Patent ID: 8089578

Claim:
A surface light source device comprising: a point source of light; and a light guide plate causing light of the point source of light to be introduced from a light incident surface and be emitted from a light emission surface to outside, wherein the point source of light is provided at a position facing the light incident surface of the light guide plate, wherein the light guide plate includes a light introducing unit for trapping light from the point source of light entering from the light incident surface, and a light guide plate body having a thickness smaller than a maximum thickness of a light introducing unit, being provided so as to be continuous to the light introducing unit, and causing the trapped light to be emitted from the light emission surface to outside by light emitting means, wherein the light introducing unit comprises a first inclined surface on a surface of the light guide plate on a light emission side or a surface opposite thereto, the first inclined surface being inclined from a surface of a portion having a thickness larger than that of the light guide plate body toward an end of a surface of the light guide plate body, wherein the light introducing unit comprises a second inclined surface having an angle of inclination smaller than that of the first inclined surface, the second inclined surface being provided on at least one of a side closer to the point source of light than the first inclined surface and a side more distant from the point source of light than the first inclined surface, and wherein the light introducing unit comprises a directivity conversion pattern on a surface of the light guide plate body on a light emission side or a surface opposite thereto, the directivity conversion pattern formed of patterns extending in a radial direction and centering near the point source of light, the pattern for converting a directivity spread of light entering the light introducing unit in a thickness direction of the light guide plate to a directivity characteristic inclined toward a direction parallel to a surface direction of the light guide plate.