Light concentrator module

Abstract

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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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:

(2) FIGS. 1a-1e schematically depict some aspects of the invention; and

(3) FIGS. 2a-2e schematically depict some embodiments;

(4) FIGS. 3a-3g schematically depict some embodiments of facets;

(5) FIGS. 4a-4b schematically depict a core-shell embodiment;

(6) FIGS. 5a-5b schematically depict some tapered embodiments;

(7) FIGS. 6a-6e schematically depict some specifically shaped light transmissive bodies; FIG. 6f schematically depict some variants of cross-sections of possible light transmissive bodies; FIG. 6g schematically depict some possible basic shapes of light transmissive bodies (in cross-sectional view);

(8) FIGS. 7a-7d are directed to some embodiments of optical elements; and

(9) FIGS. 8a-8f schematically depict some aspects of light transmissive bodies, optionally with optical elements and/or a mixing portion.

(10) The schematic drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(11) 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.

(12) 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.

(13) 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 W.sub.opt of in average at least 0.067 Watt/mm.sup.2. Reference BA indicates a body axis, which will in cuboid embodiments be substantially parallel to the edge sides 147. Reference 140 refers to side faces or edge faces in general.

(14) 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 A.sub.3B.sub.5O.sub.12:Ce.sup.3+ ceramic material, wherein A comprises e.g. one or more of yttrium (Y), gadolinium (Gd) and lutetium (Lu), and wherein B comprises e.g. aluminum (Al). References 20 and 21 indicate an optical filter and a reflector, respectively. The former may reduce e.g. non-green light when green light is desired or may reduce non-red light when red light is desired. 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 A.sub.3B.sub.5O.sub.12:Ce.sup.3+.

(15) 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.

(16) 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.

(17) 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.

(18) 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.

(19) 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.

(20) 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.

(21) 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).

(22) 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.

(23) 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.

(24) 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.

(25) 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.

(26) 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.

(27) 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.

(28) 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.

(29) 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).

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

(31) 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).

(32) 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 (typically1.8) 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).

(33) When luminescent light is generated in an elongated light transmissive body, three light fractions can be discerned, namely I. Non-TIR light in the cones that are directly transmitted through one of the four long sides. 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. III. The remaining light fraction is in TIR andin theory, in a perfect rodthese rays cannot escape from the rod. This fraction is sometimes called Locked-in TIR light (after the Locked-in syndrome).

(34) 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.

(35) 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:

(36) TABLE-US-00002 n_rod = 1.84, n_CPC = 1.52 Light fractions n_rod = 1.84, n_rod = 1.84, redistributed in round rod n_CPC = 1.84 n_CPC = 1.52 Locked-In I non-TIR 16% 16% 16% + 12% = 28% II TIR-to-Nose 84% 43% 43% + 29% = 72% III Locked-in TIR 41% Redistributed

(37) 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.

(38) 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 m). 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%.

(39) 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.

(40) 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.

(41) Hence, especially the following conditions may be applied:

(42) 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

(43) 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 lengthwall thickness.

(44) 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.

(45) 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.

(46) 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 m for visible radiation. As indicated above, values of these distances may be indicated as average values.

(47) 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 m, such as at least 2 m.

(48) 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 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 is especially at least 15, such as at least 20. Especially, the plane 1140 comprises n/cm.sup.2 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 , such as at least four. There may also be a continuous modulation, see FIG. 3c, wherein a kind of sinusoidal modulation is available.

(49) 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 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.

(50) 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 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).

(51) Hence, when especially referring to bodies 100 having a circular cross-section, A primary function of the modulations, such as facets, would be a modulation (tangential direction), but for a limited number of modulations, such as especially facets, there may also be (significant) 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).

(52) 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 /0.8, such as especially /1.0, like /1.2.

(53) 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.

(54) 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.

(55) 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.

(56) 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.

(57) Further, a rod-in-rod concept may be applied, see FIGS. 4a-4b.

(58) 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.

(59) 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.

(60) 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.

(61) 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.

(62) 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.

(63) Both figures shows embodiments of 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; wherein the elongated light transmissive body 100 has a length L; the elongated light transmissive body 100 is hollow over at least part of the length L thereby defining a cavity 1150.

