초록 ▼

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 va

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.

대표청구항 ▼

[What is claimed is:] [1.]a transparent plate; anddiffraction 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; whereina ratio of grating part width/non-grating part width in a uni

[What is claimed is:] [1.]a transparent plate; anddiffraction 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; whereina 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, andthe 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, wherebyuniform, high brightness at the front surface of the light guide plate can be obtained.