Lighting device with switching material

Abstract

A lighting device comprises a light-emitting module with light-emitting elements, wherein the light-emitting elements are arranged adjacent to each other and are configured to emit light towards a light-emitting side. The light-emitting module is configured such that the light-emitting elements can be addressed partially independently of each other, such that some may be brought into a switched-on state while others are brought into a switched-off state. A top layer is disposed on the light-emitting module at the light-emitting side. Further comprising a switching material capable of a reversible change in transmittance for the light emitted by changing to a higher transmittance in regions where the top layer situated on light-emitting elements in the switched-on state or to a lower transmittance in regions of the top layer situated in the switched-off state. The invention further refers to methods for producing and operating a lighting device and using a lighting device.

Claims

1. A lighting device, comprising: a light-emitting module having independently-addressable adjacent light-emitting elements without a reflective barrier disposed therebetween, the light-emitting elements being configured to emit light towards a light-emitting side; and a top layer disposed on the light-emitting module at the light-emitting side, the top layer comprising a switching material capable of a reversible change in transmittance for the light emitted by the light-emitting elements, the top layer being controllable to individually change to a higher transmittance in regions of the top layer situated on each of light-emitting elements in a switched-on state compared to a transmittance in regions of the top layer situated on each of light-emitting elements in a switched-off state, the switching material having a porous structure that comprises: a non-light absorbing material structure having a plurality of sub-micron pores, and a polymer matrix filling the sub-micron pores, a difference between a refractive index of the non-light absorbing material structure and a refractive index of the polymer matrix changeable with temperature.

2. The lighting device according to claim 1, wherein the regions of the top layer situated on light-emitting elements in the switched-on state have translucent properties.

3. The lighting device according to claim 1, wherein the switching material comprises at least one thermochromic material.

4. The lighting device according to claim 1, wherein the switching material comprises at least one electrochromic material.

5. The lighting device according to claim 1, wherein the top layer is configured to change transmittance by at least 30%.

6. The lighting device according to claim 1, wherein the non-light absorbing material comprises porous silica.

7. The lighting device according to claim 1, wherein the light-emitting module further comprises at least one light-blocking element arranged between the light-emitting elements.

8. The lighting device according to claim 1, wherein the lighting device is disposed in an automotive headlight.

9. The lighting device according to claim 1, wherein the non-light absorbing material structure is formed from a plurality of micron-sized porous silica particles, the plurality of sub-micron pores located within the plurality of micron-sized porous particles.

10. The lighting device according to claim 1, wherein the non-light absorbing material structure forms a mesh slab comprising an interconnected network of the plurality of sub-micron pores and air voids therebetween, a space occupied by the air voids decreasing as the polymer matrix thermally expands, decreasing light scatter, and increasing as the polymer matrix shrinks, increasing light scatter.

11. The lighting device according to claim 1, wherein the switching material comprises magnesium fluoride (MgF.sub.2) scattering elements embedded in a dimethylsilicone matrix material.

12. The lighting device according to claim 3, wherein the at least one thermochromic material is configured to change transmittance at temperatures corresponding to an operating temperature of the light-emitting elements.

13. The lighting device according to claim 3, wherein the at least one thermochromic material comprises at least one material including materials of leuco dye and at least one metal oxide.

14. The lighting device according to claim 3, wherein the at least one thermochromic material comprises at least one leuco dye encapsulated in substantially spherical capsules having an average dimension of about 5 m to about 10 m.

15. The lighting device according to claim 3, wherein the at least one thermochromic material comprises at least one leuco dye disposed on a porous structure.

16. The lighting device according to claim 4, wherein the at least one electrochromic material is configured to change to a higher transmittance when a voltage is applied to the top layer.

17. The lighting device according to claim 4, wherein the at least one electrochromic material comprises at least one material selected from a group of materials comprising metal oxides, metal hydroxides, viologens, conjugated polymers, metal coordination complexes, metal hexacyanometallates, and metal pthalocyanines.

