescent material is chosen such that at least 50%, such as at least 60%, like at least 70% of the light, especially at least 80% of light, at one or more radiation wavelengths is absorbed within a first length (x) from the side face, wherein especially x/r≤0.4 applies.
[0054]In embodiments, the radius (r) is selected from the range of 0.1-200 mm, such as 0.2-200 mm, like especially 0.25-50 mm, such as 0.5-50 mm. When a blue light source is applied, especially the luminescent material absorbs in the blue. Or, the other way around, when the luminescent material absorbs in the blue, especially a light source may be applied that emits in the blue. In specific embodiments, the concentration of the luminescent material is chosen such that at least 90% of light in the blue is absorbed within the first length (x) from the side face, wherein x/r≤0.4 applies, and wherein the first length (x) is equal to or less than 5 mm. In specific embodiments, x/r≤0.3, such as x/r≤0.2. However, especially, x/r≥0.01, such as x/r≥0.02.
[0055]Here, especially at least the side face may be irradiated by the light source.
[0056]As indicated above, the side face comprises a curvature with a radius (r). When the body comprises a plurality of side faces, such as in the case of a body having a rectangular with one face being curved, at least the curved side face may be irradiated with the light source. One or more side faces may comprise a radius, which may be different or which may be alike; especially they may be the same. The radius is especially defined in relation to a body axis. Further, a side face may comprise a plurality of curvature. In general, however, the number of different curvatures for a single side face are limited, or the radii are found within a limited range (such as differing from each other within about 5% from a mean value), or there is only a single radius value.
[0057]In specific embodiments, the side face has a convex shape. Further, especially a plurality of convex shaped side face may be available. In yet other embodiments, however, there is essentially a single side face that has a curvature. This is especially the case when a rod is applied having a circular cross-section.
[0058]In embodiments the elongated body of the luminescent element especially comprises a first side face and a second side face, one of these being convex and one of these being concave, with the latter defining a cavity. For instance, this may be the case when a concave shaped or convex shape body is applied, by which one a convex and a concave side face may in embodiments be available. Especially, in embodiments the elongated light transmissive body may have a tubular shape having a cavity surrounded by the elongated light transmissive body. For yet even higher outcoupling efficiencies, the cavity may be filled with (another material). Therefore, in embodiments at least part of the cavity, especially the entire cavity, comprises a light transmissive material, differing in composition from the composition of the material of the elongated light transmissive body. In specific embodiments, the light transmissive material in the cavity has an index of refraction equal to or lower than the light transmissive material of the light transmissive body (but higher than air). An example of a suitable filling may comprise one or more of MgF2 or CaF2, silicone, glass or transparent ceramics like spinel, poly crystalline alumina or sapphire, YAG or a material similar to the first body material, but without the phosphor. The materials should be transparent, but could be amorphous, poly-crystalline or single crystalline.
[0059]In this way, a body may be obtained with a (virtual) outer shell with a high concentration of the luminescent material, and a core with a lower concentration of the luminescent material (including essentially no luminescent material). For instance, a cerium containing garnet may be provided as tube, with a filling of essentially the same garnet, without cerium. Such body with a core-shell configuration of the luminescent material, with a higher concentration luminescent material in the shell and a lower concentration (including zero) at the core may in embodiments have a distribution which is essentially defined by one or more specific regions with a high concentration, but all regions essentially having the same concentration, and one or more specific regions with a low concentration (including zero), but also all these regions essentially having the same concentration. This might in embodiments be a kind of binary distribution. In other embodiments, the distribution may have a gradation, with a gradual decrease from a relatively highly concentrated region to a relatively low concentration (including in embodiments zero).
[0060]In specific embodiments, the light transmissive material in the cavity has a substantially equal index of refraction to the material of the light transmissive body. This may allow a substantial absence of scattering of light at the interface. Such system can be realized by e.g. co-extrusion of starting materials (such as green masses) with and without cerium, respectively that are co-sintered into a monolithic component.
