Display illumination device with a film-based lightguide having stacked incident surfaces
A reflective display includes a reflective spatial light modulator and a frontlight. The frontlight includes a lightguide formed from a film. The lightguide includes an array of coupling lightguides continuous with a lightguide region of the lightguide. One or more light sources emit light into the array of coupling lightguides. Light from each coupling lightguide combines and totally internally reflects within the lightguide region. Light extraction features frustrate totally internally reflect light within the lightguide region such that the light exits the lightguide toward the reflective spatial light modulator in a light emitting region of the film. A cladding region is optically coupled to the lightguide so light from the light source propagates into the cladding region. A light extracting region is operatively coupled to the cladding region opposite the lightguide, and light in the cladding region is extracted. A method of producing a display is also disclosed.
1. A reflective display comprising:
a. a reflective spatial light modulator; and
b. a frontlight comprising:
i). a lightguide formed from a film having opposing faces with a thickness not greater than about 0.5 millimeters therebetween, the lightguide having an array of coupling lightguides continuous with a lightguide region of the lightguide, wherein:
a). each coupling lightguide terminates in a bounding edge; and
b). each coupling lightguide is folded in a fold region such that the bounding edges are stacked;
ii). at least one light source disposed to emit light into the stacked bounding edges, the light propagating within the coupling lightguides to the lightguide region of the lightguide, with light from each coupling lightguide combining and totally internally reflecting within the lightguide region;
iii). a plurality of light extraction features that frustrate totally internally reflected light within the lightguide region such that the light exits the lightguide toward the reflective spatial light modulator in a light emitting region of the film;
iv). a cladding region optically coupled on a first side to the lightguide wherein light from the at least one light source propagates into the cladding region; and
v). a light extracting region operatively coupled to the cladding region on a second side of the cladding region opposite the lightguide,
wherein a portion of light in the cladding region is extracted by the light extracting region.
2. The reflective display of claim 1 wherein each coupling lightguide is folded to a radius of curvature of less than 75 times an average thickness of the coupling lightguide and the portion of light comprises light propagating at higher angles in the lightguide after the fold region than before the fold region.
3. The reflective display of claim 1 wherein the light extracting region comprises a light absorbing material that extracts and absorbs light from the cladding region.
4. The reflective display of claim 1 wherein the light emitting region of the lightguide has an average luminous transmittance greater than 70% when measured according to ASTM D1003 version 07e1 when the at least one light source is not emitting light.
5. The reflective display of claim 1 wherein the light emitting region of the lightguide has an average luminous transmittance greater than 80% when measured according to ASTM D1003 version 07e1 when the at least one light source is not emitting light.
6. The reflective display of claim 1 wherein the light emitting region of the lightguide has an average haze less than 30% when measured according to ASTM D1003 version 07e1 when the at least one light source is not emitting light.
7. The reflective display of claim 1 wherein the light emitting region of the lightguide has an average haze less than 10% when measured according to ASTM D1003 version 07e1 when the at least one light source is not emitting light.
8. The reflective display of claim 1 wherein a region of the lightguide comprising the plurality of light extraction features has an optical property of reflecting light with a luminance less than 100 cd/m 2 when the region is illuminated with 1000 lux of diffuse light from a light integrating sphere incident on a surface of the lightguide from a side of the lightguide opposite a light trap box when the region is disposed across an opening of the light trap box comprising a black, light absorbing material lining walls of the light trap box and the at least one light source is not emitting light.
9. The reflective display of claim 1 wherein a region of the lightguide comprising the light extraction features has an optical property of reflecting light with a luminance less than 50 cd/m 2 when the region is illuminated with 1000 lux of diffuse light from a light integrating sphere incident on a surface of the lightguide from a side of the lightguide opposite a light trap box when the region is disposed across an opening of the light trap box comprising a black, light absorbing material lining the walls and the at least one light source is not emitting light.
10. The reflective display of claim 1 wherein a region of the lightguide comprising the light extraction features has an optical property of reflecting light with a luminance less than 10 cd/m 2 when the region is illuminated with 400 lux of diffuse light from a light integrating sphere incident on a surface of the lightguide from a side of the lightguide opposite a light trap box when the region is disposed across an opening of the light trap box comprising a black, light absorbing material lining the walls and the at least one light source is not emitting light.
11. The reflective display of claim 1 wherein an average lateral dimension of the plurality of light extraction features in the light emitting region in a direction parallel to an optical axis of the light propagating within the lightguide at the plurality of light extraction features is less than 500 microns.
12. The reflective display of claim 1 wherein the lightguide is folded such that a region of the lightguide is disposed behind the reflective spatial light modulator.
13. The reflective display of claim 1 wherein the light extracting region is a layer optically coupled to the cladding region on a surface of the cladding region opposite the lightguide.
14. The reflective display of claim 1 wherein the cladding region is a layer optically coupled on a first side to the lightguide and the light extracting region comprises surface relief features on a second side of the layer opposite the first side of the layer.
15. The reflective display of claim 1 wherein the light extracting region is positioned within a layer of a cladding material, and the cladding region is defined by a region of the layer of the cladding material positioned between the lightguide and the light extracting region.
16. The reflective display of claim 1 wherein the light extracting region comprises a light scattering region that extracts light from the cladding region.
17. The reflective display of claim 16 wherein the light scattering region comprises a plurality of surface relief features on a surface of the cladding region.
18. The reflective display of claim 1 comprising a cladding layer optically coupled to the lightguide in the light emitting region.
19. The reflective display of claim 18 wherein the cladding layer comprises an adhesive material.
20. The reflective display of claim 1 comprising a light mixing region of the lightguide disposed between folds in the coupling lightguides and the light emitting region, wherein light from each coupling lightguide combines and totally internally reflects within the light mixing region.
21. The reflective display of claim 20 wherein the lightguide is folded in the light mixing region such that a region of the lightguide is disposed behind the reflective spatial light modulator.
22. A reflective display comprising:
a reflective spatial light modulator; and
a frontlight comprising:
a lightguide formed from a film having a thickness not greater than 0.5 millimeters, the lightguide comprising an array of coupling lightguides extending from a lightguide region of the lightguide, the array of coupling lightguides folded in a fold region and stacked to form a light input surface;
a light source disposed to emit light into the light input surface, the light propagating within the array of coupling lightguides to the lightguide region, with light from each coupling lightguide of the array of coupling lightguides combining and totally internally reflecting within the lightguide region;
a plurality of light extraction features operatively coupled to the film and configured to frustrate the totally internally reflected light within the lightguide region such that the light exits the frontlight in a light emitting region toward the reflective spatial light modulator;
a cladding region optically coupled to the lightguide;
a light extracting region operatively coupled to the cladding region on a first side of the cladding region opposite the lightguide,
wherein light propagating in each coupling lightguide at a first angle from a total internal reflection interface is propagating at a second angle greater than the first angle after the fold region in the coupling lightguide and is extracted from the cladding region by the light extracting region.
23. The reflective display of claim 22 wherein the light extracting region is a light absorbing region.
24. The reflective display of claim 22 wherein the light extracting region is a light scattering region.