Liquid crystal flat panel display with enhanced backlight brightness and specially selected light sources

• US 6,243,068 B1
• Filed: 05/29/1998
• Issued: 06/05/2001
• Est. Priority Date: 05/29/1998
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Silicon Graphics Incorporated (Graphics Properties Holdings, Inc.)
• Inventors: Evanicky, Daniel E., Lu, Sun
• Primary Examiner(s): CHANG, KENT WU
• Application Number:
  US09/087,280
• Time in Patent Office: 1,103 Days
• Field of Search: 345/87, 345/102, 345/147, 345/150, 345/126, 348/223, 348/69-71, 362/31, 362/26, 362/62, 349/61, 349/62
• US Class Current: 345/102
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0076 Stacked arrangements of multiple light guides of the same or different cross-sectional area
• CPC Class Codes: G02F 1/133507 Films for enhancing the luminance
• CPC Class Codes: G02F 1/133609 including means for improving the color mixing, e.g. white
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one

Abstract

A multiple light source flat panel liquid crystal display (LCD) system having enhanced backlight brightness and specially selected light sources. According to the present invention, brightness in the LCD is enhanced by polarization recycling using a pre-polarizing film to pre-polarize light, and a special reflector for recycling light reflected by the pre-polarizing film. In one embodiment, the pre-polarizing film comprises a layer of DBEF brightness enhancement film, and the rear reflector is made of a PTFF material. In another embodiment, the rear reflector is covered with a film comprising barium sulfate. The multiple light sources are selected such that, at any color temperature within a predetermined range, the brightness of the LCD is not reduced below a given threshold minimum (e.g., 70 percent of the maximum brightness). Another constraint for selecting the light sources is that within the predetermined color temperature range, the color temperature is held close to the black body curve of the CIE chromaticity diagram. The light sources are also selected so that their maximum brightness point is set to be near the middle of the predetermined color temperature range. In furtherance of one embodiment of the present invention, the light sources selection process may be implemented in computer readable codes executable by a computer system such that a large number of number of light sources candidates may be simulated to obtain their luminance, chromaticity, and color temperature data.

Claims

1. A flat panel display (FPD) comprising:

a light distributor for distributing light towards a rear polarizer of said FPD, said rear polarizer polarizing light a predetermined orientation;

a pre-polarizer interposed between said light distributor and said rear polarizer and on a first side of said light distributor for allowing a first portion of light polarized in said predetermined orientation to pass, wherein a second portion of light is reflected towards a second side of said light distributor; and

a reflector for increasing brightness of said FPD, said reflector being positioned on said second side of said light distributor to receive said second portion of light, said reflector further having a layer of light rephasing material for rephasing said second portion of light into said predetermined orientation such that a part of said second portion of light is allowed to pass through said pre-polarizer and said rear polarizer, and wherein said rear polarizer, said light distributor, said pre-polarizer, and said reflector are positioned on one side relative to a liquid crystal display (LCD) layer of said FPD.

2. The flat panel display according to claim 1 wherein said light rephasing material comprises a PTFF material.

3. The flat panel display according to claim 1 wherein said pre-polarizer comprises a layer of dual brightness enhancement film (DBEF).

4. The flat panel display according to claim 2 wherein said light distributor comprises:

a first planar light pipe disposed to provide a first spectral component of backlight to said liquid crystal display (LCD) layer, said first spectral component having a first color temperature; and

a second planar light pipe disposed parallel to said first planar light pipe to provide a second spectral component of backlight to said LCD layer;

said second spectral component having a second color temperature,

wherein said first color temperature is below a predefined minimum color temperature, and wherein said second color temperature is above a predefined maximum color temperature.

5. The flat panel display according to claim 4 wherein said first color temperature is approximately 3,560 K.

6. The flat panel display according to claim 4 wherein said second color temperature is approximately 15,000 K.

7. The flat panel display according to claim 2 further comprising:

a light diffusing film disposed between said pre-polarizer and said rear polarizer for eliminating off-axis defects.

8. The flat panel display according to claim 7 wherein said light diffusing film comprises a LEXAN film.

9. The flat panel display according to claim 4 further comprising:

a first light source coupled to said first planar light pipe for emitting said first spectral component; and

a second light source coupled to said second planar light pipe for emitting said second spectral component,

wherein a color temperature of said flat panel display is adjustable by selectively and independently varying brightnesses of said first light source and said second light source.

