REMOTE OPTICAL PUMPING OF LUMINESCENT CONCENTRATION RODS

Abstract

The invention provides a lighting device (1) comprising: 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 light transmissive body (100), the light transmissive body (100) comprising one or more radiation input faces (111) and a radiation exit window (112), wherein the second face (142) comprises said radiation exit window (112); the elongated light transmissive body (100) comprising a luminescent material (120) configured to convert at least part of light source light (11) received at one or more radiation input faces (111) into luminescent material light (8), and the luminescent concentrator (5) configured to couple at least part of the luminescent material light (8) out at the radiation exit window (112) as converter light (101); a light source mirror unit (200) comprising: a plurality of light sources (10) configured to provide said light source light (11) in a direction of a curved mirror (220); said curved mirror (220), configured to collect at least part of said light source light (11) and configured to redirect the collected light source light (11) to at least one of the one or more the radiation input faces (111) of the luminescent concentrator (5)

Claims

1. A lighting device comprising: a luminescent concentrator comprising an elongated light transmissive body having a first face and a second face defining a length of the light transmissive body, the light transmissive body comprising one or more radiation input faces and a radiation exit window wherein the second face comprises said radiation exit window; the elongated light transmissive body comprising a luminescent material configured to convert at least part of light source light received at one or more radiation input faces into luminescent material light, and the luminescent concentrator configured to couple at least part of the luminescent material light out at the radiation exit window as converter light; a light source mirror unit comprising: a plurality of light sources configured to provide said light source light in a direction of a curved mirror; said curved mirror, configured to collect at least part of said light source light and configured to redirect the collected light source light to at least one of the one or more the radiation input faces of the luminescent concentrator; wherein the lighting device comprising a plurality of light source mirror units in the range of two to eight, wherein the elongated light transmissive body comprises two or more side faces, wherein two or more mirror units are configured to provide the light source light of the respective light sources to two or more different side faces, and wherein the curved mirror has an elliptical shape having a first focus and a second focus, wherein the light sources have light emitting surfaces, wherein one or more light emitting surfaces are configured at the first focus and wherein the elongated light transmissive body is configured at the second focus.

2. The lighting device according to claim 1, further comprising a cooling element in thermal contact with the luminescent concentrator.

3. The lighting device according to claim 1, wherein the two or more side faces comprise one or more radiation input faces, wherein the light source unit is configured to provide said light source light to a first part of the two or more side faces, the lighting device further comprising a cooling element in thermal contact with the luminescent concentrator, wherein the cooling element is in thermal contact with a second part of the two or more side faces.

4. The lighting device according to claim 1, wherein the light sources are configured to provide light source light having an optical axis and wherein the optical axes of the light sources are directed to the curved mirror.

5. The lighting device according to claim 1, wherein the light sources are configured to provide light source light having an optical axis, wherein the elongated light transmissive body has a body axis, wherein one or more light sources are configured to provide said light source light with said optical axis perpendicular to the body axis and wherein one or more light sources are configured to provide said light source light with said optical axis having an angle smaller than 90 and equal to or larger than 45.

6. The lighting device according to claim 1, wherein the light sources comprise solid state light sources having light emitting surfaces with downstream thereof collimators for a pre-collimation of the light source light.

7. The lighting device according to claim 1, wherein the elongated light transmissive body comprises an elongated ceramic or elongated crystal body.

8. The lighting device according to claim 1, wherein the elongated light transmissive body is at least partly enclosed by a light transmissive envelope, wherein the lighting device further comprises a cooling element in thermal contact with part of the light transmissive envelope.

9. The lighting device according to claim 1, wherein the curved mirror has a mirror length in the range of 80-120% of the length of the elongated light transmissive body wherein the curved mirror is configured parallel to the elongated light transmissive body.

10. The lighting device according to claim 1, having a mirror configured at the first face configured to reflect light back into the elongated light transmissive body, and having one or more of an optical filter, a wavelength selective mirror, light extraction structures, and a collimator configured at the second face and a second mirror configured at the second face.

