Direct lit backlight with light recycling and source polarizers

• US 20060187650A1
• Filed: 02/24/2005
• Published: 08/24/2006
• Est. Priority Date: 02/24/2005
• Status: Abandoned Application

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: O'Neill, Mark B., Epstein, Kenneth A.
• Application Number:
  US11/064,685
• Publication Number:
  US 20060187650A1
• Time in Patent Office: Days
• US Class Current: 362/19
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

Direct lit backlights and associated methods are disclosed in which typically an array of light sources is disposed between a back reflector and a front reflective polarizer. Source polarizers are provided to cover the light sources. Light that passes through the source polarizer towards the front reflective polarizer is partially transmitted and partially reflected by the front reflective polarizer. The partial transmission and reflection can be balanced to enhance illumination uniformity over the output face of the backlight. Direct lit backlights having arrays of polarized light sources are also disclosed, including backlights in which the light sources use LED light sources, and backlights in which the polarized light sources are substantially aligned with each other.

Claims

1. A direct lit backlight having an output face, comprising:

a front reflective polarizer;

a back reflector;

a light source disposed between the reflective polarizer and the back reflector; and

a source polarizer at least partially covering the light source;

wherein light transmitted through the source polarizer is partially transmitted and partially reflected by the front reflective polarizer.

2. The backlight of claim 1, wherein the light source is selected from the group of a fluorescent lamp and a light emitting diode (LED).

3. The backlight of claim 1, wherein the source polarizer comprises a reflective polarizer.

4. The backlight of claim 1, wherein the light source is one of a plurality of light sources disposed between the front reflective polarizer and the back reflector.

5. The backlight of claim 4, wherein the source polarizer is one of a plurality of source polarizers, each source polarizer at least partially covering a corresponding one of the light sources.

6. The backlight of claim 5, wherein at least some of the plurality of source polarizers are partially crossed with the front reflective polarizer.

7. The backlight of claim 1, wherein the back reflector is polarization converting.

8. The backlight of claim 1, wherein the front reflective polarizer is selected from the group of specularly reflective polarizers and diffusely reflective polarizers.

9. The backlight of claim 1, further comprising a diffusely transmissive layer disposed atop the front reflective polarizer.

10. The backlight of claim 1 in combination with a display panel.

11. The backlight of claim 1, wherein the front reflective polarizer has lateral dimensions commensurate with the output face, and the source polarizer is smaller in plan view area than the output face.

12. A direct lit backlight, comprising:

a front reflective polarizer;

a back reflector; and

an array of polarized light sources disposed between the reflective polarizer and the back reflector.

13. The backlight of claim 12, wherein the light sources are arranged such that light emitted by the light sources is partially transmitted and partially reflected by the front reflective polarizer.

14. The backlight of claim 12, wherein the back reflector is polarization converting.

15. The backlight of claim 12, wherein the light sources comprise LEDs.

16. The backlight of claim 12, wherein the light sources have polarization orientations that are substantially the same.

17. A method of making a direct lit backlight, comprising:

providing a front reflective polarizer and a polarization-converting back reflector;

positioning a polarized light source between the front reflective polarizer and the back reflector; and

orienting the polarized light source relative to the front reflective polarizer to achieve a desired illumination across the backlight.

18. The method of claim 17, the orienting step includes orienting the polarized light source such that light emitted by the polarized light source is partially transmitted and partially reflected by the front reflective polarizer.

19. The method of claim 17, wherein the backlight has an output face, and wherein the orienting step is carried out to enhance brightness uniformity at the output face.

20. The method of claim 17, wherein the orienting step includes rotating at least one of the front reflective polarizer and the polarized light source.

21. The method of claim 17, wherein the polarized light source in the providing step is one of a plurality of polarized light sources provided between the front reflective polarizer and the polarization-converting back reflector.

22. The method of claim 21, wherein the tailoring step includes rotating at least some of the polarized light sources.