[0061]Hence, in embodiments the refractive index throughout the elongated light transmissive body may be essentially constant, but the activator (such as trivalent cerium) may essentially be present only in a shell, which is configured as radiation input face (which may also be indicated as light entrance window or light entrance face).
[0062]The elongated body may be, as indicated above, tubular. However, the elongated body may also be massive, and may e.g. have an essentially circular cross-section. Therefore, in embodiments the elongated light transmissive body has an axis of elongation (BA) and a circular cross-section perpendicular to the axis of elongation (BA).
[0063]Here, especially the elongated light transmissive body has a first face (or “first end face”) and a second face (or “second end face”) defining a length (L) of the elongated light transmissive body; wherein the side face comprises the radiation input face, wherein the second face comprises the radiation exit window.
[0064]Assuming e.g. solid round elongated light transmissive bodies, light that is generated in the “skin” of the rod may be carried by the elongated light transmissive body acting as a kind of light guide. The light that is aligned with the main axis (“body axis” or “axis of elongation”) or under small angles with the main axis is coupled out via the CPC. There is also a large portion of the light that moves along the circumference of the rod with only a small component along the main axis, so these rays follow a kind of a screw pattern. Whe
具体实施方式：
[0255]The schematic drawings are not necessarily to scale.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0256]A light emitting device according to the invention may be used in applications including but not being limited to a lamp, a light module, a luminaire, a spot light, a flash light, a projector, a (digital) projection device, automotive lighting such as e.g. a headlight or a taillight of a motor vehicle, arena lighting, theater lighting and architectural lighting.
[0257]Light sources which are part of the embodiments according to the invention as set forth below, may be adapted for, in operation, emitting light with a first spectral distribution. This light is subsequently coupled into a light guide or waveguide; here the light transmissive body. The light guide or waveguide may convert the light of the first spectral distribution to another spectral distribution and guides the (converted) light to an exit surface.
[0258]An embodiment of the lighting device as defined herein is schematically depicted in FIG. 1a. FIG. 1a schematically depicts a lighting device 1 comprising a plurality of solid state light sources 10 and a luminescent concentrator 5 comprising an elongated light transmissive body 100 having a first face 141 and a second face 142 defining a length L of the elongated light transmissive body 100. The elongated light transmissive body 100 comprising one or more radiation input faces 111, here by way of example two oppositely arranged faces, indicated with references 143 and 144 (which define e.g. the width W), which are herein also indicated as edge faces or edge sides 147. Further the light transmissive body 100 comprises a radiation exit window 112, wherein the second face 142 comprises the radiation exit window 112. The entire second face 142 may be used or configured as radiation exit window. The plurality of solid state light sources 10 are configured to provide (blue) light source light 11 to the one or more radiation input faces 111. As indicated above, they especially are configured to provide to at least one of the radiation input faces 111 a blue power Wopt of in average at least 0.067 Watt/mm2. Reference BA indicates a body axis, which will in cuboid embodiments be substantially parallel to the edge sides 147. Reference 140 refers to side faces or edge faces in general.
[0259]The elongated light transmissive body 100 may comprise a ceramic material 120 configured to wavelength convert at least part of the (blue) light source light 11 into converter radiation 101, such as at least one or more of green and red converter radiation 101. As indicated above the ceramic material 120 comprises an A3B5O12:Ce3+ ceramic material, wherein A comprises e.g. one or more of yttrium (Y), gadolinium (Gd) and lutetium (Lu), and wherein B comprises e.g. aluminum (Al). References 20 and 21 indicate an optical filter and a reflector, respectively. The former may reduce e.g. non-green light when green light is desired or may reduce non-red light when red light is desired. In addition, the former may be used as well to reflect light back into the transmissive body or waveguide that is not desired as output light from the elongated light transmissive body that subsequently may get re-absorbed in the ceramic material. For instance, a dichroic filter may be applied. The latter may be used to reflect light back into the light transmissive body or waveguide, thereby improving the efficiency. Note that more reflectors than the schematically depicted reflector may be used. Note that the light transmissive body may also essentially consist of a single crystal, which may in embodiments also be A3B5O12:Ce3+.
