LCD display backlight system with improved color mixing and efficiency

• US 20070053178A1
• Filed: 09/06/2006
• Published: 03/08/2007
• Est. Priority Date: 09/06/2005
• Status: Active Grant

• Current Assignee: Wavien, Inc.
• Original Assignee: Wavien, Inc.
• Inventors: Li, Kenneth, Inatsugu, Seiji
• Granted Patent: US 7,357,558 B2
• Time in Patent Office: Days
• US Class Current: 362/97.300
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133605 including specially adapted reflectors
• CPC Class Codes: G02F 1/133609 including means for improving the color mixing, e.g. white
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n

Abstract

A LCD display backlight system with improved color mixing and efficiency comprises a reflective surface, a plurality of light sources mounted on the reflective surface, a plurality of fractional wave plates and a reflective polarizer. The plurality of fractional wave plates is mounted on spaces between the plurality of light sources on the reflective surface. The reflective polarizer transmits light having a useable polarization and reflects back unused polarization of light onto the reflective surface. A portion of the unused polarization of light reflected from the reflective polarizer passes through a fractional wave plate. The reflective surface reflects the portion of the unused polarization of light through the fractional wave plate such that the polarization of the unused polarization of light is changed to useable polarization, thereby recycling the unused polarization of light into useful light.

Claims

1. A LCD display backlight system, comprising:

a reflective surface;

a plurality of light sources mounted on said reflective surface;

a plurality of fractional wave plates mounted on spaces between said plurality of light sources on said reflective surface; and

a reflective polarizer for transmitting light having a useable polarization and reflecting back unused polarization of light onto said reflective surface; and

wherein a portion of said unused polarization of light reflected from said reflective polarizer passes through a fractional wave plate and said reflective surface reflects said portion of said unused polarization of light through said fractional wave plate such that the polarization of said unused polarization of light is changed to useable polarization, thereby recycling said unused polarization of light into useful light.

2. The LCD display backlight system of claim 1, wherein said plurality of light sources are LEDs.

3. The LCD display backlight system of claim 2, wherein said plurality of LEDs are in chip form.

4. The LCD display backlight system of claim 2, wherein said plurality of LEDs are mounted and molded in lenses.

5. The LCD display backlight system of claim 2, wherein each of said plurality of LEDs generates either red, green or blue light.

6. The LCD display backlight system of claim 5, wherein said portion of unused polarization of light from a LED is reflected one or more times before passing through said fractional wave plate, thereby mixing the colors of light from said plurality of LEDs.

7. The LCD display backlight system of claim 1, further comprising a LCD panel;

and wherein said reflective polarizer transmits said light having useable polarization to said LCD panel.

8. The LCD display backlight system of claim 1, wherein said unused polarization propagates between said reflective surface and said reflective polarizer one or more time before being transmitted by said reflective polarizer.

9. The LCD display backlight system of claim 1, wherein said reflective polarizer is integrated with a diffuser.

10. The LCD display backlight system of claim 1, wherein said plurality of light sources are cold cathode fluorescent lamps.

11. The LCD display backlight system of claim 1, wherein said plurality of fractional wave plates form a pattern on said reflective surface.

12. The LCD display backlight system of claim 11, wherein said pattern is one of the following:

stripes, circles, rings centered around a light source, squares, rectangles, other geometric shapes, random shapes or regular shapes distributed randomly on said reflective surface.

13. The LCD display backlight system of claim 1, wherein each light sources are spaced S apart and said plurality of light sources are thickness T from said reflective polarizer.

14. The LCD display backlight system of claim 13, wherein density and coverage percentage of said fractional wave plates on said reflective surface are optimized based on said spacing S and said thickness T and determines the amount of color mixing with said system.

15. The LCD display backlight system of claim 1, wherein said fractional wave plates fully or partially covers the spaces between said plurality of light sources.

16. The LCD display backlight system of claim 1, wherein said plurality of fractional wave plates comprises quarter wave plates, half wave plates and/or other fractional multiples of a wave.

17. The LCD display backlight system of claim 1, wherein the output of a single pass of light through a fractional wave plate is non-circular.

18. The LCD display backlight system of claim 17, wherein the output of a second pass of light thorough said fractional wave plate is non-orthogonal to the incident light.

19. The LCD display backlight system of claim 18, wherein the output of said second pass of light does not match the polarization of said reflective polarizer and results in only partial transmission.

20. The LCD display backlight system of claim 19, wherein reflected portion of the output of second pass of light not transmitted by said reflective polarizer propagates between said reflective surface and said reflective polarizer one or more times before being transmitted by said reflective polarizer.

21. The LCD display backlight system of claim 1, wherein said plurality of fractional wave plates are not aligned to match the direction of the polarization of said reflective polarizer such that the output of a second pass of light through said plurality of fractional wave plates are non-orthogonal to the incident light.

22. The LCD display backlight system of claim 1, further comprising a LCD panel having four side panels, each side panel comprising one of the following:

an array of LEDs or cold cathode fluorescent lamps, a reflective surface, absorptive surface or partially reflective surface.

23. The LCD display backlight system of claim 22, wherein said panel comprising said array of LEDs or cold cathode fluorescent lamps further comprises polarization plates to provide polarized light.

24. The LCD display backlight system of claim 22, further comprising a polarization recovery system or a polarization recycling system.

25. The LCD display backlight system of claim 24, further comprising a polarization beam splitter and a fractional wave plate to provide polarized light output.

26. The LCD display backlight system of claim 22, wherein said panel comprising said array of LEDs or cold cathode fluorescent lamps further comprises an optional reflective surface;

and further comprising a reflective polarizer to reflect part of the light back into said side panels comprising said array of LEDs or cold cathode fluorescent lamps to provide a return light and said optional reflective surface reflecting said return light back to said reflective polarizer.

27. A LCD display backlight system, comprising:

a reflective surface;

a plurality of light sources mounted on said reflective surface;

a reflective polarizer for transmitting light having a useable polarization and reflecting back unused polarization of light onto said reflective surface;

a plurality of fractional wave plates located between said reflective polarizer and said reflective surface; and

wherein a portion of said unused polarization of light reflected from said reflective polarizer passes through a fractional wave plate and said reflective surface reflects said portion of said unused polarization of light through said fractional wave plate such that the polarization of said unused polarization of light is changed to useable polarization, thereby recycling said unused polarization of light into useful light.

28. The LCD display backlight system of claim 27, wherein said plurality of fractional wave plates are attached to said reflective polarizer.