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

• US 6,448,955 B1
• Filed: 06/08/2000
• Issued: 09/10/2002
• 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:
  US09/590,753
• Time in Patent Office: 824 Days
• Field of Search: 345/102, 345/87, 362/227, 362/230, 349/61, 349/68, 348/655, 348/649, 348/663
• 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 method of selecting light source candidates for an illumination system, said illumination system being white-balance adjustable over a predetermined color temperature range, the method comprising the steps of:

(a) varying a percentage composition of red, green and blue phosphors to generate a first set and a second set of light source candidates;

(b) from said first set and said second set, selecting a plurality of candidate pairs;

(c) calculating combined luminance spectrums for one candidate pair of the plurality of the candidate pairs across various brightness levels of said light sources candidates;

(d) from said combined luminance spectrums of said step (c), calculating a color temperature-luminance relationship for said candidate pair; and

(e) rejecting said candidate pair unless said color temperature-luminance relationship satisfies a predefined selection criterion.

2. The method according to claim 1 further comprising the steps of:

(f) from said combined luminance spectrums of said step (c) calculated across said various brightness levels, calculating a chromaticity relationship for said candidate pair over a predetermined color temperature range; and

(g) rejecting said candidate pair unless said chromaticity relationship satisfies said predefined selection criterion.

3. The method according to claim 1 further comprising the step of:

repeating said steps (c) to (e) for other candidate pairs of the plurality, of candidate pairs.

4. The method according to claim 1 wherein said step (e) further comprises the steps of:

analyzing said luminance-color temperature relationship; and

rejecting said candidate pair unless a predetermined luminance threshold is reached across said predetermined color temperature range.

5. The method according to claim 4 wherein said predetermined luminance threshold is 70% of a maximum luminance value of said candidate pair.

6. The method according to claim 4 wherein said predetermined color temperature range comprises a lower color temperature value of 5,000 K and a higher color temperature value of 6,500 K.

7. The method according to claim 1 wherein said step (e) further comprises the steps of:

analyzing said luminance-color temperature relationship; and

rejecting said candidate pair unless a maximum luminance occurs substantially within a middle range of said predetermined color temperature range.

8. The method according to claim 2 wherein said step (g) further comprises the steps of:

analyzing said chromaticity relationship;

comparing said chromaticity relationship to a CIE black body radiation curve over said color temperature range; and

rejecting said candidate pair unless said chromaticity relationship is similar to said CIE black body radiation curve.

9. A method of selecting light source candidates for an illumination system, said illumination system being white-balance adjustable over a predetermined color temperature range, the method comprising the steps of:

(a) varying a percentage composition of red, green and blue phosphors to generate a first set and a second set of light source candidates;

(b) from said first set and said second set, selecting a plurality of candidate pairs;

(c) calculating combined luminance spectrums for one candidate pair of the plurality of candidate pairs across various brightness levels of said light sources candidates;

(d) from said combined luminance spectrums of said step (c), calculating a color temperature-luminance relationship for said candidate pair;

(e) from said combined luminance spectrums, calculating a chromaticity relationship for said candidate pair over said various brightness levels;

(f) rejecting said candidate pair unless a predetermined luminance threshold is reached across said predetermined color temperature range, and unless said chromaticity relationship closely tracks the CIE black body radiation curve for said predetermined color temperature range.

10. The method according to claim 9 wherein further comprising the step of:

rejecting said candidate pair unless a maximum luminance occurs substantially within a middle range of said predetermined color temperature range.

11. A computer system comprising a processor coupled to a bus and a memory coupled to said bus wherein said memory contains instructions for implementing a method of selecting light source candidates for an illumination system, said illumination system being white-balance adjustable over a predetermined color temperature range, the method comprising the steps of:

(a) varying a percentage composition of red, green and blue phosphors to generate a first set and a second set of light source candidates;

(b) from said first set and said second set, selecting a plurality of candidate pairs;

(c) calculating combined luminance spectrums for one candidate pair of the plurality of candidate pairs across various brightness levels of said light sources candidates;

(d) from said combined luminance spectrums, calculating a color temperature-luminance relationship for said candidate pair; and

(e) rejecting said candidate pair unless said color temperature-luminance relationship satisfies a predefined selection criterion.

12. The computer system according to claim 11 wherein said method further comprises the steps of:

(f) from said combined luminance spectrums, calculating a chromaticity relationship for said candidate pair; and

(g) rejecting said pair unless said chromaticity relationship satisfies said predefined selection criterion.