[0260]The light sources may in principle be any type of light source, but is in an embodiment a solid state light source such as a Light Emitting Diode (LED), a Laser Diode or Organic Light Emitting Diode (OLED), a plurality of LEDs or Laser Diodes or OLEDs or an array of LEDs or Laser Diodes or OLEDs, or a combination of any of these. The LED may in principle be an LED of any color, or a combination of these, but is in an embodiment a blue light source producing light source light in the UV and/or blue color-range which is defined as a wavelength range of between 380 nm and 490 nm. In another embodiment, the light source is an UV or violet light source, i.e. emitting in a wavelength range of below 420 nm. In case of a plurality or an array of LEDs or Laser Diodes or OLEDs, the LEDs or Laser Diodes or OLEDs may in principle be LEDs or Laser Diodes or OLEDs of two or more different colors, such as, but not limited to, UV, blue, green, yellow or red.
[0261]The light sources 10 are configured to provide light source light 11, which is used as pump radiation 7. The luminescent material 120 converts the light source light into luminescent material radiation 8 (see also FIG. 1e). Light escaping at the light exit window is indicated as converter radiation 101, and will include luminescent material radiation 8. Note that due to reabsorption part of the luminescent material radiation 8 within the luminescent concentrator 5 may be reabsorbed. Hence, the spectral distribution may be redshifted relative e.g. a low doped system and/or a powder of the same material. The lighting device 1 may be used as luminescent concentrator to pump another luminescent concentrator.
[0262]As indicated above, the element may include dichroic optical element. Further, the element may include other elements such as e.g. an anti-reflex (AR) coating on one or more surfaces of the elongated light transmissive body and of the optical element (at the second face side). It may be advantageous to have an AR coating for the pump light at the optical entrance window(s), and/or to have an AR coating for the converted light at the light emission window(s). In addition, reflective coatings for the converted light may be applied to the surface areas other than the light extraction window.
[0263]FIGS. 1a-1b schematically depict similar embodiments of the lighting device. Further, the lighting device may include further optical elements, either separate from the waveguide and/or integrated in the waveguide, like e.g. a light concentrating element, such as a compound parabolic light concentrating element (CPC). The lighting devices 1 in FIG. 1b further comprise a collimator 24, such as a CPC.
[0264]As shown in FIGS. 1a-1b and other Figures, the light guide has at least two ends, and extends in an axial direction between a first base surface (also indicated as first face 141) at one of the ends of the light guide and a second base surface (also indicated as second face 142 or “nose”) at another end of the light guide.
[0265]FIG. 1c schematically depicts some embodiments of possible ceramic bodies or crystals as waveguides or luminescent concentrators. The faces are indicated with references 141-146.
[0266]The first variant, a plate-like or beam-like light transmissive body has the faces 141-146. Light sources, which are not shown, may be arranged at one or more of the faces 143-146 (general indication of the edge faces is reference 147). Light sources, not shown, may be configured to provide radiation to one or more edge faces or side faces selected from faces 143-146. Alternatively or additionally, Light sources, not shown, may be configured to provide radiation to the first face 141 (one of the end faces).
[0267]The second variant is a tubular rod, with first and second faces 141 and 142, and a circumferential face 143. Light sources, not shown, may be arranged at one or more positions around the light transmissive body. Such light transmissive body will have a (substantially) circular or round cross-section. The third variant is substantially a combination of the two former variants, with two curved and two flat side faces.
[0268]In the context of the present application, a lateral surface of the light guide should be understood as the outer surface or face of the light guide along the extension thereof. For example in case the light guide would be in form of a cylinder, with the first base surface at one of the ends of the light guide being constituted by the bottom surface of the cylinder and the second base surface at the other end of the light guide being constituted by the top surface of the cylinder, the lateral surface is the side surface of the cylinder. Herein, a lateral surface is also indicated with the term edge faces or side 140.