11. The lighting device according to claim 10, wherein the two or more side faces comprise one or more radiation input faces, wherein two or more mirror units are configured to provide said light source light to one or more firsts parts of the two or more side faces, the lighting device further comprising a cooling element in thermal contact with the luminescent concentrator, wherein the cooling element is in physical contact with one or more second parts of the two or more side faces.

12. A lighting system configured to provide lighting system light, the lighting system comprising one or more lighting devices according to claim 1.

13. The lighting system according to claim 12, wherein the lighting system comprises a digital projector or a stage lighting system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0087] 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:

[0088] FIGS. 1a-1e schematically depict some aspects of the invention;

[0089] FIGS. 2a-2d schematically depict some aspects;

[0090] FIGS. 3a-3c schematically depict some embodiments;

[0091] FIGS. 4a-4b schematically depict some aspects;

[0092] FIGS. 5a-5b schematically depict some further variants; and

[0093] FIGS. 6a-6b schematically depict some embodiments.

[0094] The schematic drawings are not necessarily on scale.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0095] 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.

[0096] 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 light to an exit surface.

[0097] 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 said 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.

[0098] 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 light 101, such as at least one or more of green and red converter light 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. 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+.

[0099] The light sources may in principle be any type of point 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.

[0100] 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 light 8 (see also FIG. 1e). Light escaping at the light exit window is indicated as converter light 101, and will include luminescent material light 8. Note that due to reabsorption part of the luminescent material light 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.

[0101] 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.

[0102] 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) at another end of the light guide.

[0103] 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. 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 indicated of the edge faces is reference 147). The second variant is a tubular rod, with first and second faces 141 and 142, and a circumferential face 143. Light sources, not shown, may be arranged at one or more positions around the light transmissive body. Such light transmissive body will have a (substantially) circular or round cross-section. The third variant is substantially a combination of the two former variants, with two curved and two flat side faces. 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.

[0104] 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.

[0105] 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.

[0106] 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 (la) 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.

[0107] High brightness light sources are interesting for various applications including spots, stage-lighting, headlamps and digital light projection.

[0108] 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 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 an intensity gain (FIG. 1e).

[0109] 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. Currently the LED modules used for pumping the luminescent rods are in close contact with the rods in order to couple in as much light as possible, as depicted in FIG. 2a. In this concept the air gap g between the individual LED dies and the luminescent rod is kept as small as possible (tens to a few hundred micrometers) in order to couple in as much light into the rod as possible. In a practical implementation, typically 0.3 min distance is used. Putting more LEDs around the luminescent rod in order to increase pumping power is not possible since all available space is occupied in this concept for the given rod size. Reference 300 refers to a cooling element; reference HS indicates a heatsink. Here, a plurality of heatsinks are applied for thermal management of the light source(s) 10 and of the light transmissive body 100.

[0110] In this invention a method for remote pumping of a luminescent concentrator rod is used in embodiments by using the combination of (i) elliptical mirrors and (ii) pre-collimation and pre-tilting of the discrete LED-sources. The main idea about using an elongated elliptical mirror is rather straightforward: when placing a light source (i.e. the LED) into one focal line of an ellipse, the light will be redirected towards the second focal line (i.e. the luminescent rod). When placing an array of LEDs along the first focal line, an elongated focus will be created along the second focal line. This (astigmatic) focusing is illustrated in FIGS. 2b-2c. However, since the elliptical mirror has focusing strength in only one plane (the plane of the ellipse), the direction vector of the light rays out of this focusing plane will be unaltered and may ultimately miss the luminescent rod, as indicated by the two most right-handed light rays in FIG. 2c. Further optical arrangements are suggested that can further optimize the collection efficiency of this elliptical pumping concept for our luminescent rods. F1 and F2 schematically indicate the first and second focus, respectively.

