LED backlight and liquid crystal display device using thereof

• US 7,905,613 B2
• Filed: 04/16/2007
• Issued: 03/15/2011
• Est. Priority Date: 04/28/2006
• Status: Expired due to Fees

• 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
• Primary Examiner(s): Lee; Jong-Suk (James)
• Assistant Examiner(s): Tsidulko; Mark
• Application Number:
  US11/785,212
• Publication Number:
  US 20070253216A1
• Time in Patent Office: 1,429 Days
• Field of Search: 362/26, 362/27, 362/600, 362/601, 362606-608, 362/610, 362/612, 362/613, 362/615, 349/62, 349/65, 405/44, 405/46, 385/901, 385/902, 385/140, 385/129, 385/120, 385/15
• US Class Current: 362/26
• 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 plurality of white LEDs disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said plurality of white LEDs and said light guide plate, said plurality of white LEDs emitting a white light that propagates through the light diffusing optical wave guide toward a side of said light guide plate;

a single color LED disposed on a different side of said light diffusing optical waveguide than a side of said light diffusing optical waveguide on which said plurality of white LEDs are disposed, said single color LED emitting a single color light that propagates through said light diffusing optical waveguide to said light guide plate; and

a light diffusing portion disposed on a portion of said light diffusing optical waveguide where the plurality of white LEDs are not disposed for diffusing the single color light as the single color light propagates through said light diffusing optical waveguide,

wherein the single color light from the single color LED is directed to turn into the light guide plate at the light diffusing portion disposed on said light diffusing optical waveguide,

wherein the portion of said light diffusing optical waveguide on which said light diffusing portion is disposed does not oppose the side of said light diffusing optical waveguide on which the white LEDs are disposed, and

wherein said light diffusing optical waveguide has grooves formed in a side thereof facing said light guide plate, said grooves being spaced more closely at a center portion of said light diffusing optical waveguide than at the side on which the single color LED is disposed.

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 portion of said light diffusing optical waveguide has white dots printed on a side thereof on which said plurality of white LEDs are disposed, said white dots constituting said light diffusing portion.

5. 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.

6. 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 plurality of white LEDs disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said plurality of white LEDs and said light guide plate, said plurality of white LEDs emitting a white light that propagates through the light diffusing optical wave guide toward a side of said light guide plate;

a single color LED disposed on a different side of said light diffusing optical waveguide than a side of said light diffusing optical waveguide on which said plurality of white LEDs are disposed, said single color LED emitting a single color light that propagates through said light diffusing optical waveguide to said light guide plate; and

a light diffusing portion disposed on a portion of said light diffusing optical waveguide where the plurality of white LEDs are not disposed for diffusing the single color light as the single color light propagates through said light diffusing optical waveguide,

wherein the single color light from the single color LED is directed to turn into the light guide plate at the light diffusing portion disposed on said light diffusing optical waveguide,

wherein the portion of said light diffusing optical waveguide on which said light diffusing portion is disposed does not oppose the side of said light diffusing optical waveguide on which the white LEDs are disposed, and

wherein said light diffusing optical waveguide has grooves formed in a side thereof facing said light guide plate, said grooves being spaced more closely at a center portion of said light diffusing optical waveguide than at the side on which the single color LED is disposed.

7. The liquid crystal display device as claimed in claim 6, wherein:

the white light from said plurality of white LEDs propagates through said light diffusing optical waveguide to then enter said light guide plate;

the single color light from said single color LED is diffused by said light diffusing portion as the single color light propagates through said light diffusing optical waveguide and the single color light enters said light guide plate; and

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

8. The liquid crystal display device as claimed in claim 6, wherein said single color LED is a red LED.

9. The liquid crystal display device as claimed in claim 6, wherein said light diffusing portion of said light diffusing optical waveguide has white dots printed on a side thereof on which said plurality of white LEDs are disposed, said white dots constituting said light diffusing portion.

10. A backlight comprising:

a light guide plate;

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

a plurality of white LEDs disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said plurality of white LEDs and said light guide plate, said plurality of white LEDs emitting a white light that propagates through the light diffusing optical wave guide toward a side of said light guide plate;

a single color LED disposed on a different side of said light diffusing optical waveguide than a side of said light diffusing optical waveguide on which said plurality of white LEDs are disposed, said single color LED emitting a single color light that propagates through said light diffusing optical waveguide to said light guide plate; and

a metal substrate having reflective properties;

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

wherein a light diffusing portion is disposed on a portion of said light diffusing optical waveguide where the plurality of white LEDs are not disposed for diffusing the single color light as the single color light propagates through said light diffusing optical waveguide,

wherein the single color light from the single color LED is directed to turn into the light guide plate at the light diffusing portion disposed on said light diffusing optical waveguide,

wherein the portion of said light diffusing optical waveguide on which said light diffusing portion is disposed does not oppose the side of said light diffusing optical waveguide on which the white LEDs are disposed, and

wherein said light diffusing optical waveguide has grooves formed in a side thereof facing said light guide plate, said grooves being spaced more closely at a center portion of said light diffusing optical waveguide than at the side on which the single color LED is disposed.

11. The backlight as claimed in claim 10, wherein said light guide plate is formed on said reflective metal substrate.

12. The backlight as claimed in claim 10, wherein said reflective metal substrate provides heat dissipation from said plurality of white LEDs or said single color LED.

13. 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 plurality of white LEDs disposed on said light diffusing optical waveguide such that said light diffusing optical waveguide is sandwiched between said plurality of white LEDs and said light guide plate, said plurality of white LEDs emitting a white light that propagates through the light diffusing optical wave guide toward a side of said light guide plate;

a single color LED disposed on a different side of said light diffusing optical waveguide than a side of said light diffusing optical waveguide on which said plurality of white LEDs are disposed, said single color LED emitting a single color light that propagates through said light diffusing optical waveguide to said light guide plate; and

a metal substrate having reflective properties;

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

wherein a light diffusing portion is disposed on a portion of said light diffusing optical waveguide where the plurality of white LEDs are not disposed for diffusing the single color light as the single color light propagates through said light diffusing optical waveguide,

wherein the single color light from the single color LED is directed to turn into the light guide plate at the light diffusing portion disposed on said light diffusing optical waveguide, and

wherein the portion of said light diffusing optical waveguide on which said light diffusing portion is disposed does not oppose the side of said light diffusing optical waveguide on which the white LEDs are disposed, and

wherein said light diffusing optical waveguide has grooves formed in a side thereof facing said light guide plate, said grooves being spaced more closely at a center portion of said light diffusing optical waveguide than at the side on which the single color LED is disposed.

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

15. The liquid crystal display device as claimed in claim 13, wherein said reflective metal substrate provides heat dissipation from said plurality of white LEDs or said single color LED.