Surface light source device and liquid crystal display

• US 5,887,964 A
• Filed: 06/09/1997
• Issued: 03/30/1999
• Est. Priority Date: 08/01/1995
• Status: Expired due to Term

• Current Assignee: Nitto Jushi Kogyo Kabushiki Kaisha
• Original Assignee: Nitto Jushi Kogyo Kabushiki Kaisha, Yasuhiro Koike
• Inventors: Koike, Yasuhiro, Higuchi, Eizaburo
• Primary Examiner(s): CARIASO, ALAN B
• Application Number:
  US08/809,890
• Time in Patent Office: 659 Days
• Field of Search: 362/26, 362/27, 362/31, 362/330, 362/333, 362/339, 349/64, 349/65, 349/66, 349/67
• US Class Current: 362/620
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer

Abstract

There is provided a surface light source device which is excellent in whiteness and softness of a luminant surface and able to retain reflective appearance from occurring. The surface light source device is effectively applied to back lighting in a liquid crystal display. A fluorescent lamp (L) is disposed in the vicinity of an incidence surface (2) of a light guide plate (1). A prism sheet (4'"'"') having prism surfaces formed on both surfaces is disposed along an exiting surface (5). The prism sheet (4'"'"') is oriented such that prism rows (4a, 4b) on the inside surface run in the transverse direction of the light guide plate (1) while prism rows (4c, 4d) on the outside surface run in the longitudinal direction of the light guide plate (1). A reflector (3) is disposed along a back surface (6) of the light guide plate (1). Light emitted from the exiting surface (5) is led to the frontal direction by the action of the prism rows (4a, 4b) and then returned toward the light guide plate (1) after having been shifted in the transverse direction by the prism rows (4c, 4d). The history of a path of light emitted from the prism sheet (4'"'"') is diversified through this process, thereby improving visual characteristics.

Claims

1. A surface light source device, comprising:

a light guide plate made of light scattering and guiding material,

a light source to supply light from at least one side direction of said light guide plate,

a reflector disposed along a back surface of said light guide plate, and

a prism sheet disposed along an exiting surface of said light guide plate,

wherein said prism sheet has as an outside prism surface and an inside prism surface respectively provided with a large number of prism rows;

the prism rows formed on said inside prism surface running in a direction perpendicular to a light supply direction from said light source while having a prism vertical angle such that light making propagation in a preferential propagation direction of luminous flux emitted from said light guide plate is led to around a frontal direction within said prism sheet; and

the prism rows formed on said outside prism surface running in a direction parallel to the light supply direction from said light source while having a prism vertical angle such that beams led to around the frontal direction within said prism sheet are returned toward said inside surface after having been shifted in a direction substantially perpendicular to said light supply direction.

2. A surface light source device according to claim 1, wherein said light guide plate has a wedge-shaped section and said light source is disposed along a end surface on a thick side of said light guide plate.

3. A surface light source device according to claim 1, wherein each prism vertical angle of the prism rows formed on said outside prism surface is about 90°

.

4. A surface light source device according to claim 1, wherein each prism vertical angle of the prism rows formed on said outside prism surface is in the range of 70°

to 130°

.

5. A liquid crystal display, comprising:

a liquid crystal panel, and

a surface light source device disposed to backlight said liquid crystal panel,

wherein said surface light source device includes a light guide plate made of light scattering and guiding material, a light source to supply light from at least one side direction of said light guide plate, a reflector disposed along a back surface of said light guide plates and a prism sheet disposed along an exiting surface of said light guide plate;

said prism sheet has as an outside prism surface and an inside prism surface respectively provided with a large number of prism rows;

the prism rows formed on said inside prism surface running in a direction perpendicular to a light supply direction from said light source while having such a prism vertical angle that light making propagation in a preferential propagation direction of luminous flux emitted from said light guide plate is led to around a frontal direction within said prism sheet; and

the prism rows formed on said outside prism surface running in a direction parallel to the light supply direction from said light source while having such a prism vertical angle that beams led to around the frontal direction within said prism sheet are returned toward said inside surface after having been shifted in a direction substantially perpendicular to said light supply direction.

6. A liquid crystal display according to claim 5, wherein said light guide plate has a wedge-shaped section, and said light source is disposed along a end surface on the thick side of said light guide plate.

7. A liquid crystal display according to claim 5, wherein each prism vertical angle of the prism rows formed on said outside prism surface is about 90°

.

8. A liquid crystal display according to claim 5, wherein each prism vertical angle of the prism rows formed on said outside prism surface is in the range of 70°

to 130°

.