Color control for luminescent light guide

1. A lighting device comprising:

a plurality of light sources configured to provide light source light, the plurality of light sources comprising at least a first light source configured to generate first light source light and a second light source configured to generate second light source light;

a light guide comprising a luminescent material, a light exit window, and a plurality of light incoupling areas, the luminescent material configured to be excitable by the light source light, to provide luminescent material light and to reabsorb at least part of the luminescent material light, the light exit window configured for escape of the luminescent material light from the light guide to produce lighting device light, the plurality of light incoupling areas arranged perpendicular to the light exit window and comprising at least a first light incoupling area configured at a first distance from the light exit window, and a second light incoupling area configured at a second distance from the light exit window, the first distance being unequal to the second distance, the first light source is configured to provide the first light source light to the first light incoupling area, and the second light source is configured to provide the second light source light to the second light incoupling area; and

a control unit arranged for controlling a color temperature of the lighting device light by independently controlling the plurality of light sources dependent on a distance each light source is from the light exit window.

2. The lighting device according to claim 1 , wherein the light guide further comprises a plurality of faces, wherein at least part of a first face is configured as the first light incoupling area and the second light incoupling area, and wherein at least part of a second face is configured as the light exit window.

3. The lighting device according to claim 1 , wherein the control unit is further arranged to select which light source from the plurality of slight sources to switch on and to adjust a relative intensity of the plurality of light sources dependent on the distance each light source is from the light exit window.

4. The lighting device according to claim 1 further comprising a plurality of light exit windows arranged perpendicular to the plurality of light incoupling areas.

5. The lighting device according to claim 1 , wherein the plurality of light sources are at least 3 in number, and wherein each distance of the plurality of light incoupling areas to the light exit window are different.

6. The lighting device according to claim 2 , wherein the plurality of light sources comprises two or more subsets each comprising one or more light sources, wherein each subset of light sources is configured to provide light source light to a different face from the plurality of faces of the light guide.

7. The lighting device according to claim 1 , wherein the light guide comprises a light guide material wherein the luminescent material is embedded.

8. The lighting device according to claim 7 , wherein the light guide material comprises a polymeric material.

9. The lighting device according to claim 7 , wherein the light guide material comprises an inorganic material or a hybrid material having both inorganic and organic character.

10. The lighting device according to claim 7 , wherein the light guide material comprises a ceramic material.

11. The lighting device according to claim 1 , wherein the luminescent material comprises an organic dye, quantum dots, and/or a luminescent ion based luminescent material.

12. The lighting device according to claim 1 , wherein the luminescent material has an emission spectrum and an excitation spectrum having spectral overlap, wherein the normalized spectral overlap is greater than 0.02 and less than or equal to 0.5.

13. The lighting device according to claim 1 , wherein the light source light of the plurality of light sources have spectral overlap.

14. The lighting device according to claim 1 , wherein the first distance is larger than the second distance, and the first light source is arranged to produce a red-shifted spectral distribution with respect to light generated by the second light source.

15. A method of controlling a lighting device, the method comprising:

providing light source light from a plurality of light sources, the plurality of light sources comprising at least a first light source generating first light source light and a second light source generating second light source light;

exciting a luminescent material in a light guide with the light source light, the light guide further comprising a light exit window and a plurality of light incoupling areas, the plurality of light incoupling areas arranged perpendicular to the light exit window and comprising at least a first light incoupling area configured at a first distance from the light exit window, and a second light incoupling area configured at a second distance from the light exit window, the first distance being unequal to the second distance, wherein the first light source provides the first light source light to the first light incoupling area, and the second light source provides the second light source light to the second light incoupling area;

providing, by the luminescent material excited by the light source light, luminescent material light;

reabsorbing, by the luminescent material, least part of the luminescent material light;

providing lighting device light from the luminescent material light escaping from the light exit window; and

controlling a color temperature of the lighting device light by independently controlling the plurality of light sources dependent on a distance each light source is from the light exit window.

16. The lighting device according to claim 1 further comprising a radiation input face, the radiation input face comprising the plurality of light incoupling areas, wherein the light exit window has a radiation exit face area, and the radiation input face has a radiation input face area, and wherein the radiation input face area is at least five times larger than the radiation exit face area.

17. The lighting device according to claim 1 , wherein the lighting device light comprises at least part of the light source light in addition to the luminescent material light.

18. The lighting device according to claim 1 further comprising:

a further light source light configured to provide further light source light, wherein the further light source light has no interaction with the light guide; and

a diffuser in paths of the further light source light and the lighting device light.

19. The lighting device according to claim 1 , wherein the plurality of light sources comprises a plurality of light emitting diode light sources.