[0269]The variants shown in FIG. 1c are not limitative. More shapes are possible; i.e. for instance referred to WO2006/054203, which is incorporated herein by reference. The ceramic bodies or crystals, which are used as light guides, generally may be rod shaped or bar shaped light guides comprising a height H, a width W, and a length L extending in mutually perpendicular directions and are in embodiments transparent, or transparent and luminescent. The light is guided generally in the length L direction. The height H is in embodiments <10 mm, in other embodiments <5 mm, in yet other embodiments <2 mm. The width W is in embodiments <10 mm, in other embodiments <5 mm, in yet embodiments <2 mm. The length L is in embodiments larger than the width W and the height H, in other embodiments at least 2 times the width W or 2 times the height H, in yet other embodiments at least 3 times the width W or 3 times the height H. Hence, the aspect ratio (of length/width) is especially larger than 1, such as equal to or larger than 2, such as at least 5, like even more especially in the range of 10-300, such as 10-100, like 10-60, like 10-20. Unless indicated otherwise, the term “aspect ratio” refers to the ratio length/width. FIG. 1c schematically depicts an embodiment with four long side faces, of which e.g. two or four may be irradiated with light source light.
[0270]The aspect ratio of the height H:width W is typically 1:1 (for e.g. general light source applications) or 1:2, 1:3 or 1:4 (for e.g. special light source applications such as headlamps) or 4:3, 16:10, 16:9 or 256:135 (for e.g. display applications). The light guides generally comprise a light input surface and a light exit surface which are not arranged in parallel planes, and in embodiments the light input surface is perpendicular to the light exit surface. In order to achieve a high brightness, concentrated, light output, the area of light exit surface may be smaller than the area of the light input surface. The light exit surface can have any shape, but is in an embodiment shaped as a square, rectangle, round, oval, triangle, pentagon, or hexagon.
[0271]Note that in all embodiments schematically depicted herein, the radiation exit window is especially configured perpendicular to the radiation input face(s). Hence, in embodiments the radiation exit window and radiation input face(s) are configured perpendicular. In yet other embodiments, the radiation exit window may be configured relative to one or more radiation input faces with an angle smaller or larger than 90°.
[0272]FIG. 1c schematically depict some basic embodiments. Especially however, the herein described specific embodiments are applied, such as wherein the bodies 100 have circular cross-section, but have a shell-like distribution of the luminescent material and/or are hollow, and/or wherein the bodies have facets at one or more end faces and/or wherein the bodies taper over at least part of their length.
[0273]Note that, in particular for embodiments using a laser light source to provide light source light, the radiation exit window might be configured opposite to the radiation input face(s), while the mirror 21 may consist of a mirror having a hole to allow the laser light to pass the mirror while converted light has a high probability to reflect at mirror 21. Alternatively or additionally, a mirror may comprise a dichroic mirror.
[0274]FIG. 1d very schematically depicts a projector or projector device 2 comprising the lighting device 1 as defined herein. By way of example, here the projector 2 comprises at least two lighting devices 1, wherein a first lighting device (1a) is configured to provide e.g. green light 101 and wherein a second lighting device (1b) is configured to provide e.g. red light 101. Light source 10 is e.g. configured to provide blue light. These light sources may be used to provide the projection (light) 3. Note that the additional light source 10, configured to provide light source light 11, is not necessarily the same light source as used for pumping the luminescent concentrator(s). Further, here the term “light source” may also refer to a plurality of different light sources. The projector device 2 is an example of a lighting system 1000, which lighting system is especially configured to provide lighting system light 1001, which will especially include lighting device light 101. Such a lighting system may further comprise a controller for controlling the light source(s).
[0275]High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection.
[0276]For this purpose, it is possible to make use of so-called luminescent concentrators where shorter wavelength light is converted to longer wavelengths in a highly transparent luminescent material. A rod of such a transparent luminescent material can be used and then it is illuminated by LEDs to produce longer wavelengths within the rod. Converted light which will stay in the luminescent material such as a doped garnet in the waveguide mode and can then be extracted from one of the surfaces leading to a luminance and/or radiance gain (FIG. 1e).
