Backlight for a color LCD

• US 20020167624A1
• Filed: 05/10/2001
• Published: 11/14/2002
• Est. Priority Date: 05/10/2001
• Status: Active Grant

• Current Assignee: Philips Lumileds Lighting Company LLC (Apollo Global Management, Inc.)
• Original Assignee: Lumileds Lighting US LLC (Apollo Global Management, Inc.)
• Inventors: Harbers, Gerard, Paolini, Steven, Snyder, Wayne L.
• Granted Patent: US 6,791,636 B2
• Time in Patent Office: Days
• US Class Current: 349/61
• CPC Class Codes: G02B 6/0038 Linear indentations or grooves, e.g. arc-shaped grooves or meandering grooves, extending over the full length or width of the light guide
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side
• CPC Class Codes: G02F 1/133617 Illumination with ultraviolet light; Luminescent elements or materials associated to the cell
• CPC Class Codes: G02F 1/133621 providing coloured light G02F1/133617, G02F1/133533 take precedence

Abstract

In one embodiment, a color, transmissive LCD uses red, green, and blue LEDs as the light source. The red LED is optically coupled to a first edge of a rectangular light guide; the green LED is optically coupled to a second edge of the light guide; and the blue LED is optically coupled to a third edge of the light guide. Three sets of deformities in the light guide selectively direct the R, G, and B light out of the front surface of the light guide. The R, G, and B LEDs are constantly on and there is no color filtering. In another embodiment, a blue light LED is optically coupled to one or more edges of a light guide, and phosphor strips are placed on a surface of the light guide coinciding with the red and green pixel columns. Deformities below the red and green phosphor strips and below the blue pixel areas direct blue light to the backs of the phosphor strips and to the blue pixel areas. If an ultraviolet light LED is used, phosphor strips for the blue pixel areas would also be used.

Claims

1. A device comprising:

a backlight for a color liquid crystal display, said backlight comprising;

at least one light guide having a first surface, an opposing second surface, and a plurality of edges;

at least one red light emitting diode (LED) optically coupled to a first edge of said light guide;

at least one green LED optically coupled to a second edge of said light guide; and

at least one blue LED optically coupled to a third edge of said light guide,

said light guide including light directing elements, a first set of light directing elements causing light entering said first edge to be directed to exit said first surface in areas corresponding to red pixels in said display, a second set of light directing elements causing light entering said second edge to be directed to exit said first surface in areas corresponding to green pixels in said display, and a third set of light directing elements causing light entering said third edge to be directed to exit said first surface in areas corresponding to blue pixels in said display.

2. The device of claim 1 further comprising:

a plurality of layers including a liquid crystal layer.

3. The device of claim 1 wherein said light directing elements are deformities in a surface of said light guide.

4. The device of claim 3 wherein said deformities include ridges in said light guide.

5. The device of claim 4 wherein,

said first set of light directing elements include ridges having angled surfaces for receiving light entering said first edge;

said second set of light directing elements include ridges having angled surfaces orthogonal to said angled surfaces of said first set of light directing elements surfaces for receiving light entering said second edge; and

said third set of light directing elements include ridges having angled surfaces orthogonal to said angled surfaces of said first set and said second set of light directing elements surfaces for receiving light entering said third edge.

6. The device of claim 1 wherein said light directing elements are positioned to cause light to leak out of said light guide only in areas corresponding to pixel positions.

7. The device of claim 1 wherein said light directing elements are arranged in columns to coincide with columns of pixels.

8. The device of claim 1 wherein said light guide includes lenses for collimating light exiting said light guide.

9. The device of claim 8 wherein there is one lens per pixel in said display.

10. The device of claim 1 further comprising a plurality of layers comprising:

a first polarizing filter;

an energizing array;

a liquid crystal layer; and

a second polarizing filter.

11. The device of claim 10 wherein said energizing array is a thin film transistor array.

12. The device of claim 10 wherein said plurality of layers lacks a color filter.

14. The method of claim 13 wherein said plurality of layers comprises a first polarizing filter, a thin film transistor array, said liquid crystal layer, and a second polarizing filter, said selectively controlling said crystal layer comprising:

selectively activating transistors in said thin film transistor array.

16. The device of claim 15 wherein said LED emits blue light.

17. The device of claim 15 further comprising third areas on said first surface of said light guide having a third phosphor material that, when irradiated by light emitted by said LED, generates a blue light.

18. The device of claim 17 wherein said LED emits ultraviolet light.

13. A method performed by a color liquid crystal display, said display comprising a plurality of layers including a liquid crystal layer and a backlight comprising at least one light guide having a first surface, an opposing second surface, and a plurality of edges;

at least one red light emitting diode (LED) optically coupled to a first edge of said light guide;

at least one green LED optically coupled to a second edge of said light guide; and

at least one blue LED optically coupled to a third edge of said light guide, said light guide including light directing elements, a first set of light directing elements causing light entering said first edge to be reflected to exit said first surface in areas corresponding to red pixels in said display, a second set of light directing elements causing light entering said second edge to be reflected to exit said first surface in areas corresponding to green pixels in said display, and a third set of light directing elements causing light entering said third edge to be reflected to exit said first surface in areas corresponding to blue pixels in said display, said method comprising;

energizing said red light emitting diode (LED) optically coupled to said first edge of said light guide;

energizing said green LED optically coupled to said second edge of said light guide;

energizing said blue LED optically coupled to said third edge of said light guide; and

selectively controlling said liquid crystal layer to display an image comprising a combination of red, green, and blue light.

15. A device comprising:

a backlight for a color liquid crystal display comprising;

at least one light guide having a first surface and an opposing second surface;

a light emitting diode (LED) emitting light having a wavelength equal to or less than blue light, said LED being optically coupled to said light guide;

a plurality of first areas on said first surface of said light guide having a first phosphor material that, when irradiated by light emitted by said LED, generate a red light;

a plurality of second areas on said first surface of said light guide having a second phosphor material that, when irradiated by light emitted by said LED, generate a green light; and

deformities formed in said light guide directing light from said LED toward said first surface, said red light and green light emitted by said first areas and said second areas coinciding with red and green pixels in said display.