Light guide plate and surface light source using the light guide plate

Abstract

A light guide plate is provided including a first lens portion comprising a plurality of recessed or projected lenticular unit lenses formed of the same resin as that of the light guide plate on a light emission surface. The plurality of lenticular unit lenses in the first lens portion are triangular prism portions whose respective vertexes have an angle of 125.degree. to 165.degree. and are so arranged that their respective ridge lines are nearly parallel to each other. Such construction makes it possible to set the number of lenticular lens sheets used to one or to further eliminate the necessity of the lenticular lens sheets, so that the cost of parts and the fabrication cost of the light guide plate can be reduced. A second lens portion may be provided on a light reflective surface opposite to the light emission surface on which the first lens portion is disposed, the second lens portion including a plurality of recessed or projected lenticular unit lenses formed of the same resin as that of the light guide plate. Alternatively, a light guide plate is provided having a plurality of grooves with approximately equal groove widths formed on a surface opposite to a light emission surface, the grooves being arranged substantially parallel to each other and the spacing between the grooves narrowing as the distance from the light incident surface increases, with the spacing from the far end of one of the plurality of grooves proximate to the light incident surface to the near end of a groove adjacent thereto farther away from the light incident surface being 5 to 15 times the groove width.