(64) In FIG. 4a, the elongated light transmissive body 100 is tubular shaped. Further, the elongated light transmissive body 100 has a tubular shape having a cavity 1150 surrounded by the elongated light transmissive body.

(65) Also, by way of example in FIG. 4b, the luminescent element 5 further comprising an optical element 24 optically coupled to the elongated light transmissive body 100, here a dome. In an alternative embodiment, a conical structure may be applied. Such conical structure may taper in the direction of a radiation entrance window 211 of the optical element (i.e. in the direction of the second face 142 of the light transmissive body 100 (bodies 100). In alternative embodiments, such conical structure may taper in the direction of a radiation exit window 211 of the optical element (i.e. in a direction away of the second face 142 of the light transmissive body 100 (bodies 100). Note that only by way of example the optical element 24 is drawn in combination with the element comprising the core-shell(s) configuration. The optical element may especially be used in combination with essentially any of the herein described elements 5.

(66) In FIG. 4b, the light transmissive body 100 is solid.

(67) FIGS. 4a and 4b especially show embodiments of the luminescent element 5 comprising a plurality of elongated light transmissive bodies 100, each elongated light transmissive body 100 comprising 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. Further, the elongated light transmissive bodies 100 differ in one or more of a length L of the elongated light transmissive bodies 100, b type of luminescent material 120, c concentration of luminescent material 120, d concentration distribution over the elongated light transmissive body 100, and e host matrix for the luminescent material 120. As shown, each elongated light transmissive body 100 has an axis of elongation BA, which are here coinciding. Further, one or more of the elongated light transmissive bodies 100 comprise cavities 1150. In FIG. 4a, the smallest elongated body 100, indicated with reference 100 is massive, whereas in FIG. 4b the smallest elongated body 100 also includes a cavity 1150, indicated with reference 1150. The notationsrefer to the inner elongated body 100 and the notations refer to the outer elongated body 100. Note that in principle more than two elongated bodies 100 may be applied. As shown, the elongated light transmissive bodies 100 are configured in a core-shell configuration wherein a smaller elongated light transmissive body 100 is at least partly configured in the cavity 1150 of a larger elongated light transmissive body 100 and wherein the axes of elongations BA are configured parallel. The side faces 140 of adjacent elongated light transmissive bodies 100 have no physical contact or only over at maximum 10% of their respective surface areas.

(68) FIGS. 4a-4b also show embodiments of the lighting device 1 comprising:

(69) a light source 10 configured to provide light source light 11;

(70) the luminescent element 5 according to any one of the preceding claims, wherein the elongated light transmissive body 100 comprises a radiation input face 111 and a first radiation exit window 112; wherein the luminescent material 120 is configured to convert at least part of light source light 11 received at the radiation input face 111 into luminescent material radiation 8, and the luminescent element 5 configured to couple at least part of the luminescent material radiation 8 out at the first radiation exit window 112 as converter radiation 101.

(71) Each 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 side face 140 comprises the radiation input face 111, wherein the second face 142 comprises the radiation exit window 112. The different lengths are indicated with L and L, respectively, though here the lengths are essentially identical.

(72) One or more light sources 10 are configured to provide light source light to the side face 140 of an outer elongated light transmissive body 100 and/or wherein one or more light sources 10 are configured to provide light source light 11 to one or more first faces 141, wherein the one or more first faces 141 are end faces, and/or wherein one or more light sources 10 are configured in a cavity 1150 of an inner elongated light transmissive body 100 and configured to provide light source light 11 to the side face of the inner elongated light transmissive body 100. In specific embodiments, in a first mode of operation the lighting device 1 is configured to provide white light. In other specific embodiments, the lighting device comprises a first mode of operation wherein colored light is provided. In yet further embodiments, the lighting device 1 may further comprise a control system, configured to control the light sources, where the different light transmissive bodies 100 are configured to provide luminescent material light with different spectral distributions. In such embodiments, the spectral distribution of the lighting device light 101 may be tunable.

(73) The optical element 24 comprises in the schematically depicted embodiment a radiation entrance window 211 and a radiation exit window 212, and essentially consists of light transmissive material.