[0111] As schematically shown in FIG. 2b, in embodiments the optical axis of the light source is not directed to the light transmissive body 100 but to curved the mirror, which is indicated with reference 220 (of a mirror unit 200). Hence, the light source 10 is configured to provide the light source light 11 in a direction of the curved mirror 220. Especially, in embodiments herein, at least part of the light source light, such as at least 50%, like at least 80%, such as at least 90%, such as in embodiments (essentially) all light source light is received by the curved mirror 220, and part thereof, after at least one reflection at the curved mirror 220 may reach the light transmissive body 100. Hence, in embodiments at least 50%, like at least 80%, such as at least 90%, such as in embodiments (essentially) all light source light that is received by the light transmissive body 100 is only received after a reflection at the curved mirror 220. Hence, for an essential part of the light source light received at the light transmissive body 100, the curved mirror 220 is in fact configured upstream of the light transmissive body 100 and the light source 10 is configured upstream of the curved mirror 220. Hence, in embodiments the optical axis, indicated with reference O, may not direct to the light transmissive body (but to the curved mirror 220).

[0112] The light transmissive body 100 is especially an elongated light transmissive body.

[0113] Reference 2d schematically depicts a perspective view of an embodiment of the device 1, where with two mirror units 200, each having a length L1, substantially identical to the length L of the light transmissive body 100. The light sources 10 are configured in a row having a length L2, also being substantially identical to the length L of the light transmissive body 100. The light sources 10 are especially configured in the first focus or focal line F1 and the second focus/focal lines F2 may coincide with the light transmissive body 100. Note that the second focus/focal lines F2 do not necessarily coincide at the light transmissive body 100 but may also be configured parallel, e.g. at respective radiation input faces 111. Especially, the (elongated) curved mirror has a mirror length L1 in the range of 80-120% of the length of row of light sources, which length is indicated with reference L2. The mirrors 220 as schematically depicted in FIG. 2d may substantially have the shape of an elliptical cylinder segment (i.e. segment of an elliptical cylinder). Note that each cross section perpendicular to an axis of elongation of the mirror 220 may provide such half ellipse shape.

[0114] Referring to FIG. 2d, at one side a single curved mirror 220 is depicted. In yet other embodiments, such as especially over substantially the same length L1, two or more curved mirrors 220 may be configured (in series). Hence, the term, the light source mirror unit may include a plurality of curved mirrors, such as configured one next to the other to form an elongated mirror (having a substantially the length L1).

[0115] Optionally, also at the second face 142 a mirror 21 may be configured, such as a mirror with a hole 21b such that light may escape through the hole and reflected light may be reflected back in the elongated body. This mirror 21, or these mirrors 21, may not be in physical contact with the second (or first) face, but may be configured close to the second (or first0 face, such as at a distance of 0.1-1 mm, like 0.1-0.5 mm.

[0116] Reference 500 schematically indicates a gas, especially air, displacement unit, configured to provide a flow 501 of gas between the elongated body 100 and the light sources 10 and/or mirrors 220. In this way, a further cooling may be obtained.

[0117] By using multiple elliptical mirrors, a most effective remote optical pumping arrangement can be obtained for the light concentrator device. This may be combined with pre-collimation and pre-tilting of the individual LED outputs (see below). Several arrangements are depicted in FIGS. 3a-3c.

[0118] FIG. 3a shows an arrangement where two elongated half-elliptical mirrors are being used in order to collimate the output of two LED strips emitting in opposite directions. One of the the two focal points of the two half-ellipses coincides with the center of the rod entrance face, whereas the other focal points of the two half-ellipses coincide with the center of the respective LED modules. As a result, the long axes of both half-ellipses may make a certain angle with respect to each other, .sub.ellipse (indicated in the drawing with a), depending on the thickness of the LED module and the intermediate heatsink. Since the angular dependence of the emission of the LEDs is in forward directions (e.g. Lambertian), an optimal .sub.ellipse can be found to maximize the amount of light reaching the rod.