13. The computer system according to claim 11 wherein said method further comprises the steps of:

repeating said steps (c) to (e) for other candidate pairs of the plurality.

14. The computer system according to claim 11 wherein said step (e) further comprises the steps of:

analyzing said luminance-color temperature relationship; and

rejecting said candidate pair unless a predetermined luminance threshold is reached across said predetermined color temperature range.

15. The computer system according to claim 14 wherein said predetermined luminance threshold is 70% of a maximum luminance value of said candidate pair.

16. The computer system according to claim 11 wherein said predetermined color temperature range comprises a lower color temperature value of 5,000 K and a higher color temperature value of 6,500 K.

17. The computer system according to claim 12 wherein said step (f) of said method further comprises the steps of:

analyzing said chromaticity relationship;

comparing said chromaticity relationship to a CIE black body radiation curve over said color temperature range; and

rejecting said candidate pair unless said chromaticity relationship is similar to said CIE black body radiation curve.

18. The computer system according to claim 11 wherein said step (e) of said method further comprises the steps of:

analyzing said luminance-color temperature relationship; and

rejecting said candidate pair unless a maximum luminance occurs substantially within a middle range of said predetermined color temperature range.

19. A computer readable medium having instructions stored thereon that when executed by a processor implement a method of selecting light source candidates for an illumination system, said illumination system being white-balance adjustable over a predetermined color temperature range, the method comprising the steps of:

(a) varying a percentage composition of red, green and blue phosphors to generate a first set and a second set of light source candidates;

(b) from said first set and said second set, selecting a plurality of candidate pairs;

(c) calculating combined luminance spectrums for one candidate pair of the plurality of candidate pairs across various brightness levels of said light sources candidates;

(d) from said combined luminance spectrums of said step (c), calculating a color temperature-luminance relationship for said candidate pair;

(e) from said combined luminance spectrums, calculating a chromaticity relationship for said candidate pair over said various brightness levels;

(f) rejecting said candidate pair unless a predetermined luminance threshold is reached across said predetermined color temperature range, and unless said chromaticity relationship closely tracks the CIE black body radiation curve for said predetermined color temperature range.

20. The computer readable medium according to claim 19 wherein said method further comprises the step of:

rejecting said candidate pair unless a maximum luminance occurs substantially within a middle range of said predetermined color temperature range.

21. A computer readable medium having instructions stored thereon that when executed by a processor implement a method of selecting light source candidates for an illumination system, said illumination system being white-balance adjustable over a predetermined color temperature range, the method comprising the steps of:

(a) varying a percentage composition of red, green and blue phosphors to generate a first set and a second set of light source candidates;

(b) from said first set and said second set, selecting a plurality of candidate pairs;

(c) calculating combined luminance spectrums for one candidate pair of the plurality of candidate pairs thereof;

across various brightness levels of said light sources candidates;

(d) from said combined luminance spectrums, calculating a color temperature-luminance relationship for said candidate pair; and

(e) rejecting said candidate pair unless said color temperature-luminance relationship satisfies a predefined selection criterion.

22. The computer readable medium according to claim 21 wherein said method further comprises the steps of:

(f) from said combined luminance spectrums, calculating a chromaticity relationship for said candidate pair; and

(g) rejecting said pair unless said chromaticity relationship satisfies said predefined selection criterion.

23. The computer readable medium according to claim 21 wherein said method further comprises the step of:

repeating said steps (c) to (e) for other candidate pairs of the plurality, of candidate pairs.

24. The computer readable medium according to claim 21 wherein said step (e) of said method further comprises the steps of:

analyzing said luminance-color temperature relationship; and

rejecting said candidate pair unless a predetermined luminance threshold is reached across said predetermined color temperature range.

25. The computer readable medium according to claim 24 wherein said predetermined luminance threshold is 70% of a maximum luminance value of said candidate pair.

26. The computer readable medium according to claim 21 wherein said predetermined color temperature range comprises a lower color temperature value of 5,000 K and a higher color temperature value of 6,500 K.

27. The computer readable medium according to claim 22 wherein said step (f) of said method further comprises the steps of:

analyzing said chromaticity relationship;

comparing said chromaticity relationship to a CIE black body radiation curve over said color temperature range; and

rejecting said candidate pair unless said chromaticity relationship is similar to said CIE black body radiation curve.

28. The computer readable medium according to claim 21 wherein said step (e) of said method further comprises the steps of:

analyzing said luminance-color temperature relationship; and

rejecting said candidate pair unless a maximum luminance occurs substantially within a middle range of said predetermined color temperature range.