(74) Embodiments of tapered rods are shown in FIG. 5a-5b. In FIG. 5b, the cross-sectional area may essentially stay constant. Hence, these figures schematically depict embodiments wherein the elongated light transmissive body (100) tapers along at least part of the length of the axis of elongation (BA). Or, the elongated light transmissive body (100) tapers along at least part of its length L. FIG. 5b schematically depicts an embodiment wherein the tubular elongated light transmissive body (100) tapers along at least part of the length of the axes of elongation (BA) while maintaining a cross-sectional area perpendicular to the axes of elongation (BA) constant, see the dashed lines in the tapered section. Normally, if the area is becoming smaller, light could be extracted or the light is reversed back to the nose.

(75) Because we can make use of recycling of the light, it appeared possible to make area of the entrance of the optical component, such as a CPC, even smaller than area of cross section of the hollow rod. Part of the light may thus be recycled at the second face. This embodiment is not depicted.

(76) A luminescent concentrating body with a specific cross-sectional shape that enables improved coupling efficiency, improved light extraction, improved cooling, improved converter mounting, improved module assembly, and/or improved light source robustness by features related to that specific cross-sectional shape, is hereinamongst othersproposed.

(77) In embodiments, one or more features may include: embedding of the pump LEDs within linear cavity in the converter; positioning/alignment of the converter body in the high brightness module; defining the distance from pump LEDs to the converter; reducing the light extraction cones from 4 down to 2 resulting in reduced light losses and therefore an increase module performance; mounting of multiple converters next to each other or within each other, enabling spectral tuning of the light source output; specific converter cross sectional profiles that enable one or more distinct advantages are I shapes, O shapes, T shapes, U shapes, and more complex versions.

(78) In embodiments (I) a highest linear optical flux density for irradiation with LEDs of a luminescent light concentrator, which is needed to keep the light source dimensions limited and the cost lowest, can be generated by applying chip scale package LEDs (CSP-LEDs). However, contrary to the thin film flip chip LEDs that are used in for example the first generation HLD product, and which are top-emitters (i.e., only emitting from the top surface), all currently available CSP LEDs are 5-side emitters, resulting in higher light losses as it is difficult to couple the light that is emitted sidewards from the chips into the conversion rod. Modeling shows a light loss of ca 10% even with a rectangular luminescent converter that has a width that is significantly larger than the width of a CSP LED. By shaping the luminescent converters such that they surround the pump LEDs, the coupling efficiency can be significantly improved, as in this way almost all light can be captured by the conversion rod.

(79) FIG. 6a schematically shows an embodiment of an I-shaped luminescent conversion rod for maximum coupling efficiency of pump light. Left, a cross sectional view of I-shaped conversion rod clamped between two rod holders, sandwiched between two PCB's each having a linear array of 5-side emitting CSP-LEDs is shown. In the middle a 3D perspective view of the conversion rod is shown, and at the right, a variant of light source with ceramic substrates on heat spreaders is shown.

(80) Reference 17 refers to and PCB, such as an MCPCB, which is a metal-core PCB (printed circuit board. Reference 18 refers to rod holder or elongated light transmissive body hold, of which e.g. a top rod holder and a bottom rod holder may be available. However, other configurations may also be possible. Reference 1150 indicates a cavity.

(81) In embodiments (II), the distance from pump LEDs to the rod is controlled by the depth of the groove in the rod that comprises the stack of dies and solder; currently this is handled by a separate mechanical provision in the rod holders making these components complex and expensive. In this embodiment, the rod is simply placed directly between the two opposing PCB's, ideally having substantially the same width as the rod holder that is rigidly mounted to at least one of the PCBs. In other embodiments both rod holders have the same thickness and are just mounted and fixated in place, enabled by the easy placement of the rod; in this case no movable top rod holder is needed anymore that in the first generation product still needs to be clamped to the rod. Alternative board configurations including ceramic boards are possible as well.

(82) FIG. 6b schematically depicts a cross sectional view of light source with I-shaped conversion rod where the gap between the top face of the pump LEDs and the rod is determined by the groove in the rod. Here, the rod has substantially the same width as the rod holders, where both rod holders are mounted fixed to the boards/heat spreaders.