[0119] In principle the whole 2a upper (and lower) half space can be used for collection and focusing of light from the two LED modules. In practice however the luminescent rod needs to be mechanically clamped for positioning and cooling purposes. As a result only part of the 2 upper (and lower) half space will be accepted by the elliptical mirrors, the rest of the light will be lost or scattered into the mirror cavity. This dead angle strongly depends on the ratio between of the long and short axes of the ellipse and can be minimized accordingly. The dead angle would be minimum for very elongated (large eccentricity) ellipses; however, in this case optical aberrations will strongly enlarge the spot at the position of the luminescent rod. An optimum can be found here depending on the LED light output angular distribution, dimensions of the LED-die, rod size and ellipse geometry. In FIG. 3a, the mirror(s) 220 are curved mirrors that may substantially have an elliptical shape, or which curvature substantially follows the curvature of a curved part of an elliptical shape. Here, embodiments are schematically depicted wherein the mirrors may comprise segments of ellipses, especially half-ellipses (half-elliptical mirrors).

[0120] FIG. 3b shows an arrangement with 4 elongated truncated elliptical mirrors. Due to symmetry considerations the amount of light coupled into the luminescent rod is substantially twice the amount obtained by the geometry of FIG. 3a (assuming four instead of two identical LED arrays and assuming no contribution from rays that hit the rod via the other elliptical mirror).

[0121] In FIG. 3c an arrangement is shown with eight elongated truncated elliptical mirrors. Since the above mentioned dead angle is larger in this case, the collection efficiency of each individual ellipse is smaller as in FIGS. 4a and 4b. Although still more light might be coupled into the luminescent rod (since the amount of LED arrays doubles), the expected overall collection efficiency of this arrangement may be smaller than for the arrangements in FIGS. 4a and 4b. Moreover, also the luminescent rod should be mechanically clamped and cooled. In the arrangement of FIG. 3c, there is less room for this.

[0122] A solution may be to apply an air flow inside the arrangement to cool the rod. An inlet may be applied in the assembly and an outlet to direct the airflow inside and outside respectively. The airflow may be originating from a (small) fan, such as the above indicated air displacement unit. In such a configuration the rod may also be supported at a few locations, hanging substantially in free space.

[0123] However, in the various configurations of FIGS. 3a-3c, the rod may be contacted and cooled within the dead zones of the elliptical mirror configurations. This may be done by clamping the rod in between a cooling block, typically a metal shape, for instance made from copper or aluminium. Also, the LED/elliptical mirror configuration in FIGS. 3a-3c may be rotated with respect to the rod at varying angles. In other words, in FIGS. 3a-3c the rod may be rotated at various angles compared to the depicted direction of the rod.

[0124] Hence, FIGS. 3a, 3b, 3c schematically depict embodiments comprising 2, 4 and 8 light source mirror units, respectively.

[0125] Another opportunity to cool the rod when illuminated from all sides is to mold a non-luminescent transparent ceramic cooling envelop (400) around the rod. If the ceramic envelope is molded from a suitable ceramic, such as YAG, the envelope can be made fully transparent without disturbing the optical light path. The cooling envelope has a relatively high thermal conductivity and thus aids to spread out the heat. The envelope may be contacted at various locations that are not within the optical path by non-transparent heat conducting materials, such as copper to allow proper heatsinking. The cooling envelope surfaces may be polished. The extra refractions at the cooling envelope may be taken into account in the design of the optical path. It is required that the cooling envelop may hold and support the rod at some locations but is not in optical contact to the rod in order to maintain light guiding within the rod. Hence, a thin effective airgap is present between the rod and transparent cooling envelope. As such, the shape of the inner surface of the cooling envelope is similar to the shape of the luminescent concentrator but slightly larger. The cross-sectional outer shape of the cooling envelope may deviate and consist of many shapes, for instance rectangular or round. Examples of these embodiments are schematically depicted in FIGS. 4a-4b. The envelope is indicated with reference 400. A small air gap is schematically draw in FIGS. 4a and 4b. note that in FIG. 4a the shape of the envelope 400 is substantially the same as the elongated body 100, whereas in FIG. 4b the shapes are different.

