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

• US 7,570,240 B2
• Filed: 08/25/2005
• Issued: 08/04/2009
• Est. Priority Date: 12/16/2004
• Status: Expired due to Fees

• Current Assignee: Lightmaster Systems Incorporated
• Original Assignee: Lightmaster Systems Incorporated
• Inventors: Berman, Arthur
• Primary Examiner(s): Hjerpe; Richard
• Assistant Examiner(s): Sheng; Tom V
• Application Number:
  US11/213,153
• Publication Number:
  US 20060139532A1
• Time in Patent Office: 1,440 Days
• Field of Search: 345/87, 345/102, 345/207, 349/5, 353/20, 353/37, 353/81, 353/82, 353/122, 359/20, 359/455, 359/634, 252/299.1, 252/582
• US Class Current: 345/87
• 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 a sensor and a variable retarder wherein the variable retarder comprises an inorganic alignment material with a tilted homeotropic alignment and a liquid crystal material with a negative dielectric anisotropy;

wherein the device driver is configured to drive the variable retarder to varying states of retardation based on a brightness level of a lamp sensed by the sensor and a brightness level in a video image;

wherein the retarder is configured to decrease an amount of light output by the lamp when the brightness level of the video image is dark;

wherein the retarder is configured to decrease an amount of light output by the lamp when the brightness level of the lamp exceeds a predetermined brightness level; and

wherein the variable retarder is disposed in an output light path of the lamp.

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.

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

9. 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.

10. The device according to claim 1, 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.

11. 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;

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 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.

12. The device according to claim 11, wherein the means for detecting a light level comprises a photo detector.

13. The device according to claim 11, wherein the means for detecting a light level comprises means for detecting a brightness level in a video image.

14. 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;

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, wherein the retarder comprises an inorganic alignment material with a tilted homeotropic alignment and a liquid crystal material with a negative dielectric anisotropy.

15. A method comprising:

adjusting a brightness of a 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 onto the light beam, wherein the light beam is a linearly polarized light beam and wherein adjusting the brightness of the light beam includes adjusting a retardance of a variable retarder upstream of a linear polarizer in the light beam; and

wherein adjusting the retardance of the variable retarder includes;

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

16. A device, comprising:

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

wherein the device driver is configured to drive the variable retarder to varying states of retardation based on a brightness level of a lamp sensed by the sensor and a brightness level in a video image;

wherein the retarder is configured to decrease an amount of light output by the lamp when the brightness level of the video image is dark;

wherein the retarder is configured to decrease an amount of light output by the lamp when the brightness level of the lamp exceeds a predetermined brightness level; and

wherein the variable retarder is disposed in an output light path of the lamp wherein the variable 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.