Planar light source device and liquid crystal display device using the same

• US 6,976,779 B2
• Filed: 07/24/2003
• Issued: 12/20/2005
• Est. Priority Date: 07/26/2002
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Advanced Display Technologies, Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Ohtsuki, Hideyo, Nakanishi, Kunifumi, Yoneda, Toshiyuki
• Primary Examiner(s): Husar, Stephen
• Assistant Examiner(s): Han, Jason
• Application Number:
  US10/625,652
• Publication Number:
  US 20040109664A1
• Time in Patent Office: 880 Days
• Field of Search: 362 26- 27, 362/31, 362/234, 362/293, 362/555, 362/561, 362/601, 362/608, 362/612, 362/615, 362/621, 349/68
• US Class Current: 362/608
• CPC Class Codes: G02B 6/0001 specially adapted for lighting devices or systems lighting or signalling on vehicles using light guides B60Q1/00; lighting devices for vehicle dashboards B60Q3/10; lighting devices for vehicle interior using light guides B60Q3/62; lighting devices mounted on the vehicle rear part using light guides F21S43/235; measuring arrangements having light conducting pointers G01D13/265; illumination of liquid crystal displays G02F1/1336; illuminated signs G09F13/00
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces
• CPC Class Codes: G02B 6/0026 Wavelength selective element, sheet or layer, e.g. filter or grating

Abstract

The liquid crystal display device has red, green, and blue LEDs, each emitting a different color light, as a light source. An acrylic lens is mounted on the emission surface of the LED to change angular distributions of light from the LED. The shape of the acrylic lens varies depending on the color of the LED. The angular distribution of emitting light thereby differs by the color of LED to cancel out wavelength dependency of transmittance at each viewing direction in a liquid crystal panel.

Claims

1. A planar light source device, comprising:

a plurality of light sources each configured to emit different colors of light having different light emission angular distribution; and

a light guide plate configured to receive the different colors of light having the different light emission angular distribution from the plurality of light sources at a side face and to distribute the light over a surface thereof.

2. A planar light source device according to claim 1, comprising a refractor mounted on an emission surface of each of the plurality of light sources, each of the refractors being configured with a different shape for the different light sources and providing the different angular distribution for the different light sources.

3. A planar light source device according to claim 1, wherein the light emission angular distribution of a light source of the plurality of light sources emitting longer wavelength light is smaller than the light emission angular distribution of a light source of the plurality of light sources emitting shorter wavelength light.

4. A planar light source according to claim 1, wherein the plurality of light sources include red, green, and blue light emitting diodes.

5. A liquid crystal display device, comprising:

a planar light source device according to claim 1; and

a liquid crystal panel placed above an emission surface of the planar light source, the liquid crystal panel having two substrates with a liquid crystal layer interposed therebetween.

6. A liquid crystal display device according to claim 5, wherein the different light sources have different light emission angles in order that wavelength dependence of transmittance at a viewing direction in the liquid crystal panel is canceled out by wavelength dependence of luminance at the viewing direction in the planar light source device.

7. A planar light source device, comprising:

a plurality of light sources emitting different colors of light;

a light guide plate receiving light from the plurality of light sources at a side face to distribute the light over a surface thereof; and

a plurality of refractors, each of the refractors being configured to refract light from each of the plurality of light sources, wherein;

a shape of each of the refractors is different for each color of the plurality of light sources; and

a refraction angle of each of the refractors is different for each color of the plurality of light sources.

8. A planar light source device according to claim 7, wherein:

each of the refractors is formed on a side face of the light guide plate facing the plurality of light sources.

9. A planar light source device according to claim 7, further comprising a prism plate mounted between the plurality of light sources and the light guide plate, wherein:

each of the refractors is formed on a side face of the prism plate facing the plurality of light sources.

10. A planar light source device according to claim 7, wherein a refraction angle of the light source with longer wavelength light is smaller than a refraction angle of the light source with shorter wavelength light.

11. A planar light source device according to claim 7, wherein the plurality of light sources include red, green, and blue light emitting diodes.

12. A liquid crystal display device, comprising:

a planar light source device according to claim 7; and

a liquid crystal panel placed above an emission surface of the planar light source, the liquid crystal panel having two substrates with a liquid crystal layer interposed therebetween.

13. A liquid crystal display device according to claim 12, wherein the different refraction angles for different colors of light are provided in order that wavelength dependence of transmittance at a viewing direction in the liquid crystal panel is canceled out by wavelength dependence of luminance at the viewing direction in the planar light source device.

14. A liquid crystal display device, comprising:

a planar light source comprising a light source;

a light guide plate configured to receive light from the light source at a side face to distribute the light over a surface thereof, and a hologram configured to diffract light at different angles; and

a liquid crystal panel placed above an emission surface of the planar light source, the liquid crystal panel having two substrates with a liquid crystal layer interposed therebetween,

wherein the hologram is arranged in order that wavelength dependence of transmittance at a viewing direction in the liquid crystal panel is canceled out by wavelength dependence of luminance at the viewing direction in the planar light source device; and

wherein the hologram is placed between the light source and the light guide plate.

15. The liquid crystal display device according to claim 14, wherein the hologram diffracts longer wavelength light at an angle and diffracts shorter wavelength light at a larger angle than the angle of the longer wavelength light.