[0277]High-brightness LED-based light source for beamer applications appear to be of relevance. For instance, the high brightness may be achieved by pumping a luminescent concentrator rod by a discrete set of external blue LEDs, whereupon the phosphor that is contained in the luminescent rod subsequently converts the blue photons into green or red photons. Due to the high refractive index of the luminescent rod host material (typically˜1.8) the converted green or red photons are almost completely trapped inside the rod due to total internal reflection. At the exit facet of the rod the photons are extracted from the rod by means of some extraction optics, e.g. a compound parabolic concentrator (CPC), or a micro-refractive structure (micro-spheres or pyramidal structures). As a result the high luminescent power that is generated inside the rod can be extracted at a relatively small exit facet, giving rise to a high source brightness, enabling (1) smaller optical projection architectures and (2) lower cost of the various components because these can be made smaller (in particular the, relatively expensive, projection display panel).
[0278]When luminescent light is generated in an elongated light transmissive body, three light fractions can be discerned, namely[0279]I. Non-TIR light in the cones that are directly transmitted through one of the four long sides.[0280]II. Light in the cones that are aligned with the long axis (z-axis) of the rod, this light sometimes is called TIR-to-Nose light, as this light is in TIR in the rod until it hits the CPC, and is transmitted through the CPC. The rays that go into the CPC have an angle with the z-axis that is smaller than the critical TIR angle that holds for the n_rod-n_CPC combination. The light in the cone that is directed towards the tail reflects at the tail via TIR or via the mirror, and also leaves the rod at the CPC.[0281]III. The remaining light fraction is in TIR and—in theory, in a perfect rod—these rays cannot escape from the rod. This fraction is sometimes called Locked-in TIR light (after the Locked-in syndrome).
[0282]If in the round rod the light is generated in the skin, the light fraction II (TIR-to-Nose) remains unchanged, but fractions I and III change dramatically. FIG. 2a schematically shows the situation that light is generated in the center and FIG. 2b schematically shows the situation that light is generated close to the wall. In both cases, the refractive index of the body material of the elongated light transmissive body was chosen to be 1.84 and of the optical element (CPC like optical element) was chosen to be 1.52. With n_rod=1.84, the light fraction that is escaping from the rod directly (non-TIR) is only 16% if it is generated in the skin of the rod (skin thickness=0). If light is generated on the skin, the non-TIR cone angles to both sides perpendicular to the skin are identical for the round rod and rectangular rods, which can be proven by simple goniometry. For that reason, the non-TIR fraction for skin generated light is exactly half of the non-TIR fraction in a rectangular rod. The non-TIR loss has been modelled analytically for round and rectangular rods. Assuming the light to be generated at a distance x from the wall, the non-TIR fraction increases with the relative distance to the wall, as expressed in the ratio x/r, wherein r is the radius, which is the case for round rods only. Up to x/r=0.4 there is lower non-TIR losses for round rods as compared to rectangular rods. For a round rod of 2 mm diameter this is up to a depth of 0.4 mm; see FIG. 2c. The radius is indicated with reference y.
[0283]With increasing depth of light generation, the non-TIR fraction increases up to the 57% non-TIR level of the case with light generated in the center. But with low skin thickness, there is a substantial increase of the optical efficiency of the rod as compared to the rectangular rod. For rectangular rods, the light fractions are essentially independent of the position of light generation. Hence, in an ideal case with light generation on the surface of the round rod, compared to a rectangular rod the efficiency may increase substantially, such as from 68% (rectangular) to 84% (round) (with n_rod=n_CPC=1.84), or such as from 57% (rectangular) to 72% (round) (with n_rod=1.84, n_CPC=1.52). This can be indicated in the following table:
[0284]n_rod = 1.84,n_CPC = 1.52Light fractionsn_rod = 1.84,n_rod = 1.84,redistributedin round rodn_CPC = 1.84n_CPC = 1.52Locked-InI non-TIR16%16%16% + 12% = 28%II TIR-to-Nose84%43%43% + 29% = 72%III Locked-in TIR—41%Redistributed
[0285]A small absorption length for blue light is the key to having light generated in the skin only. For that reason, an aspect of the invention is that the phosphor content is sufficiently high. For single crystal LuAG a phosphor concentration of Ce %=0.16-0.25% may lead to an absorption length of about 0.3 mm-0.2 mm. In order to get an absorption length of 0.1 mm, about 0.5% Ce may thus be needed.
