Light scattering and guiding light source device and liquid crystal display

• US 5,993,020 A
• Filed: 05/16/1997
• Issued: 11/30/1999
• Est. Priority Date: 07/23/1993
• Status: Expired due to Term

• Current Assignee: Nitto Jushi Kogyo Kabushiki Kaisha
• Original Assignee: Nitto Jushi Kogyo Kabushiki Kaisha
• Inventors: Koike, Yasuhiro
• Primary Examiner(s): TSO, LAURA K
• Application Number:
  US08/857,541
• Time in Patent Office: 928 Days
• Field of Search: 362/26, 362/31, 362/330
• US Class Current: 362/628
• CPC Class Codes: G02B 6/0016 Grooves, prisms, gratings, scattering particles or rough surfaces
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• 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 6/0041 provided in the bulk of the light guide
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02F 1/133615 Edge-illuminating devices, i.e. illuminating from the side

Abstract

A light scattering and guiding light source device which is capable of providing a uniform illumination light, simple structure and low cost. A wedge-shaped light scattering guide has an incident surface for introducing light rays from a fluorescent lamp. The directions of the rays are changed by scattering. The rays propagate through the body while reflected repeatedly. Parts of the rays go outwards at plural reflective points. The angle of reflection increases successively, thus increasing the possibility that the light exits from the exit surface. This effect cancels another effect that portions close to the light source shines strongly. Both effects are balanced to make uniform the brightness over the exit surface. Reflective sheets are disposed along the inclined surface and around the fluorescent lamp to keep the brightness high. A prismatic exit direction modifier giving on the light exit surface is employed to modify the light exit direction characteristic. The light source device is mounted on a liquid crystal display as a backlight source to provide an improved display quality.

Claims

1. A light scattering and guiding light source device comprising:

a light source element; and

a light scattering guide having a wedge shape, a light incident surface for receiving light from the light source element, a light exit surface and an inclined surface, the light incident surface being at a thick end of the wedge shape such that the thickness of the light scattering guide decreases with increasing distance from the light incident surface,

the light exit surface and the inclined surface extending from the light incident surface with the inclined surface being inclined with respect to the light exit surface,

the light scattering guide having a uniform scattering power greater than zero inside to provide three dimensional scattering to light travelling through the light scattering guide such that light received from the light source element at the light incident surface is emitted uniformly from the light exit surface.

2. A light scattering and guiding light source device as claimed in claim 1, further comprising a light exit direction modifying element provided along the light exit surface to modify a travelling direction of the light emitted from the light exit surface so that the light will travel in a direction generally perpendicular to the light exit surface.

3. A light scattering and guiding light source device according to claim 2, wherein the light exit modifying element is provided as a unitary structure with the light scattering guide.

4. A light scattering and guiding light source device as claimed in claim 2, wherein the light exit direction modifying element is provided as a separate structure from the light scattering guide.

5. A liquid crystal display device, comprising:

a light source element;

a light scattering guide having a wedge shape, a light incident surface for receiving light from the light source element, a light exit surface and an inclined surface, the light incident surface being at a thick end of the wedge shape such that the thickness of the light scattering guide decreases with increasing distance from the light incident surface, the light exit surface and the inclined surface extending from the light incident surface with the inclined surface being inclined with respect to the light exit surface, the light scattering guide having a uniform scattering power greater than zero inside to provide three dimensional scattering to light travelling through the light scattering guide such that light received from the light source element at the light incident surface is emitted uniformly from the light exit surface; and

a liquid crystal display provided adjacent to the light exit surface of the light scattering guide to receive backlighting from the light emitted from the light exit surface.

6. A liquid crystal display device according to claim 5, further comprising a light exit direction modifying element provided along the light exit surface to modify a travelling direction of the light emitted from the light exit surface so that the light will travel in a direction generally perpendicular to the light exit surface.

7. A liquid crystal display device according to claim 6, wherein the light exit modifying element is provided as a unitary structure with the light scattering guide.

8. A liquid crystal display device according to claim 6, wherein the light exit direction modifying element is provided as a separate structure from the light scattering guide.