10. The flat panel display according to claim 4 further comprising a crossed brightness enhancement film (BEF) interposed between said light distributor and said rear polarizer of said LCD screen for expanding a view angle of said LCD screen.

11. The flat panel display according to claim 1 wherein said light rephasing material comprises a material including barium sulfate.

12. The flat panel display according to claim 11 wherein said light distributor comprises:

a first planar light pipe disposed to provide a first spectral component of backlight to said liquid crystal display (LCD) layer, said first spectral component having a first color temperature; and

a second planar light pipe disposed parallel to said first planar light pipe to provide a second spectral component of backlight to said LCD layer;

said second spectral component having a second color temperature,

wherein said first color temperature is below a predefined minimum color temperature, and wherein said second color temperature is above a predefined maximum color temperature.

13. The flat panel display according to claim 12 further comprising:

a first light source coupled to said first planar light pipe for emitting said first spectral component; and

a second light source coupled to said second planar light pipe for emitting said second spectral component,

wherein a color temperature of said flat panel display is adjustable by selectively and independently varying a brightness of said first light source and said second light source.

14. A flat panel display (FPD) comprising:

a light distributor operable to distribute light towards a rear polarizer of said FPD, said rear polarizer polarizing light a predetermined orientation;

a pre-polarizer interposed between said light distributor and said rear polarizer and on a first side of said light distributor and operable to allow a first portion of light polarized in said predetermined orientation to pass, wherein a second portion of light is reflected towards a second side of said light distributor; and

a reflector operable to increase brightness of said FPD, said reflector being positioned on said second side of said light distributor to receive said second portion of light, said reflector further having a layer of light rephasing material operable to rephase said second portion of light into said predetermined orientation wherein a part of said second portion of light is allowed to pass through said pre-polarizer and said rear polarizer, and wherein said rear polarizer said light distributor, said pre-polarizer, and said reflector are positioned on one side relative to a liquid crystal display (LCD) layer of said FPD.

15. The flat panel display according to claim 14 wherein said light rephasing material comprises a PTFF material.

16. The flat panel display according to claim 14 wherein said pre-polarizer comprises a layer of dual brightness enhancement film (DBEF).

17. The flat panel display according to claim 15 wherein said light distributor comprises:

a first planar light pipe disposed to provide a first spectral component of backlight to said liquid crystal display (LCD) layer, said first spectral component having a first color temperature; and

a second planar light pipe disposed parallel to said first planar light pipe to provide a second spectral component of backlight to said LCD layer;

said second spectral component having a second color temperature,

wherein said first color temperature is below a predefined minimum color temperature, and wherein said second color temperature is above a predefined maximum color temperature.

18. The flat panel display according to claim 17 wherein said first color temperature is approximately 3,560 K.

19. The flat panel display according to claim 17 wherein said second color temperature is approximately 15,000 K.

20. The flat panel display according to claim 15 further comprising:

a light diffusing film disposed between said pre-polarizer and said rear polarizer and operable to eliminate off-axis defects.

21. The flat panel display according to claim 20 wherein said light diffusing film comprises a LEXAN film.

22. The flat panel display according to claim 17 further comprising:

a first light source coupled to said first planar light pipe and operable to emit said first spectral component; and

a second light source coupled to said second planar light pipe and operable to emit said second spectral component,

wherein a color temperature of said flat panel display is adjustable by selectively and independently varying brightnesses of said first light source and said second light source.

23. The flat panel display according to claim 17 further comprising a crossed brightness enhancement film (BEF) interposed between said light distributor and said rear polarizer of said LCD screen and operable to expand a view angle of said LCD screen.

24. The flat panel display according to claim 14 wherein said light rephasing material comprises a material including barium sulfate.

25. The flat panel display according to claim 24 wherein said light distributor comprises:

a first planar light pipe disposed to provide a first spectral component of backlight to said liquid crystal display (LCD) layer, said first spectral component having a first color temperature; and

a second planar light pipe disposed parallel to said first planar light pipe to provide a second spectral component of backlight to said LCD layer;

said second spectral component having a second color temperature,

wherein said first color temperature is below a predefined minimum color temperature, and wherein said second color temperature is above a predefined maximum color temperature.

26. The flat panel display according to claim 25 further comprising:

a first light source coupled to said first planar light pipe and operable to emit said first spectral component; and

a second light source coupled to said second planar light pipe and operable to emit said second spectral component,

wherein a color temperature of said flat panel display is adjustable by selectively and independently varying a brightness of said first light source and said second light source.