[0286]Another way of enabling light generation in the skin is by making a tubular rod, see FIG. 2d. In this case the light guiding effect is effective over the full thickness of the ‘ring’. The phosphor content is allowed to be lower as there cannot be phosphor-emitted light from the core. In an application one should set a limitation to the minimum phosphor content as e.g. substantial blue light transmission through the full rod should be avoided. FIG. 2d schematically depicts a non-limiting number of embodiments in cross-sectional views (see also FIG. 6f), with a tubular body 100 having a circular cross-section, a tubular body with a rectangular (square) cross-section, and a tubular body with a round cross-section, wherein by way of example the cavities, indicated with reference 1150, in the former two variants may be filled with a material 121, which especially may have in embodiments a refractive index lower than the refractive index of the material of the elongated (tubular) body (but higher than air). The distance between the bodies, indicated with reference d4 in variant III, may differ along the body axis BA (see also FIG. 5b). In embodiments, especially where the cavity 1150 is filled with a material having essentially the same index of refraction as the material of the adjacent outer body 100, then there may be physical contact (i.e. d4=0 μm). The cavity may in embodiments also at least partly be filled with another body 100; in such embodiment a core-shell configuration may be obtained (see also FIGS. 4a-4b). When the cavity comprises a solid element, such as a body (see also FIG. 4a), the cross-sectional symmetry of the internal body may be different from the external body, though especially they may be the same. In the former variant, d4 may vary over the cross-section. Referring to FIG. 2d, but e.g. also 2e, 5b, transmission perpendicular to the body 100 of light leads to a double pass. The total transmission through the body under perpendicular radiation with light having a wavelength of interest, such as e.g. the wavelength at maximum emission of the luminescent material, is at maximum 50%.
[0287]With the embodiment of FIG. 5b, the advantages of a hollow (with circular cross-section) variant, or a variant wherein a concentration of the luminescent material (or activator) is variable over the distance to the surface, is combined with the variant of tapering, wherein light is concentrated in a small area. Thereby, the ring shape distribution of the light may essentially be reduced. With the downstream optical element, e.g. the beam may be shaped.
[0288]In specific embodiments, including the embodiment schematically depicted in FIGS. 3b, 3e, 3g (top) and 5b, wherein hallow bodies 100 are applied: when the hollow body does not contain another body or material in the cavity, at the inside a reflector may be arranged.
[0289]Hence, especially the following conditions may be applied:
[0290]a solid rod: round, oval or elliptical in cross section externally; with sufficient phosphor content to have an absorption length ≤0.4 rod radius; or
[0291]a tubular rod, round, oval or elliptical in cross section, with limited wall thickness, such that inner radius ≥0.6 outer radius; with sufficient phosphor content to have absorption length≤wall thickness.
[0292]Another way of enabling light generation in the skin is by realization of a body 100 in which the luminescent material (or activator) concentration is localized near the outer surface. In this case, the refractive index is essentially constant throughout the complete body. Such embodiments is schematically depicted in FIG. 2e.
[0293]FIG. 2e schematically depicts a variant wherein the luminescent element 5 further comprises a first reflector 21 and/or a second reflector 22. The elongated light transmissive body 100 has a first face 141 and a second face 142 defining a length L of the elongated light transmissive body 100; wherein the second face 142 comprises a first radiation exit window 112. The first reflector 21 is configured at the first face 141 and is configured to reflect radiation back into the elongated light transmissive body 100. The second reflector 22 has a cross-section smaller than the radiation exit window 112, wherein the first reflector 22 is configured to reflect radiation back into the light transmissive body 100.
