Patent ID: 7736045

Claim:
A plate-shaped light guide for a planar light source device that guides a light emitted from a primary light source in a point state, comprising: a light incident end face on which the light emitted from the primary light source is incident; a light emitting face being disposed perpendicular to the light incident end face and through which the guided light is emitted, and a back surface on the opposite to the light emitting face, wherein a plurality of first elongated lenses having an average slant angle of 0.5 to 60° are continuously or intermittently formed on one of the light emitting face and the back surface, and the plurality of first elongated lenses are each an elongated prism having two prism surfaces, and at least a portion of the prism surfaces includes a rough surface having an average slant angle of 0.1 to 8°, and at least a portion of the other one of the light emitting face and the back surface includes a rough surface having a slant angle.