Surface light source device of side light type

• US 5,810,464 A
• Filed: 02/01/1996
• Issued: 09/22/1998
• Est. Priority Date: 02/03/1995
• Status: Expired due to Fees

• Current Assignee: Enplas Corporation
• Original Assignee: Enplas Corporation, Yasuhiro Koike
• Inventors: Yokoyama, Kazuaki, Ishikawa, Tsuyoshi, Watai, Kayoko
• Primary Examiner(s): CARIASO, ALAN B
• Application Number:
  US08/595,503
• Time in Patent Office: 964 Days
• Field of Search: 362/31, 362/330, 362/26, 362/27, 362/268, 362/327, 362/328, 362/331, 349/65, 349/70, 349/64, 349/67, 385/146
• US Class Current: 362/620
• CPC Class Codes: G02B 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0053 Prismatic sheet or layer; Brightness enhancement element, sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer

Abstract

A surface light source device of side light type controls the intensity of light rays emitted therefrom. The surface light source device of side light type comprises a light scattering guide 20 having a light incidence surface 22, a light emission surface 23 and an inclined surface 25. The device further includes a primary light source L arranged around one side of the light incidence surface 22, a silver foil R surrounding the primary light source L, a prism sheet 4 arranged along the light emission surface 23, and a silver foil S arranged along the inclined surface 25. The inclined surface 25 of the light scattering guide 20 composed of three sections I, II and III. The section I is a convex cylindrical surface section having a radius of curvature of 330 mm. The tangential direction at the end of the guide on the side of the light incidence surface 22 is parallel to the light emission surface 23. The tangential direction at the boundary between the sections I and II is inclined at an angle 4° with respect to the light emission surface 23. The sections II and III are straight sections whose inclinations are 4° and 3.6° with respect to the light emission surface 23, respectively. The distribution of emitted light intensity from the surface light source device has a higher luminance around its center. Various distributions of emitted light intensity are provided by varying the transition of inclinations of the inclined surface (particularly refer to FIG. 13).

Claims

1. A surface light source device of side light type including a plate-shaped light scattering guide having a volumetrically uniform scattering power, and at least one primary light source arranged around one side of said light scattering guide,

said light scattering guide including a light incidence surface for admitting light rays supplied from said primary light source, a flat light emission surface for emitting light rays from said light scattering guide and an inclined surface on an opposite side from said light emission surface, wherein

said inclined surface has inclinations distributed depending on a distance from said light incidence surface in a manner such that a distribution of said inclinations is defined individually for a plurality of sections including a convex section near said light incidence surface and straight inclined sections around a central portion of said inclined surface so that intensities of light rays emitted from said light emission surface are the largest around an area corresponding to said central portion.

2. The surface light source device of side light type as set forth in claim 1, wherein said inclinations around boundaries of said sections are smoothly changed.

3. The surface light source device of side light type as set forth in claim 1, wherein said device further comprises a prism sheet disposed along said light emission surface for modifying propagation directions of said light rays emitted from said light emission surface.

4. The surface light source device of side light type as set forth in claim 2, wherein said device further comprises a prism sheet disposed along said light emission surface to modify propagation directions of said light rays emitted from said light emission surface.

5. The surface light source device of side light type as set forth in claim 1, wherein said device further comprises a reflector disposed along said inclined surface.

6. The surface light source device of side light type as set forth in claim 2, wherein said device further comprises a reflector disposed along said inclined surface.

7. The surface light source device of side light type as set forth in claim 3, wherein said device further comprises a reflector disposed along said inclined surface.

8. The surface light source device of said light type as set forth in claim 4, wherein said device further comprises a reflector disposed along said inclined surface.