Elimination of stitch artifacts in a planar illumination area

1. A planar illumination area comprising:

a first discrete light-guide element comprising (i) a first light source emitting light therein, (ii) first and second adjacent non-parallel sidewalls spanning top and bottom surfaces, and (iii) a first out-coupling region in the top surface; and

a second discrete light-guide element in contact with the first discrete light-guide element and comprising (i) a second light source, different from the first light source, emitting light therein, (ii) first and second adjacent non-parallel sidewalls spanning top and bottom surfaces, and (iii) a second out-coupling region in the top surface, only a portion of the second out-coupling region, including at least one sidewall of the second light-guide element, being disposed over and overlapping only a portion of the first out-coupling region including at least one sidewall of the first light-guide element, to define an overlapping region having an area,

wherein (i) a light output power of the first out-coupling region within the overlapping region is less than a light output power of the first out-coupling region outside the overlapping region and (ii) a light output power of the second out-coupling region within the overlapping region is less than a light output power of the second out-coupling region outside the overlapping region, whereby the overlapping region emits a substantially uniform light output power over the area.

2. The planar illumination area of claim 1 , wherein the light output power of the overlapping region differs from the light output power of the first and second out-coupling regions outside the overlapping region by no more than 10%.

3. The planar illumination area of claim 2 , wherein the change in light output power between the overlapping region and the first and second out-coupling regions outside the overlapping region is gradual.

4. The planar illumination area of claim 1 , wherein the first out-coupling region comprises light-scattering elements therein, a density of the light-scattering elements disposed within the first out-coupling region outside the overlapping region being greater than a density of the light-scattering elements disposed within the first out-coupling region inside the overlapping region.

5. The planar illumination area of claim 4 , wherein the density of the light-scattering elements inside the overlapping region decreases along one direction.

6. The planar illumination area of claim 1 , wherein the second out-coupling region is transparent in the overlapping region so as not to augment light emitted from the first out-coupling region.

7. The planar illumination area of claim 6 , wherein, in the overlapping region, light emitted from the first out-coupling region passes through the second out-coupling region.

8. The planar illumination area of claim 1 , further comprising a third discrete light-guide element comprising a third out-coupling region in its top surface, only a portion of the third out-coupling region overlapping only a second portion of the second out-coupling region to define a second overlapping region different from the overlapping region and having a second area, wherein the second overlapping region emits a substantially uniform light output power over the second area.

9. The planar illumination area of claim 1 , wherein at least a portion of the first sidewall of the first light-guide element (i) is non-vertical and (ii) forms a non-right angle with at least one of the top or bottom surfaces of the first light-guide element, and at least a portion of the first sidewall of the second light-guide element (i) is non-vertical, (ii) forms a non-right angle with at least one of the top or bottom surfaces of the second light-guide element, and (iii) is complementary to the first sidewall of the first light-guide element, the first sidewalls of the first and second light-guide element being disposed beneath a top surface of the second light-guide element in the overlapping region.

10. The planar illumination area of claim 9 , wherein a top surface of the planar illumination area comprises the top surfaces of the first and second light-guide elements and is substantially flat.

11. The planar illumination area of claim 1 , further comprising additional discrete light-guide elements forming, with the first and second light-guide elements, an array extending in first and second non-parallel directions, wherein the light-guide elements overlap in the first direction and do not overlap in the second direction.

12. The planar illumination area of claim 1 , further comprising additional discrete light-guide elements forming, with the first and second light-guide elements, an array extending in first and second non-parallel directions, wherein the light-guide elements overlap in the first and second directions.

13. The planar illumination area of claim 1 , wherein the overlapping region comprises a light-absorbing material.

14. The planar illumination area of claim 1 , wherein at least a portion of a sidewall of the first light-guide element comprises a reflective coating.

15. The planar illumination area of claim 1 , wherein at least a portion of a sidewall of the second light-guide element comprises a reflective coating.

16. The planar illumination area of claim 1 , wherein only a portion of a top surface of at least one of the first light-guide element or the second light-guide element is a light-absorbing surface.

17. A method of forming a planar illumination area, the method comprising:

providing a first discrete light-guide element comprising (i) a first light source emitting light therein, (ii) first and second non-parallel sidewalls spanning top and bottom surfaces, and (iii) a first out-coupling region in the top surface; and

disposing beneath and overlapping only a portion of the first light-guide element with a second discrete light-guide element comprising (i) a second light source, different from the first light source, emitting light therein, (ii) first and second non-parallel sidewalls spanning top and bottom surfaces, and (iii) a second out-coupling region in the top surface, thereby forming an overlapping region comprising only a portion of the first out-coupling region including at least one sidewall of the first light-guide element and only a portion of the second out-coupling region including at least one sidewall of the second light-guide element,

wherein (i) a light output power of the first out-coupling region within the overlapping region is less than a light output power of the first out-coupling region outside the overlapping region and (ii) a light output power of the second out-coupling region within the overlapping region is less than a light output power of the second out-coupling region outside the overlapping region, whereby the overlapping region emits a substantially uniform light output power.

18. A planar illumination area comprising:

a first discrete light-guide element comprising a polished sidewall disposed between a top surface and a bottom surface of the first light-guide element; and

a second discrete light-guide element comprising a polished sidewall disposed between a top surface and a bottom surface of the second light-guide element, the polished sidewall of the second light-guide element being adjacent to the polished sidewall of the first light-guide element,

wherein the second light-guide element receives light from the first light-guide element through the polished sidewalls, and light is refracted as it travels from the first light-guide element to the second light-guide element.

19. The planar illumination area of claim 18 , further comprising an index-matching material located between the sidewalls, an index of refraction of the index-matching material being approximately equal to an index of refraction of at least one of the first light-guide element or the second light-guide element.

20. The planar illumination area of claim 18 , wherein the first and second polished sidewalls are polished to a tolerance less than approximately 600 nm peak-to-peak.

21. A planar illumination area comprising:

a first discrete light-guide element comprising a sidewall disposed between a light-emitting top surface and a bottom surface of the first light-guide element;

a second discrete light-guide element comprising a sidewall disposed between a light-emitting top surface and a bottom surface of the second light-guide element, the first and second light-guide elements being butted together or only partially overlapping such that their light-emitting top surfaces collectively form a single continuous illumination surface including at least one of the sidewalls; and

an index-matching material covering the sidewalls, an index of refraction of the index-matching material being approximately equal to an index of refraction of at least one of the first light-guide element or the second light-guide element,

wherein light travels between the first and second light-guide elements, and, in a direction of travel from the first light-guide element to the second light-guide element, an intensity of light emitted by the continuous illumination surface changes continuously and monotonically notwithstanding the included sidewalls.

22. The planar illumination area of claim 21 , wherein the sidewall of the second light-guide element is adjacent to the sidewall of the first light-guide element and the index-matching material is located between the sidewalls.

23. The planar illumination of claim 21 , wherein the first and second light-guide elements only partially overlap, and the index-matching material is disposed over and in direct contact with the first and second light-guide elements to create a smooth surface thereover.