[0294]Here, the distances between the optical elements 21 and 22 with the light transmissive body are indicated with references d1 and d2, respectively. Preferably, they have no physical (or optical) contact to allow TIR for rays with high angle of incidence and only reflect low angle of incidence rays via the mirror. Distances d1 and d2 may e.g. be in the order of 1-50 μm for visible radiation. As indicated above, values of these distances may be indicated as average values.
[0295]In other embodiments, however, there may be physical contact between the body and the optical element 21 (if available) and/or the optical element 22 (if available). For instance, upon pressing the mirror to the rod, a bare minimum of real material-material contact area is inevitable from contact force and material hardness. In case of optical contact, more rays hit the mirror, but the additional loss is still limited if the reflectivity of the mirror is high. Further, the distance between a light emitting surface 13 of the light source 10 and the light transmissive element is indicated with reference d3. Hence, these distances d1, d2, and d3 may each independently be chosen of a range of at least 1 μm, such as at least 2 μm.
[0296]One or more of the end faces may be facetted or may have other modulations, or may have one or more oblique sides, see FIGS. 3a-3f. For instance, one or more of the first face 141 and the second face 142 comprise a plane 1140 comprising surface modulations 1141 thereby creating different modulation angles β relative to the respective plane 1140; these angles may be equal to or smaller than e.g. about 45°, such as at maximum 40°, like in embodiments at maximum 30°, such as equal to or smaller than about 25° (see e.g. FIG. 3d). Further, in embodiments β is especially at least 15°, such as at least 20°. Especially, the plane 1140 comprises n/cm2 facets 1142 as modulations 1141, wherein n is selected from the range of 2-2000, such as 4-500. Further, in embodiments, as schematically depicted, there are at least 2 facets 1142 having different modulation angles β, such as at least four. There may also be a continuous modulation, see FIG. 3c, wherein a kind of sinusoidal modulation is available.
[0297]The body 100 may have a square cross-section or a rounded cross-section. In the latter variant, the modulations are especially modulations parallel to the radius radii, and not deviations from the radius radii. Thus, the modulations 1141 may have angles γ relative to perpendiculars r1 to the axis of elongation BA selected from the range of 0-90°, such as in embodiments up to 35°, like in the range of 15-35°, more like in the range of 25-35° see also FIGS. 3f and 3g. The outcoupling of the luminescence in variants I-II can be increased with 1-5 percent points using facets, such as four facets. The outcoupling of the luminescence in variant III can be increased with 5-10 percent points using facets, such as four facets. Note that in variant I (and III) there is some radial distortion. FIGS. 3b and 3e, and optionally FIG. 3d, schematically depict facets provided to an end face of a hollow (tubular) body 100. FIG. 3f, and optionally FIG. 3d, schematically depicts facets to an end face of a cylindrical body.
[0298]FIG. 3g schematically depict three variants of bodies wherein the first face 141 and/or the second face 142 (here, a single face is depicted) comprises a plurality of facets 1140, here each having four facets 1140. Variant I shows a hollow body 100 having a round cross-section, variant 2 schematically depicts a body 100 having a rectangular cross-section, and variant III schematically depicts a body 100 having a round cross-section. Best results may be obtained with β in the range of 15-45°, such as 20-40°, even more such as 25-35°. In a preferred embodiment, the bodies (variant I, II and III) of FIG. 3a-g further comprise a reflective surface (not shown in FIG. 3a-g) facing the first face (141). The reflective surface is conformal with the shape of the first face (141) and is not in direct contact with the first face (141). The gap between the reflective surface and the first face (141) may be filled with air or with a material that has a relative low refractive index compared to the material of the elongated light transmissive body (100).
[0299]Hence, when especially referring to bodies 100 having a circular cross-section, A primary function of the modulations, such as facets, would be a β modulation (tangential direction), but for a limited number of modulations, such as especially facets, there may also be (significant) γ modulation. The embodiments of FIG. 3g all have an efficiency increase of about 5-10% relative to bodies 100 without the modulations (here four facets).