[0126] In order to collect and redirect light as much as possible towards the second focal line, the output from the individual LEDs may be pre-collimated (in the XZ direction) by an additional (cylindrical) optics. As a result the divergence angle of the light beam emitted by the individual LEDs (in the YZ plane) becomes smaller and less light is wasted at the two distant rod edges. This is illustrated in FIG. 5a. The light emitted by the distant LED modules can be even better directed towards the luminescent rod by slightly pre-tilting the LEDs with respect to the long axis of the luminescent rod. This is illustrated in FIG. 5b. This also works without pre-collimation since the angular dependence of the emission of an LED is in forward directions (e.g. Lambertian). The angle between the optical axis O and the body axis BA is indicated with . This angle may be about 90, or smaller, such as down to about 35, such as 45 close the the first face 141 and/or second face 142. The angle is the smallest angle. Note that the angle may be comprised by a triangle defined by a normal P (perpendicular) to the body axis BA and connecitng the light source 10 and the body axis BA, the optical axis O of the light 11 of the same light source 10 and the body axis BA.

[0127] Another way to ensure that the light does not miss the rod, is to provide mirrors at the left and right sides of the rod and LED arrays (see also above).

[0128] Below, some specific embodiments are shown and described. FIG. 6a schematically depicts a configuration with high light output. Side mirrors can be present parallel to the plane of drawing (i.e. parallel to the first face 141 and/or second face 142, respectively (faces 141,142 not indicated in this drawing). FIG. 6b. schematically depicts substantially the same configuration but with 1 LED strip per side. In another variant to FIG. 6b the LED strip consists of side-emitting LEDs directing more light upwards and downwards to interact with the curved mirror.

[0129] For the configuration with 4 LED strips and two (half) ellipses (FIG. 6a) with side mirrors, we first performed ray-trace simulations omitting the clamping blocks. If also the room needed to hold (and cool) the LEDs are omitted, an efficiency of 83% was found, i.e. 83% of the photons emitted by the LEDs reach the luminescent rod. With realistic block dimensions for clamping the LEDs, this number drops to 74%. If also the rod is clamped at the full area of the short side faces (as shown in FIG. 6a), the efficiency is only 62%, since the small sides cannot be used. In this examples the LEDs are not pre-tilted. Moreover, light from the LEDs at the left side can no longer reach the right side of the rod or vice versa.

[0130] It is also possible to use only 1 LED strip at each side (FIG. 6b). Then the best configuration is to direct the emitting side to the rod, resulting in an efficiency of 90%. In FIGS. 6a and 6b, but also in other figures, the mirrors 220 comprise parts of ellipses. However, especially or parts of elliptically shaped elements. Especially, the curved mirrors are configured such, that two foci (especially including two focal lines or two focal faces or two focal volumes) are obtained. Note that in FIG. 6a .sub.ellipse (i.e. ) is substantially equal to zero.

[0131] Hence, the invention may e.g. provide a concentrating light source, consisting of a conversion structure that absorbs light from one or more arrays of LEDs, with a curved mirror around it that focuses the LED light onto the conversion structure. Further, the invention may provide such concentrating light source, where a the cross-section of the curved mirror has a shape consisting of 1 or more ellipses, where both the conversion structure and the LED strips are as close as possible to the focus points of the ellipse(s). Further, the invention may provide such concentrating light source, where the cross-section of the curved mirror has a shape consisting of two ellipses, where both the conversion structure and the LED strips are as close as possible to the focus points of the ellipses. Further, the invention may provide such concentrating light source, containing side mirrors perpendicular to the long sides of the rod and to the LED strips. Especially one of the side mirrors may be configured as end mirror (such as end mirror 21, see amongst others FIGS. 1a, 1b, and 2d). Further, the invention may provide such concentrating light source containing clamping and cooling devices for LEDs and conversion structure. Further, the invention may provide such concentrating light source, where the individual LEDs are tilted such that the amount of LED light arriving at the conversion structure is maximized.

[0132] Applications include but are not limited to projectors, lamps, luminaires, or other lighting systems such as shop lighting systems, home lighting systems, accent lighting systems, spot lighting systems, theater lighting systems, fiber-optics application systems, projection systems, display systems, warning sign systems, medical lighting application systems, indicator sign systems, and decorative lighting systems, portable systems and automotive applications.

[0133] 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%. 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.

[0134] 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.

[0135] 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.

[0136] 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. 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.

[0137] 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.

[0138] 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.