Method and apparatus to minimize lamp flicker and increase contrast ratio in projection devices

• US 20060139532A1
• Filed: 08/25/2005
• Published: 06/29/2006
• Est. Priority Date: 12/16/2004
• Status: Active Grant

• Current Assignee: Lightmaster Systems Incorporated
• Original Assignee: Lightmaster Systems Incorporated
• Inventors: Berman, Arthur
• Granted Patent: US 7,570,240 B2
• Time in Patent Office: Days
• US Class Current: 349/117
• CPC Class Codes: G02B 27/281 used for attenuating light intensity, e.g. comprising rotatable polarising elements
• CPC Class Codes: G02F 1/13362 providing polarized light, e.g. by converting a polarisation component into another one
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/136277 formed on a semiconductor substrate, e.g. of silicon
• CPC Class Codes: H04N 5/7441 the modulator being an array of liquid crystal cells
• CPC Class Codes: H04N 9/3105 for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10
• CPC Class Codes: H04N 9/3155 for controlling the light source light source control per se H05B35/00 – H05B47/00; control of an illumination source for displays in general G09G3/3406

Abstract

A variable retarder is inserted in a polarized light beam. The retardance of the variable retarder is increased when the light beam increases in brightness and is decreased when the light beam decreases in brightness. The amount of increase and/or decrease in retardance is calculated to stabilize the brightness of the light beam. The variable retarder may be used in conjunction with an auto-iris and share a same brightness detector.

Claims

1. A device, comprising:

a driver device coupled to the sensor and the variable retarder;

wherein the device driver is configured to drive the variable retarder to varying states of retardation based on a brightness sensed by the sensor.

2. The device according to claim 1, wherein the sensor comprises a photo sensor.

3. The device according to claim 1, wherein the sensor and the variable retarder are disposed in at least one light path of a video projection device.

4. The device according to claim 3, wherein the video projection device comprises a Liquid Crystal on Silicon (LCOS) High Definition (HD) Television.

5. The device according to claim 3, wherein the variable retarder is disposed upstream of a linear polarizer in an input light path of a kernel of the video projection device.

6. The device according to claim 5, wherein the kernel is a Liquid Crystal on Silicon (LCOS) based kernel.

7. The device according to claim 1, wherein:

the sensor comprises a video card comprising an image brightness circuit that detects brightness of an image; and

the driver device is configured to drive a retardation state of the variable retarder relative to the detected brightness.

9. The device according to claim 7, wherein the variable retarder is disposed upstream of a linear polarizer in a light path.

10. The device according to claim 1, wherein the variable retarder comprises an inorganic alignment material aligned relative to an axis of polarization of an input light having a brightness sensed by the sensor.

11. The device according to claim 1, wherein:

the device driver is further configured to drive the variable retarder to varying states of retardation based simultaneously on both the brightness sensed by the sensor and a brightness of a video image.

12. The device according to claim 11, wherein the brightness sensed by the sensor comprises the brightness of a light in which the video image is modulated or to be modulated.

8. The device according to claim 8, wherein driver device is configured to increase the retardation of the variable retarder for low levels of detected brightness compared to higher levels of detected brightness.

13. A light stabilizer comprising a variable retarder set up to increase and decrease an amount of retardation exhibited by the variable retarder based on respective increases and decreases of a light source.

14. The light stabilizer according to claim 13, wherein the variable retarder comprises, a liquid crystal material sandwiched between transparent substrates and having electrodes for applying an electric field to effect the increases and decreases in retardation.

15. The light stabilizer according to claim 13, wherien the variable retarder is positioned upstream of a linear polarizer in a polarized light path.

16. A device, comprising:

Means for detecting a light level;

Means for adjusting a retardance value based on the detected light level;

wherein the retardance value comprises an energization state of a liquid crystal retarder.

17. The device according to claim 16, wherein the means for detecting a light level comprises a photo detector.

18. The device according to claim 16, wherein the means for detecting a light level comprises means for detecting a brightness level in a video image.

19. The device according to claim 16, wherein:

the means for detecting a light level comprises means for detecting a brightness level of a lamp in a video projection system combined with means for detecting a brightness level in a video image;

the means for adjusting comprises,

means to adjust the retarder to decrease an amount of light input to the video projection system when the brightness level of the video image is dark, and

means to adjust the retarder to decrease an amount of light input to the video projector system when the brightness level of the lamp exceeds a predetermined brightness level.

20. The device according to claim 19, wherein the retarder comprises a variable retarder upstream of a linear polarizer in an input light path of the video projection system.

21. The device according to claim 19, wherein the retarder comprises an inorganic alignment material with a tilted homeotropic alignment and a liquid crystal material with a negative dielectric anisotropy.

22. The device according to claim 19, wherein:

the retarder is upstream of a linear polarizer in an input light path of the projection system; and

the alignment material is aligned at an angle of approximately 45 degrees to an axis of linear polarization of the input light path.

23. A method comprising the step of:

adjusting a brightness of an light beam based on and relative to a brightness of a lamp providing light for the input light beam and a brightness of a video image to be modulated into the light beam.

24. The method according to claim 23, wherein the light beam is a linearly polarized light beam and the step of adjusting a brightness of the light beam comprises adjusting a retardance of a variable retarder upstream of a linear polarizer in the light beam.

25. The method according to claim 24, wherein:

the step of adjusting the retardance comprises,

adjusting the retarder to decrease an amount of light in the light beam when the brightness level of a video image to be modulated into the light beam is below a predetermined threshold, and

adjusting the retarder to decrease an amount of light input to the video projector system when a brightness level of the lamp exceeds a predetermined brightness level.