Thin Backlight Using Low Profile Side Emitting LEDs

• US 20090086508A1
• Filed: 09/27/2007
• Published: 04/02/2009
• Est. Priority Date: 09/27/2007
• Status: Abandoned Application

• Current Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Original Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Inventors: Bierhuizen, Serge
• Application Number:
  US11/863,167
• Publication Number:
  US 20090086508A1
• Time in Patent Office: Days
• US Class Current: 362/617
• CPC Class Codes: G02B 6/0018 Redirecting means on the surface of the light guide
• CPC Class Codes: G02B 6/0021 for housing at least a part of the light source, e.g. by forming holes or recesses
• CPC Class Codes: G02B 6/0023 provided by one optical element, or plurality thereof, placed between the light guide and the light source, or around the light source
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0065 Manufacturing aspects; Material aspects
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0073 Light emitting diode [LED]
• CPC Class Codes: G02B 6/0083 Details of electrical connections of light sources to drivers, circuit boards, or the like
• CPC Class Codes: G02F 1/133603 with LEDs
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: H01L 2224/14 of a plurality of bump connectors

Abstract

Backlights containing low profile, side-emitting LEDs are described that have improved brightness uniformity. In one embodiment, the backlight comprises a solid transparent lightguide with a plurality of openings in a bottom surface of the lightguide, each opening containing a side-emitting LED. Prisms or other optical features are formed in the top wall of each opening to reflect light in the lightguide towards a light output surface of the lightguide so that the side-emitting LEDs do not appear as dark spots at the output of the backlight. To avoid any direct emission from the sides of the LED toward the output surface of the lightguide appearing as bright areas, optical features are formed at the edges of the opening or in the output surface of the lightguide so that direct emission light is not output from the lightguide. Substantially identical cells may be formed in the lightguide using cellular walls around one or more LEDs.

Claims

1. A light emitting device comprising:

at least one side-emitting, non-lasing light emitting diode (LED), wherein a majority of light emitted normal to a top surface of a semiconductor LED die is redirected away from the normal; and

a lightguide having an output surface through which light is emitted,

the lightguide having at least one indention in a first surface, opposite the output surface, wherein each indention contains a side-emitting LED, walls of the indention forming part of the first surface,

the lightguide having optical features on at least one of the output surface and the first surface for limiting an appearance of dark areas over each LED or bright areas proximate to each LED, the optical features redirecting light to improve a uniformity of brightness across the output surface of the lightguide.

2. The device of claim 1 wherein the optical features comprise at least one optical feature formed in a top wall of the at least one indentation containing a respective LED, such that light within the lightguide impinging on an optical feature overlying each LED is redirected towards the output surface of the lightguide so the side-emitting LED does not appear as a dark spot at the output surface of the lightguide.

3. The device of claim 1 wherein the optical features comprise at least one optical feature formed in the output surface of the lightguide generally above a respective LED, such that light impinging on an optical feature above each LED is redirected so as to be emitted through the output surface generally above the LED so the side-emitting LED does not appear as a dark spot at the output surface of the lightguide.

4. The device of claim 1 wherein the optical features comprise at least one optical feature formed near side edges of a top wall of the at least one indentation containing a respective LED, such that direct light from the LED emitted towards the output surface of the lightguide is redirected away from the output surface of the lightguide so such direct light from the LED emitted towards the output surface of the lightguide does not appear as a bright spot at the output surface of the lightguide.

5. The device of claim 1 wherein the optical features comprise at least one optical feature formed in the output surface of the lightguide generally above a respective LED, such that direct light from the LED emitted towards the output surface of the lightguide is redirected away from the output surface of the lightguide so such direct light from the LED emitted towards the output surface of the lightguide does not appear as a bright spot at the output surface of the lightguide.

6. The device of claim 1 wherein the optical features comprise indented features.

7. The device of claim 1 wherein the optical features comprise prisms, hip-roofs, spheres, ellipsoids, pyramids, pits, bumps, or holes formed in or on a surface of the lightguide.

8. The device of claim 1 wherein the optical features are molded into a surface of the lightguide.

9. The device of claim 1 wherein the optical features comprise scattering reflectors deposited on a surface of the lightguide.

10. The device of claim 1 wherein the scattering reflectors comprise a white pigment.

11. The device of claim 1 wherein the LED has a thickness less than 2 mm.

12. The device of claim 1 further comprising a submount on which the LED is mounted.

13. The device of claim 1 wherein the LED further comprises a phosphor layer.

14. The device of claim 13 wherein the LED, including the phosphor layer, emits white light.

15. The device of claim 1 further comprising a phosphor layer overlying the output surface of the lightguide, wherein the side-emitting LED emits blue light.

16. The device of claim 1 wherein light emitting sides of the LED have a height less than 1 mm.

17. The device of claim 1 further comprising a reflector sheet adjacent the first surface for reflecting light toward the output surface.

18. The device of claim 1 further comprising a flexible circuit interconnecting a plurality of the LEDs.

19. The device of claim 1 further comprising a liquid crystal layer overlying the lightguide for selectively controlling pixels in a display screen.

20. The device of claim 1 further comprising a diffuser sheet over the lightguide.

21. The device of claim 1 wherein the lightguide is flexible and rolled up during fabrication.

22. The device of claim 1 wherein the side-emitting LED comprises collimation optics.

23. The device of claim 1 wherein the lightguide comprises a plurality of cells, each cell containing at least one LED, each cell comprising cell walls surrounding at least one LED, each cellular wall being at least partially reflective.

24. The device of claim 23 wherein the cell walls reflect light by total internal reflection.

25. The device of claim 23 wherein the cell walls comprise non-transparent reflective material.

26. The device of claim 23 wherein the cell walls are angled so as to redirect light towards the output surface of the light guide.

27. The device of claim 1 wherein the side-emitting LED comprises an active layer and reflector overlying the active layer, wherein the active layer and a bottom surface of the reflector facing the active layer are wholly located between the output surface and first surface of the lightguide.

28. The device of claim 1 wherein the lightguide has a thickness less than 10 mm.

29. A light emitting device comprising:

a plurality of side-emitting, non-lasing light emitting diodes (LED);

a lightguide having an output surface through which light is emitted, each LED being positioned within an opening in the lightguide so as to optically couple light into the lightguide; and

cellular walls within the lightguide at least partially surrounding one or more LEDs, each cellular wall being at least partially reflective, wherein the cellular walls create a plurality of cells in the lightguide, a light output from each cell being substantially the same.

30. The device of claim 29 wherein the cellular walls are diffusively reflective.

31. The device of claim 29 wherein the cellular walls are translucent.

32. The device of claim 29 wherein the cell walls are angled to redirect light to the output surface of the lightguide.

33. The device of claim 29 wherein at least some of the LEDs are in line with a cellular wall such that light from LEDs is divided between two or more cells.

34. The device of claim 29 wherein at least some of the LEDs are positioned at intersections of a plurality of cellular walls.

35. The device of claim 29 wherein the cells are modular such that cells may be added to increase a size of the light emitting device.

36. The device of claim 29 further comprising a liquid crystal display illuminated by the lightguide.

37. The device of claim 29 wherein the light output of each of the LEDs is individually controllable.

38. The device of claim 29 where the light output of each cell is separately controllable.

39. The device of claim 29 wherein the cellular walls extend between top and bottom surfaces of the lightguide.

40. The device of claim 29 wherein the cellular walls extend only part way between top and bottom surfaces of the lightguide.