Light guide plate for point source

• US 6,196,691 B1
• Filed: 03/31/1999
• Issued: 03/06/2001
• Est. Priority Date: 04/01/1998
• Status: Expired due to Term

• Current Assignee: Shimada Precision, Co., Ltd.
• Original Assignee: Shimada Precision, Co., Ltd.
• Inventors: Ochiai, Shin-Ichiro
• Primary Examiner(s): Husar, Stephen
• Assistant Examiner(s): WARD, JOHN A
• Application Number:
  US09/282,182
• Time in Patent Office: 706 Days
• Field of Search: 362/26, 362/27, 362/28, 362/29, 362/30, 362/31, 362/555, 362/558, 362/560, 362/561, 349/65, 349/62, 349/112, 385/10
• US Class Current: 362/617
• 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 6/0046 Tapered light guide, e.g. wedge-shaped light guide
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources

Abstract

Rays of light from three light-emitting diodes 5 incident at a thicker side end edge 2c of a light guide plate 2 made of a transparent plate. A ratio of grating part width/non-grating part width in a unit width of a diffraction grating 3 provided on a rear surface 2b of the light guide plate 2 is varied, and grating constant of a diffraction grating 4 of a front surface 2a provided perpendicularly to the diffraction grating 3, is set to a fixed value smaller than a mean grating constant of the diffraction grating of the rear surface 2b, so that uniform, high brightness at the front surface 2a of the light guide plate 2 can be obtained. Therefore, the light guide plate can perform high, uniform brightness over a whole illuminating surface even with a point light source, and yet can prolong life of batteries by virtue of reduction in power consumption of the light source.

Claims

1. A light guide plate comprising:

a transparent plate; and

diffraction gratings provided on both rear and front surfaces of the plate and diffracting light incident from one or more point light sources at at least one end face of the plate;

wherein

a ratio of grating part width/non-grating part width in a unit width, or cross-sectional shape, of the diffraction grating of the rear surface is varied, and

the diffraction grating of the front surface is provided perpendicularly to the diffraction grating of the rear surface, while grating constant of the grating on the front surface is set to a fixed value smaller than a mean grating constant of the diffraction grating on the rear surface or the cross-sectional shape of the diffraction grating on the front surface is set to such a specified shape that high-order diffracted light is diffracted at high efficiency, whereby

uniform, high brightness at the front surface of the light guide plate can be obtained.

3. The light guide plate according to claim 1, wherein a diffusion plate for uniformizing diffracted light or turning any spectrally dispersed diffraction light back into white light through irregular reflection/refraction is provided on a front surface side of the light guide plate.

2. A light guide plate comprising:

a transparent plate; and

diffraction gratings provided on both rear and front surfaces of the plate and diffracting light incident from one or more point light sources at a rear surface of the plate;

wherein

the diffraction grating of the front surface and the diffraction grating of the rear surface are provided perpendicularly to each other, while grating constants of the diffraction gratings, or cross-sectional shapes of the diffraction gratings, are so set that uniform, high brightness at the front surface of the light guide plate can be obtained.

4. The light guide plate according to claim 2, wherein a diffusion plate for uniformizing diffracted light or turning any spectrally dispersed diffraction light back into white light through irregular reflection/refraction is provided on a front surface side of the light guide plate.