(83) In embodiments (III) the light conversion is realized by a longitudinally tiled rod, enabling spectral broadening of the overall output by using different compositions of the two U-shaped rods. An additional feature is realized by independent addressing of the pump LEDs on the two boards, which enables dynamic tuning of the overall output spectrum.

(84) FIG. 6c schematically depicts a schematic cross-sectional view of two light source embodiments according to the invention comprising two U-shaped conversion rods forming together an I-shaped conversion body. The pump LEDs on the two opposite boards may be driven independently, enabling temporal variation of the overall output spectrum.

(85) In embodiments (IV) In addition to the tiling of the conversion body, in further embodiments of the light source the rod holders are longitudinally tiled for ease of assembly: in this way the two halves of the light source can be assembled independently and subsequently be mounted together, e.g. by clamping the corresponding rod holders of the two halves to each other, or by using dedicated spacers between the boards. Light extraction optics may be mounted after having assembled the rods in their holders and the two halves have been mounted together. By using split rod holders, soldering of rod holders directly to both PCB's (or to the ceramic substrate if used) is enabled.

(86) FIG. 6d shows a schematic cross-sectional view of a light source embodiment according to the invention comprising two U-shaped conversion rods forming together an I-shaped conversion body, and where also the rod holders are tiled: the module comprises two halves that are separately assembled and afterwards bolted or clamped together. Left, the corresponding rod holders of both half-modules are clamped together upon assembly of the complete module, and right, the rod holders are soldered (or glued) to the respective boards. Using distance pieces, the two half-assemblies are mounted together at the desired distance from each other.

(87) Reference 19 refers to a distance element or distance piece. This may be a piece of metal or ceramic material or polymeric material. Especially, the distance element may be a temperature resistant material. In embodiments, the distance element 19 may be a glass or a ceramic material. In further embodiments, the distance element 19 may be a liquid crystal polymer.

(88) In embodiments (V) the distance from pump LEDs to the rod is controlled by an alignment feature in the circumference of the rod that coincides with a feature in the mechanics around the rod. This alignment feature can either be one or more (longitudinal) grooves in the rod, or it can be (longitudinal) protrusions from the rod.

(89) FIG. 6e schematically depicts a schematic cross-sectional view of light source with conversion rod comprising longitudinal features for alignment of the lateral rod position, and optionally grooves for embedding the pump LEDs. On the left, a rod with LED-embedding grooves and rod-alignment grooves is depicted, and on the right, a rod with alignment protrusions is schematically depicted.

(90) Reference 1160 indicates a protrusion.

(91) In embodiments (VI), a tube-shaped luminescent converter is applied. The hollow center part of this converter may be substantially filled by a second luminescent converter rod that may have a different composition than that of the tube-shaped converter. FIG. 6f schematically depict a non-limiting number of embodiments. It schematically shows cross sectional view of the core of the light source comprising a hollow conversion tube. Pump LEDs as mounted parallel to the tube and potential irradiating laser diodes irradiating one of the facets of the center body, as well as the cooling blocks for cooling the luminescent converters have been omitted for simplicity.

(92) In an embodiment a tubular converter is applied with a wall thickness significantly smaller than half the outer diameter of the tube. The cross-sectional shape may be circular or oval, and/or may have flat sides for maximum coupling of pump light from the LEDs into the converter. The thinner the wall, the smaller the extinction losses as the 4 escape cones of converted light that are associated with the 4 sides of a square or rectangular rod are reduced to only 2 escape cones (this is the limit for an infinitely thin wall; note however that the thickness in combination with activator concentration should be large enough to enable substantial conversion for practically achievable activator concentrations in the converter material).

(93) In a further embodiment, a substantially transparent and highly translucent rod is positioned inside the luminescent conversion tube, providing independent light guidance in the longitudinal direction of both bodies. The outer rod is pumped by blue LEDs mounted parallel to the rod, while the inner rod acts as a light guide and homogenizer for blue and/or red laser diode light that is coupled into the rod at one end, where the tube is provided with a mirror to reflect part of the converted light (emitted towards this end facet). The center rod may be shaped to optimally fill the center cavity, or preferably has a polygonal cross-sectional shape for improved spatial homogenization. Some, preferably forward, scattering may be present in the center rod and/or on the outer surface of the rod to improve the homogeneity of the light at the exit facet.