18. The lighting device according to claim 6, wherein the at least one electrochromic material is configured to change to a lower transmittance when a voltage is applied to the top layer.

19. The lighting device according to claim 4, wherein the at least one electrochromic material is configured to change to a lower transmittance when a voltage is applied to the top layer.

20. The lighting device according to claim 9, wherein the plurality of micron-sized porous particles each have a diameter of about 10 mm to about 50 mm and each sub-micron pore has an internal diameter of about 50 nm to about 400 nm.

21. A method for producing a lighting device, the method comprising: providing a light-emitting module by arranging independently-addressable light-emitting elements adjacent to each other without a reflective barrier disposed therebetween such that the light-emitting elements emit light towards a light-emitting side; providing a top layer comprising a switching material capable of a reversible change in transmittance for the light emitted by the light-emitting elements, the switching material having a porous structure that includes a non-light absorbing material structure having a plurality of sub-micron pores, and a polymer matrix filling the sub-micron pores, a difference between a refractive index of the non-light absorbing material structure and a refractive index of the polymer matrix changeable with temperature; and controlling the top layer on the light-emitting module at the light-emitting side to individually change to a higher transmittance in regions of the top layer situated on each of light-emitting elements in a switched-on state compared to a transmittance in regions of the top layer situated on each of light-emitting elements in a switched-off state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will now be described in detail with reference to the accompanying drawing, in which:

(2) FIG. 1 shows a schematic representation of a lighting device from a side view;

(3) FIG. 2 shows a schematic representation of the lighting device of FIG. 1 from a top view;

(4) FIG. 3 shows a schematic representation of a first embodiment of a lighting device according to the invention from a side view;

(5) FIG. 4 shows a schematic representation of the first of embodiment of the lighting device from a top view;

(6) FIG. 5 shows a schematic representation of the first of embodiment of the lighting device with a different state of the light-emitting elements from a side view; and

(7) FIG. 6 shows a schematic representation of the first of embodiment of the lighting device with a different state of the light-emitting elements from a top view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) FIG. 1 shows a schematic representation of a lighting device 2 from a side view. LEDs 4a-4c are arranged adjacent to each other on a substrate 6 and are configured to emit light towards a light-emitting side 8. The lighting device 2 is also shown in FIG. 2 from a top view. The LEDs 4a-4c are forming a segmented LED module and can be addressed independently of each other in that some of the LEDs 4a-4c may be brought into a switched-on state while other LEDs 4a-4c are brought into a switched-off state. In FIGS. 1 and 2, LED 4b is in the switched-on state and emits light as indicated by the arrows 10, while LEDs 4a and 4c are in the switched-off state and inactive.

(9) The LEDs 4a-4c are affected by lateral light diffusion, as light emitted by the LEDs 4a-4c is not only emitted towards the light emitting side 8, but may also be laterally emitted, reflected and/or scattered away from the light-emitting side 8. As the LEDs 4a-4c are arranged adjacent to each other, light may leak from active segments to inactive segments. As a consequence, light 10 appears not only as being emitted from the LED 4b in the switched-on state. Also parts of the inactive LEDs 4a and 4c appear illuminated with light 12. Therefore, a light cross talk or color over between the LEDs 4a-4c occurs, reducing the contrast of the lighting device 2.