[0300]Especially, for one or more modulations, such as for one or more facets, especially for essentially all modulations, such as essentially all facets, the ratio of β/γ≥0.8, such as especially β/γ≥1.0, like β/γ≥1.2.
[0301]An advantage of a hollow elongated body is that no scattering can take place in the center of the rod. It appears that light scattering in the center of a round rod leads to relatively high light losses and should be avoided. However, with a hollow elongated light transmissive body the inside wall introduces a new source of light scattering which can lower the performance of the elongated light transmissive body if the scattering is significant. But it is hard and expensive to polish the inside rod wall to a surface smoothness with only low scattering.
[0302]With a transparent filling material the light scattering at the inside wall is reduced, as more rays that hit the inside wall are transmitted through the interface. The closer the refractive indices of rod and filling material are, the smaller the change in light direction upon transmission through the interface. Further, with a given (high index) rod material, the critical TIR angle depends on the refractive index of the filling material, the more close n_filler is to n_rod, the larger the critical TIR angle and the more transmission takes place, while transmitted light is scattered less than reflected light. Also, the Fresnel reflections depend on the refractive indices of both materials, the more close n_filler is to n_rod, the lower the Fresnel reflections are (which are subjected to scattering). Scattering at the inside wall is completely vanished if n_filler=n_rod. But also the light guiding of the inside wall in no longer there.
[0303]In view of the light guiding effect of the inside wall it may be advantageous to have a filling material with a refractive index that is lower than that of the rod.
[0304]Hence, the following features may be of relevance: a hollow elongated light transmissive body, a filling material that is essentially fully transparent, with a very low scatter level, essentially no air bubbles or other inclusions in the filling material, and a refractive index of the filling material that is in between the refractive indices of air and the elongated light transmissive body.
[0305]Further, a rod-in-rod concept may be applied, see FIGS. 4a-4b.
[0306]For instance, rods having the same length and concentration of phosphor fixed along the rod can be applied. Then, the spectral distribution may not be tunable when irradiation is via the outer rod. Especially, in such embodiments where the light sources are configured external of the rod assembly, the phosphor concentration of outer rod should be low enough that part of the light source light, such as blue LED light can hit the inner rod.
[0307]In embodiments, for blue light one can use high power LED at beginning of the rod which can be just a light guide. Alternatively or additionally, a LED with e.g. 405 nm can be used that pass the green and red rod and hit the center rod which absorbs 405 nm and exits ˜470 nm blue.
[0308]In embodiments, the concentration of the phosphor varies along the rod. If phosphor concentration varies along the rod; more or less blue light can hit the red rod, when irradiation is via the outer rod. Adapting current depending on location of the blue LED, spectrum can be changed.
[0309]For extraction of light from the light transmissive body, a CPC (Compound Parabolic concentrator) can be used. For best extraction, the refractive index of the CPC should match with refractive index of the rod. The attachment of this CPC to the HLD rod is quite a challenge regarding matching refractive indices rod, glue, CPC and mechanical strength. By making the rod from one piece the last part of the rod can be made completely tapered, in embodiments with increasing diameter for increasing distance from the cylindrical luminescent converter component to extract the light from the end side, or in other embodiments with decreasing diameter for increasing distance from the cylindrical luminescent converter to extract the light from the tapered side surface, by which light can be extracted as also collimated by which no CPC is needed which is a big advantage. Another possibility is partly tapering of the rod and adding a CPC after the tapered part. An advantage may be that extracted light has much lower etendue or a higher brightness may be achieved (than with a tapered light transmissive body), and still the controlled collimation of light with CPC may be obtained.
[0310]Both options worked best with hollow cylindrical or elliptical shaped rods in which light is generated close to the outer wall of the rod and with additional structures on mirror opposite to the light extraction.
[0311]Both figures shows embodiments of a luminesce