(94) In an alternative embodiment, a luminescent conversion rod is mounted within the hollow luminescent conversion tube, the rod and the tube having different luminescent emission spectra. For maximum converted light guidance performance, the center rod preferably has an absorption length much smaller than its diameter, or has a substantial square or rectangular shape to prevent the occurrence of more than 4 escape cones in the cross sectional plane.

(95) FIG. 6g schematically depicts some non-limiting examples of bodies in cross-sectional views, with massive bodies 100 and with hollow bodies 100 having cavities 1150. Would variants I or III be tapering along the length of the body 100 (i.e. perpendicular to the plane of drawing, a (truncated) pyramid may be obtained. Would variants II or IV be tapering along the length of the body axis BA, then a (truncated) hexagonal pyramid may be obtained. Would variants III or VI be tapering along the length of the body axis BA, then a (truncated) cone may be obtained (see e.g. FIG. 5b).

(96) FIG. 6g amongst others depicts a body 100 with a hexagonal cross-section. Also octagonal cross-sections may be applied. The number of side faces (in cross-section) may be defined a n, with n being 4 for square or rectangular, and being 6 for hexagonal, and in effect being unlimited for a round cross-section. In embodiments, n is selected from the range of 4-50, such as 6-50, like 6-40. In other embodiments, the body is round (right part of the drawing).

(97) In embodiments, wherein a cylindrical light converter is applied, an efficient light extracting collimator can be applied that results in a homogeneous light emitting surface without a center hole and without significant tendue increase, by applying a circular version of a 2-dimensional CPC (or an optimized shape close to that). FIG. 7a schematically shows a cross sectional view and a front view, with a schematic longitudinal cross-sectional view (left) and front view (right) of the core of the light source comprising a hollow conversion tube with a light extracting collimator that fills the center gap of the tube. Pump LEDs as well as cooling provisions, which are mounted parallel to the tube, have been omitted for simplicity.

(98) FIG. 7a schematically depicts an embodiment wherein the optical element 24 comprises a first wall 1241 and a second wall 1242 surrounding the first wall 1241 thereby defining an optical element 24 having a ring-like cross-section, wherein the optical element 24 comprises a radiation entrance window 211 and a radiation exit window 212, wherein the radiation entrance window 211 is optically coupled with a plurality of elongated light transmissive bodies 100. Note that the same cross-sectional views may apply to a hollow elongated light transmissive body 100 (including a cavity) optically coupled to such optical element 24. The optical element may be hollow or may be a massive body comprising light transparent material.

(99) In case of a combination of multiple light converter bodies, a light extracting optical component such as a solid CPC, a solid truncated pyramid or a solid truncated cone, is preferably mounted to the bodies after the latter ones have been mounted and fixed in position. In those cases where they are not completely fixed, i.e., can move somewhat, relative to each other, the light extractor may be mounted rigidly to only one of the converter bodies, e.g. the outer tube, while the inner rod is preferably brought in optical contact with the light extracting optics via a flexible gel.

(100) In case of a combination of a light converting tube with a non-converting center rod, the light extracting optical component needs to be mounted only to the luminescent converter body (as transmission through the center rod is high even without optical contact).

(101) FIG. 7b schematically depict a non-limiting number of optical elements. Here, especially concentrators are depicted. FIG. 7b schematically depicts a revolved CPC (I), a crossed CPC (II), a compound CPC (III), a lens-walled CPC (IV), a crossed V-trough concentrator (V), a polygonal CPC (VI), a square elliptical hyperboloid (SEH)(VII), a V-trough (VIII), a compound parabolic concentrator (IX), a compound elliptical concentrator (X), and a compound hyperbolic concentrator. Further options or hybrids between two or more of these may also be possible.

(102) However, also a dome shaped optical element may be applied, see FIGS. 7c (and 4b), embodiment I.

(103) Optical elements may e.g. increase in diameter with increasing distance from the transmissive body, such as shown in most of the drawings, expect for the half sphere or dome in FIG. 7c, embodiment I. However, also e.g. conical structures or 1-dimensionally tapered elements, where especially a characteristic width (or diameter) decreases with increasing distance from the transmissive body could be relevant. In such embodiments, light extraction is to the side(s) of the element (at grazing angles).

