Planar light source unit and display device

• US 20040109244A1
• Filed: 08/28/2003
• Published: 06/10/2004
• Est. Priority Date: 12/04/2002
• Status: Active Grant

• Current Assignee: Mitsubishi Electric Corporation
• Original Assignee: Advanced Display Technologies
• Inventors: Kokogawa, Toru
• Granted Patent: US 6,991,358 B2
• Time in Patent Office: Days
• US Class Current: 359/831
• CPC Class Codes: G02B 5/1866 Transmission gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials G02B5/1809, G02B5/1828, G02B5/1833, G02B5/1838 and G02B5/1847 take precedence
• CPC Class Codes: G02B 6/0036 2-D arrangement of prisms, protrusions, indentations or roughened surfaces
• 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 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer

Abstract

A light guide plate has a hologram pattern on a light exit surface. The hologram pattern anisotropically diffuses light in the direction parallel with a light incident surface of the light guide plate. On a back surface of the light guide plate are formed mirror-polished prism structures extending parallel with the light incident surface. A downward-pointing prism sheet with a given prism apex angle is placed on the light exit surface of the light guide plate. The use of the downward-pointing prism sheet together with the light guide plate having the anisotropic diffusion hologram pattern integrally formed thereon produces a liquid crystal display device with enhanced luminance properties.

Claims

1. A planar light source unit comprising:

a light source;

a light guide plate having a light incident surface through which light from the light source enters, a light exit surface through which light exits, and an anisotropic diffraction grating formed on the light exit surface or a surface opposite to the light exit surface for diffusing light in a principal diffusing direction along the light incident surface; and

a prism sheet for collecting light traveling from the light incident surface to an opposite side surface, having a plurality of prism structures on a surface opposite to the light exit surface, each of the plurality of prism structures having an apex angle of larger than 65 degrees and smaller than 68 degrees.

2. A planar light source unit according to claim 1, wherein the anisotropic diffraction grating comprises a hologram pattern integrally formed on the light guide plate.

3. A planar light source unit according to claim 1, wherein an apex angle of each of the plurality of prism structures is 66 degrees.

4. A planar light source unit according to claim 2, wherein an apex angle of each of the plurality of prism structures is 66 degrees.

5. A planar light source unit according to claim 1, wherein the anisotropic diffraction grating does not substantially diffuse light in a direction perpendicular to the principal diffusion direction.

6. A planar light source unit according to claim 1, wherein the light guide plate has smooth prism structures on a surface opposite to a surface where the anisotropic diffraction grating is formed for controlling an emission angle of light exiting through the light exit surface.

7. A planar light source unit according to claim 2, wherein the light guide plate has smooth prism structures on a surface opposite to a surface where the anisotropic diffraction grating is formed for controlling an emission angle of light exiting through the light exit surface.

8. A planar light source unit according to claim 1, wherein the prism sheet is directly placed on the light exit surface.

9. A planar light source unit according to claim 2, wherein the prism sheet is directly placed on the light exit surface.

10. A display device, comprising:

a planar light source unit; and

a display panel displaying images by controlling transmission of light from the planar light source unit;

the planar light source unit comprising;

a light source;

a light guide plate having a light incident surface through which light from the light source enters, a light exit surface through which light exits, and an anisotropic diffraction grating formed on the light exit surface or a surface opposite to the light exit surface for diffusing light in a principal diffusing direction along the light incident surface; and

a prism sheet for collecting light traveling from the light incident surface to an opposite side surface, having a plurality of prism structures on a surface opposite to the light exit surface, each of the plurality of prism structures having an apex angle of larger than 65 degrees and smaller than 68 degrees.