LED backlight and liquid crystal display device using thereof

• US 20070253216A1
• Filed: 04/16/2007
• Published: 11/01/2007
• Est. Priority Date: 04/28/2006
• Status: Active Grant

• Current Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Original Assignee: Hitachi Display Devices Limited (Hitachi, Ltd.), Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Watanabe, Saburo
• Granted Patent: US 7,905,613 B2
• Time in Patent Office: Days
• US Class Current: 362/601
• CPC Class Codes: G02B 6/0028 Light guide, e.g. taper
• 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 6/0061 to provide homogeneous light output intensity
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources

Abstract

An object of the present invention is to improve the color reproduction capability of a liquid crystal display backlight using white LEDs.

A backlight of the present invention includes: a light guide plate 6; a light diffusing optical waveguide 3 disposed adjacent the light guide plate 6; a plurality of white LEDs 1 disposed on the light diffusing optical waveguide 3; and single color LEDs (red LEDs) 2 disposed on respective opposite sides of the light diffusing optical waveguide 3; wherein light from the white LEDs 1 passes through the light diffusing optical waveguide 3 and enters the light guide plate 6 through a side thereof, whereas light from the single color LEDs 2 is diffused by the light diffusing optical waveguide 3 before entering the light guide plate 6 through the same side thereof. Thus, the light diffusing optical waveguide 3 mixes light from the white LEDs 1 and single color LEDs 2, resulting in improved color reproduction capability of the backlight.

Claims

1. A backlight comprising:

a light guide plate;

a light diffusing optical waveguide disposed adjacent said light guide plate;

a white LED disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said white LED and said light guide plate, said white LED emitting light toward a side of said light guide plate; and

a single color LED disposed on a different side of said light diffusing optical waveguide than said white LED.

2. The backlight as claimed in claim 1, wherein said single color LED is a red LED.

3. The backlight as claimed in claim 1, wherein said single color LED is disposed to increase the light intensity of said backlight at wavelengths around 620 nm.

4. The backlight as claimed in claim 1, wherein said light diffusing optical waveguide has white dots printed on the side thereof on which said white LED is disposed, said white dots constituting a light diffusing portion.

5. The backlight as claimed in claim 1, wherein said light diffusing optical waveguide has grooves formed in a side thereof facing said light guide plate, said grooves constituting a light diffusing portion.

6. The backlight as claimed in claim 4, wherein said white dots printed on said light diffusing optical waveguide are spaced more closely at a center portion of said light diffusing optical waveguide than at said different side of said light diffusing optical waveguide.

7. The backlight as claimed in claim 5, wherein said grooves formed on said light diffusing optical waveguide are spaced more closely at a center portion of said light diffusing optical waveguide than at said different side (or the single color LED side) of said light diffusing optical waveguide.

8. A liquid crystal display device comprising:

a white LED backlight; and

a display panel for controlling light from said backlight to display an image;

wherein said backlight comprises;

a light guide plate;

a light diffusing optical waveguide disposed adjacent said light guide plate;

a white LED disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said white LED and said light guide plate, said white LED emitting light toward a side of said light guide plate; and

a single color LED disposed on a different side of said light diffusing optical waveguide than said white LED.

9. The liquid crystal display device as claimed in claim 8, wherein:

light from said white LED passes through said light diffusing optical waveguide to enter said light guide plate;

light from said single color LED is diffused by said light diffusing optical waveguide before entering said light guide plate; and

said display panel controls light from said light guide plate to display said image.

10. The liquid crystal display device as claimed in claim 8, wherein said single color LED is a red LED.

11. The liquid crystal display device as claimed in claim 8, wherein said light diffusing optical waveguide has white dots printed on the side thereof on which said white LED is disposed, said white dots constituting a light diffusing portion.

12. The liquid crystal display device as claimed in claim 8, wherein said light diffusing optical waveguide has grooves formed in a side thereof facing said light guide plate, said grooves constituting a light diffusing portion.

13. A backlight comprising:

a light guide plate;

a light diffusing optical waveguide disposed adjacent said light guide plate;

a white LED disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said white LED and said light guide plate, said white LED emitting light toward a side of said light guide plate;

a single color LED disposed on a different side of said light diffusing optical waveguide than said white LED; and

a metal substrate having reflective properties;

wherein said light diffusing optical waveguide, said white LED, and said single color LED are formed on said reflective metal substrate.

14. The backlight as claimed in claim 13, wherein said light guide plate is formed on said reflective metal substrate.

15. The backlight as claimed in claim 13, wherein said reflective metal substrate provides heat dissipation from said white LED or said single color LED.

16. A liquid crystal display device comprising:

a white LED backlight; and

a display panel for controlling light from said backlight to display an image;

wherein said backlight comprises;

a light guide plate;

a light diffusing optical waveguide disposed adjacent said light guide plate;

a white LED disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said white LED and said light guide plate, said white LED emitting light toward a side of said light guide plate;

a single color LED disposed on a different side of said light diffusing optical waveguide than said white LED; and

a metal substrate having reflective properties; and

wherein said light diffusing optical waveguide, said white LED, and said single color LED are formed on said reflective metal substrate.

17. The liquid crystal display device as claimed in claim 16, wherein said light guide plate is formed on said reflective metal substrate.

18. The liquid crystal display device as claimed in claim 16, wherein said reflective metal substrate provides heat dissipation from said white LED or said single color LED.