Dark state light recycling film and display

• US 20060109398A1
• Filed: 11/19/2004
• Published: 05/25/2006
• Est. Priority Date: 11/19/2004
• Status: Active Grant

• Current Assignee: SKC Hi-Tech & Marketing Co., Ltd.
• Original Assignee: Eastman Kodak Company
• Inventors: Mi, Xiang-Dong
• Granted Patent: US 7,301,592 B2
• Time in Patent Office: Days
• US Class Current: 349/96
• 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
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336

Abstract

A liquid crystal display has a backlight unit for providing substantially unpolarized illumination, a rear polarizer proximate the backlight unit for receiving the incident substantially unpolarized illumination and transmitting substantially polarized illumination. A liquid crystal spatial light modulator forms a modulated beam by selective, pixel-wise modulation of the polarization of the substantially polarized illumination. A color filter array transmits selected wavelengths of the modulated beam from the LC spatial light modulator. A front polarizer has a transmission axis for transmitting the portion of the modulated beam having polarization in alignment with the transmission axis. A reflective polarizing element is disposed between the liquid crystal spatial light modulator and the front polarizer for reflecting a portion of dark state light back toward the backlight unit.

Claims

1. A liquid crystal display comprising

(a) a backlight unit for providing illumination;

(b) a rear polarizer disposed proximate the backlight unit for receiving the incident illumination and transmitting substantially polarized illumination;

(c) a liquid crystal spatial light modulator for forming a modulated beam by selective, pixel-wise modulation of the polarization of the substantially polarized illumination;

(d) a color filter array for transmitting selected wavelengths of the modulated beam from the LC spatial light modulator;

(e) a front polarizer having a transmission axis for transmitting the portion of the modulated beam having a polarization in alignment with the transmission axis; and

,

(f) a reflective polarizing element disposed between the liquid crystal spatial light modulator and the front polarizer, the reflective polarizing element reflecting a portion of dark state light back toward the backlight unit.

2. A liquid crystal display according to claim 1 wherein the reflective polarizing element is coupled to the surface of the liquid crystal spatial light modulator.

3. A liquid crystal display according to claim 1 wherein the color filter array is coupled to the surface of the liquid crystal spatial light modulator.

4. A liquid crystal display according to claim 1 wherein the transmittance of the reflective polarizing element is greater than 75%.

5. A liquid crystal display according to claim 1 further comprising an additional reflective polarizer disposed between the rear polarizer and the backlight unit.

6. A liquid crystal display according to claim 1 further comprising a collimating film disposed between the rear polarizer and the backlight unit.

7. A liquid crystal display according to claim 1 further comprising a compensation film coupled with the reflective polarizer.

8. A liquid crystal display according to claim 1 wherein the respective transmission axes of the front and rear polarizers are parallel to each other to within +/−

10 degrees.

9. A liquid crystal display according to claim 1 wherein the respective transmission axes of the front and rear polarizers are perpendicular to each other, to within +/−

10 degrees.

10. A liquid crystal display according to claim 1 wherein the respective transmission axes of the front polarizer and the reflective polarizing element are parallel to each other, to within about +/−

10 degrees.

11. A liquid crystal display according to claim 1 wherein the reflective polarizing element comprises a wire grid polarizer.

12. A liquid crystal display according to claim 1 wherein the reflective polarizing element comprises a multilayer interference-based polarizer.

13. A liquid crystal display according to claim 1 wherein the reflective polarizing element comprises a cholesteric polarizer with a quarter wave retarder.

14. A liquid crystal display according to claim 1 wherein the backlight unit comprises at least one light emitting diode.

15. A liquid crystal display according to claim 1 wherein the reflective polarizing element is a reflective polarization color filter array.

16. A liquid crystal display according to claim 15 wherein the reflective polarization color filter array comprises:

a) a reflective polarizer; and

,

b) a reflective color filter array, disposed between the reflective polarizer and the front polarizer.

17. A liquid crystal display according to claim 15 wherein the reflective polarization color filter array comprises:

a) a reflective color filter array; and

,

b) a reflective polarizer disposed between the reflective color filter array and the front polarizer.

18. A liquid crystal display according to claim 1 wherein the backlight unit emits linearly polarized light.

19. A liquid crystal display according to claim 18 wherein the backlight unit further comprises a reflective polarizer.

20. A liquid crystal display according to claim 18 wherein the color filter array is disposed between the reflective polarizing element and the front polarizer.

21. A liquid crystal display according to claim 18 wherein the reflective polarizing element is disposed between the color filter array and the front polarizer.

22. A liquid crystal display according to claim 1 further comprising a reflective color filter array disposed between the backlight unit and the rear polarizer.

23. A liquid crystal display according to claim 22 wherein the color filter array is disposed between the reflective polarizing element and the front polarizer.

24. A liquid crystal display according to claim 1 wherein the backlight unit is a color separation backlight unit.

25. A liquid crystal display according to claim 22 wherein the reflective polarizing element is disposed between the color filter array and the front polarizer.

26. A liquid crystal display according to claim 1 further comprising a reflective polarization color filter array disposed between the backlight and the rear polarizer.

27. A liquid crystal display according to claim 26 wherein the color filter array is disposed between the reflective polarizing element and the front polarizer.

28. A liquid crystal display according to claim 26 wherein the reflective polarizing element is disposed between the color filter array and the front polarizer.

29. A liquid crystal display according to claim 26 wherein the reflective polarization color filter array comprises:

a) a reflective polarizer; and

,

b) a reflective color filter array, disposed between the reflective polarizer and the backlight unit.

30. A liquid crystal display according to claim 15 wherein the color filter array is disposed adjacent to the reflective polarization color filter array.

31. A liquid crystal display according to claim 1 wherein the respective transmission axes of the front polarizer and the reflective polarizing element are orthogonal to each other, to within +/−

10 degrees.

32. A method for adjusting display brightness comprising:

a) providing backlight illumination to a transmissive liquid crystal display component;

b) forming a modulated beam by pixel-wise modulation of the polarization of the backlight illumination according to image data;

c) disposing a reflective polarizing color filter array in the path of the modulated beam;

d) determining, based on the image data, the relative proportion of dark pixels to light pixels; and

,

e) modulating the backlight illumination brightness level based on the relative proportion of dark to light pixels for the displayed image.

33. A method according to claim 32 wherein the step of modulating the backlight illumination brightness level comprises the step of varying the drive current to an light emitting diode.