(104) Alternatively, an optical element 24 with decreasing outer dimensions for increasing distance from the entrance plane can be applied (II). This may create a collimated extracted beam, in contrast to the non-collimated beam that is emitted from a dome-shaped optical element (I). Alternatively, a wedge-shaped structure may be applied (not depicted).

(105) FIG. 7a schematically depicts a revolved optical element, such as a revolved CPC. Alternatively, a number of small optical elements may be chosen or a plurality of fibers may be chosen (not shown), which are optically coupled to the (hollow) light transmissive body 100. FIG. 7d schematically depicts an embodiment wherein a plurality of optical elements 24 are applied, downstream of the radiation exit window 112.

(106) In embodiments, in case of a shaped converter body that is different from the desired light emitting surface shape, or a combination of multiple light converter bodies, a further light mixing portion of the converter structure may be used that spatially homogenizes the light before being further extracted (and possibly pre-collimated) by the extraction optics. In other words, a mixing portion is provided between the converter body and the beam shaping and light extracting optics.

(107) With the new multi-component manufacturing approaches, concentrator shapes and compositions as presented in this document, most or all of these disadvantages may be overcome or may be significantly reduced, resulting in high brightness light sources with significantly reduced cost and with highly improved performance characteristics.

(108) A monolithic luminescent concentrating body is proposed that has a refractive index that is constant throughout that body, while the optical absorption and/or the emission spectrum is a function of location in that body. In particular, a luminescent converter is proposed that has a high optical absorption for pump light in an outer layer of the body while the inner part of the body has a lower absorption for the pump light, preferably is transparent for the pump light. This can be realized by 2-k extrusion, by co-injection molding (first mold the core of the body, and use that as an insert for the molding of the outer shell of the body), by subsequent gel casting (same principle), or by subsequent pressing (same principle). Upon sintering of these bodies, a luminescent converter results with the requested properties. In a second application, the light extractor body is co-created with the luminescent converter body in the green phase by 2-k injection molding, pressing, 2-k pressing, or 2-k gel casting, based on two materials that have different spectral absorption characteristics while having the same refractive index. In all cases, the crystal structures of the 2 (or more) materials are chosen to be very similar to enable successful sintering, to preserve a cubic lattice throughout the whole body, and prevent second phase formation. This is realized by using host materials that are very similar, e.g. substantially the same garnet composition, but with a different doping level of the Ce activator, or with little deviations in the lattice. Some (small) differences in the garnet host material may also be tolerated, but preferably these are substantially equal.

(109) The term 2k refers to two components. It may also refer to multi-component, as the principle of two components may in general also be applied for more than two components.

(110) Pressing, such as especially uni-axial pressing, may be applied as well. Pressing may include dry powder pressing or wet suspension pressing. Further, a mold may be used when pressing.

(111) In embodiments, a monolithic converter comprising an outer layer with high absorption of pump light and inner part with low absorption of pump light is proposed. In embodiments a rod or bar is realized with absorption of pump light in an outer layer and lower absorption of pump light in the inner part. The rod or bar has a refractive index that is constant and a crystal structure that is substantially homogeneous throughout the converter as well. This is realized by 2-component extrusion, by injection molding of a shell layer around a (molded or extruded) core, or by casting of a shell layer around a casted (or maybe even molded/extruded) core, after which the composed body is sintered, see FIG. 8a, which shows a monolithic poly-crystalline ceramic bar or rod with luminescent outer layer, indicated with reference 120 (luminescent material), and non-luminescent inner part 107; both parts have the same refractive index and coefficient of thermal expansion, but different spectral absorption characteristics. Both a rectangular and a circular variant are depicted.

(112) Many other shapes can be realized as well, including polygonal transverse cross-sectional shapes, oval shapes, and (partial) combinations of such. It may have flat sides for maximum coupling of pump light from the LEDs into the converter.

(113) In embodiments within this class of configurations, a cylindrical, oval, or polygonal (transverse cross-sectional shape) converter (or some combination thereof) is applied with a pump-light absorbing wall thickness significantly smaller than half the outer diameter of the rod. The thinner the wall, the smaller the extinction losses as the 4 escape cones of converted light that are associated with the 4 sides of a square or rectangular rod are reduced down to only 2 escape cones for a very thin pump-light absorbing circular shell.