(10) FIG. 3 shows a schematic representation of a lighting device 14 according to the invention from a side view. FIG. 4 shows the corresponding top view. A light-emitting module with light-emitting elements 16a-16c and a substrate 18 is provided. The light-emitting elements 16a-16c are arranged adjacent to each other on the substrate 18, such that the light-emitting elements 16a-16c are configured to emit light towards a light-emitting side 20. The light-emitting module is configured such that the light-emitting elements 16a-16c can be addressed independently of each other in that some of the light-emitting elements 16a-16c may be brought into a switched-on state while other light-emitting elements 16a-16c may be brought into a switched-off state. For example, each light-emitting element 16a-16c has electrical connection elements (not shown) that allow for an independent supply with electrical energy and therefore an independent activation of the light-emitting elements 16a-16c. The light-emitting elements 16a-16c may comprise LEDs and/or LED packages. The light-emitting module may therefore represent a segmented LED module in that segments of LEDs may be addressed independently. In FIGS. 3 and 4, light-emitting element 16b is in the switched-on state and emits light as indicated by the arrows 22, while light-emitting elements 16a and 16c are in the switched-off state and are inactive.

(11) A top layer 24 is disposed on the light-emitting module at the light-emitting side 20, wherein the top layer 24 comprises a switching material capable of a reversible change in transmittance for the light emitted by the light-emitting elements 16a-16c. As described above in conjunction with FIGS. 1 and 2, lateral light diffusion occurs and light emitted by the light-emitting element 16b is not only emitted towards the light emitting side 20, but is also emitted laterally, reflected, and/or scattered away from the light-emitting side 20. Light may therefore leak to the inactive light-emitting elements 16a, 16c and parts of the inactive light-emitting elements 16a, 16c would appear illuminated with light 26. As the top layer 24 is configured to change to a higher transmittance in a region 28b of the top layer situated on light-emitting element 16b in the switched-on state compared to a transmittance in regions 28a, 28c of the top layer situated on the light-emitting elements 16a, 16c in the switched-off state, the light 26 originating from the lateral light diffusion of the light-emitting element 16b is at least partially blocked at the regions 28a, 28c of the top layer with a lower transmittance. In particular, a substantial part of the light 26 may be scattered and/or absorbed at the regions 28a, 28c of the top layer 24, while a substantial part of the light 22 may be transmitted through the region 28b of the top layer 24. In particular, the region 28b of the top layer 24 situated on light-emitting element 16b in the switched-on state has translucent properties.

(12) The switching material is capable of a reversible change in transmittance, such that the transmittance of the regions 28a-28c of the top layer 24 may be changed or switched according to the choice of light-emitting elements 16a-16c being active. FIGS. 5 and 6 show a side view and top view, respectively, of the lighting device 16 with light-emitting elements 16a, 16c in the switched-on state and light-emitting element 16b in the switched-off state. Accordingly, the top layer 24 changes to a higher transmittance in the regions 28a, 28c of the top layer situated on light-emitting elements 16a, 16c in the switched-on state compared to a transmittance in region 28b of the top layer situated on light-emitting element 28b in the switched-off state.

(13) The switching material may in particular comprise at least one thermochromic material such as at least one leuco dye and/or at least one metal oxide capable of changing the transmittance with temperature. The at least one thermochromic material may be configured to change transmittance at temperatures corresponding to an operating temperature of the light-emitting elements 16a-16c such that the waste heat produced by the light-emitting elements 16a-16c, and in particular white LEDs with phosphor as wavelength conversion element is sufficient to induce the change in transmittance. The switching material is in particular encapsulated. Encapsulated leuco dyes may for instance be integrated into the top layer 24 or provided as a coating on the top layer 24.

(14) As an alternative or in addition, the switching material may comprise at least one electrochromic material, such as metal oxides, metal hydroxides, viologens, conjugated polymers, metal coordination complexes, metal hexacyanometallates, and/or metal pthalocyanines. The at least one electrochromic material may be configured to change to a higher or a lower transmittance when a voltage is applied to the top layer 24. Voltage can be applied to the regions 28a-28c of the top layer 24 to induce the change in transmittance.

(15) The light-emitting module may further comprise at least one light-blocking element such as a reflective element arranged between the light-emitting elements 16a-16c to provide additional contrast.

(16) The lighting 14 may be configured as adaptive camera flash light, for instance in the field of photography, or as automotive lighting and in particular as an automotive headlight.