(114) In alternative embodiments, the center body of the luminescent conversion bar/rod has a different luminescent emission spectrum than the shell of the body. For maximum converted light guidance performance, the center rod preferably has an absorption length much smaller than a characteristic diameter, while also the thickness of the outer layer is small compared to a characteristic diameter of the bar/rod. See FIG. 8b, which shows a monolithic poly-crystal ceramic bar or rod comprising a luminescent outer layer and a luminescent inner part; both parts have substantially the same refractive index and coefficient of thermal expansion, but different emission spectra by differences in host composition and/or activator concentration. Both a rectangular and a circular variant are depicted. The different luminescent materials 120 are indicated with references 120 (shell) and 120 (core).

(115) In embodiments, a monolithic poly-ceramic luminescent converter body with light extractor is proposed. For increasing light extraction a light extractor is applied to the luminescent converter bar/rod; this may be a collimating type of extractor, e.g. with an outer shape as that of a compound parabolic concentrator (CPC), or a dome type of extractor. Typically the light extractor and the luminescent converter body are connected by an intermediate (optically transparent) medium with a refractive index somewhere in between the refractive indices of the components. Some variants are displayed in FIG. 8c, which shows a monolithic polycrystalline ceramic body with luminescent outer shell and a non-luminescent core (i.e., with a core that does not absorb the pump light), to which a light extractor is glued (top) (see also FIGS. 8a-8b). Alternatively, the center part of the poly-crystal body is also luminescent, but emitting a different spectrum as the outer shell (bottom) (see also FIGS. 8a-8b). Cross sectional shapes of the bar/rod and of the light extractor may vary; depicted are rectangular (left of the two right figures) and round shapes (right of the two right figures). The optical element, here e.g. a massive light extractor, is indicated with reference 24.

(116) In specific configurations, a rectangular light extractor is combined with a round luminescent converter, combining the preferred light exit window for a projection system with the preferred round luminescent converter shape for maximum (light extraction) efficiency; see FIG. 8d, which shows a combination of a circular luminescent converter body with a rectangular light extractor to match a preferred spatial extent of the light source for specific projection applications.

(117) In embodiments, a monolithic poly-crystalline luminescent concentrator comprising a poly-crystalline converter body sintered together with a poly-crystalline light extractor is proposed. For maximum light extraction as well a maximum robustness the light extractor is made of a poly-crystal ceramic as well as the luminescent converter bar/rod, and these are co-sintered into a single monolithic light concentrator. The match in refractive index of the light extractor with the luminescent converter bar/rod without any other material in between enables maximum light extraction, while the co-sintering also results in an extremely strong component. Tuning of the composition(s) of the converter bar/rod and the light extractor is important to achieve a scatter-free sintered interconnect. See FIG. 8e for some graphical representations, wherein some configurations options for a monolithic poly-crystalline luminescent concentrator, comprising a luminescent converter rod/bar co-sintered with a poly-crystalline ceramic light extractor. The whole body has substantially the same refractive index, but localized differences in activator concentration or in host composition of the garnet material are included by design. The optical element 24 may e.g. have a rectangular cross-section (left of the three right figures), circular (middle of the three right figures), and rectangular (right of the three right figures); the body 100 may e.g. have a rectangular cross-section (left of the three right figures), circular (middle of the three right figures), and circular (right of the three right figures).

(118) For ease of manufacturing, in particular polishing, a conical or double wedge shaped light extractor may be applied rather than a CPC-shaped extractor. Although there will be some increase of tendueendue, and therefor reduction of radiance at the exit window, the advantages of a simpler and cheaper surface finish process may be dominating.

(119) In embodiments, a monolithic poly-crystalline luminescent concentrator comprising a poly-crystalline converter body sintered together with a poly-crystalline light mixing extension is proposed. For homogenization of the spatial light distribution it can be advantageous to use an extension of the luminescent conversion body as a homogenizing light pipe before extracting and projecting the light. In a preferred configuration this extension is realized by co-sintering of a poly-crystalline ceramic extension of the converter with the luminescent converter. In a preferred class of embodiments this is further extended with a co-sintered light extractor. See FIG. 8f for some graphical representations of these embodiments, wherein monolithic poly-crystalline luminescent converter with co-sintered poly-crystalline homogenization section as extension of the luminescent converter rod/bar (top) and with additionally a co-sintered poly-crystalline light extractor (bottom) are displayed. Reference 113 indicates a homogenization or mixing element, configured to mix the luminescent light. Here, the second face or radiation exit window of the light transmissive body can be seen as the part where the light transmissive body changes into the optical element. Likewise, this may apply to the radiation entrance window 211. The radiation exit window 212 has in fact become effectively the second face or radiation exit window of the assembly of light transmissive body and optical element 24.

(120) The light extractor part may be co-molded, co-casted, or 2-k extruded, or may be molded as a separate individual part that subsequently is co-sintered with the luminescent converter body to form a single monolithic poly-ceramic body. Other combinations of shapes, light absorption distributions, and spatial distributions of emission spectra are possible using the various options for components as presented before.

(121) In embodiments, a monolithic poly-crystalline 3-D shaped luminescent concentrator comprising a 3-D shaped poly-crystalline converter body sintered together with a poly-crystalline light extractor is proposed. For minimization of the tendueendue of the light source, or for maximizing light coupling into the light converter, or for optimizing the spatial extent of the light source for the application, it may be advantageous to let the cross-sectional dimensions of the luminescent converter/light pipe change with position (along the optical axis). Obviously this can only be realized by molding, pressing, or casting of the body. Thickness of the outer shell of highly absorbing luminescent material as well as the diameter of the luminescent rod/bar may vary with longitudinal position. Using the approach of a monolithically sintered body as described above, but with varying cross-sectional shapes, enables realization of the highest efficiencies thanks to absence of scattering at the interfaces and a continuous refractive index across the whole component.

(122) The term substantially herein, such as in substantially all light or in substantially consists, will be understood by the person skilled in the art. The term substantially may also include embodiments with entirely, completely, all, etc. Hence, in embodiments the adjective substantially may also be removed. Where applicable, the term substantially 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%.

(123) Where stated that an absorption, a reflection or a transmission should be a certain value or within a range of certain values these values are valid for the intended range of wavelengths. Such, if stated that the transmission of an elongated luminescent light transmissive body is above 99%/cm, that value of 99%/cm is valid for the converted light rays, while it would be clear to the person skilled in the art that the transmission of an elongated luminescent light transmissive body will be well below 99%/cm for the range of wavelengths emitted by the light sources 10, since the source light 11 is intended to excite the phosphor material in the elongated luminescent light transmissive bodies such that all the source light 11 preferably is absorbed by the elongated luminescent light transmissive bodies instead of highly transmitted. As indicated above, the term transmission especially refer to internal transmission.

(124) The light transmissive body is thus especially substantially transmissive for at least (a spectral) part of the converted light, which (also) means substantially non-scattering for at least (a spectral) part of the converted light and showing limited absorption for at least (a spectral) part of the converted light. It may however show a high absorption for other wavelengths, such as especially for at least (a spectral) part of the pump light, or for only (a spectral) part of the converted light. It may also be scattering for other wavelengths than (a substantial (spectral) part of the converted light.

(125) The term plurality refers to two or more.

(126) The term comprise includes also embodiments wherein the term comprises means consists of. The term and/or especially relates to one or more of the items mentioned before and after and/or. For instance, a phrase item 1 and/or item 2 and similar phrases may relate to one or more of item 1 and item 2. The term comprising may in an embodiment refer to consisting of but may in another embodiment also refer to containing at least the defined species and optionally one or more other species.

(127) 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.

(128) The devices herein are amongst others 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 in operation.

(129) It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb to comprise and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. Unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to. The article a or an preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device 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.

(130) Practical designs may be further optimized the person skilled in the art using optical ray trace programs, such particular angles and sizes of microstructures (reflective microstructures or refractive microstructures) may be optimized depending on particular dimensions, compositions and positioning of the one or more elongated light transmissive bodies.

(131) The invention further applies to a device 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.

(132) 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.