Patent ID: 7226197

Claim:
A light guide for a surface light source device having a plate-like shape that guides light emitted from a point primary light source, comprising: a light incident end surface to receive light from the primary light source; an elongated lens forming surface to spread light received from the light incident end surface, the elongated lens forming surface includes a plurality of elongated concave/convex structures arranged substantially in parallel to each other and extend substantially along a direction of directivity of light, wherein a plurality of micro regions defined over a specific number of the plurality of elongated concave/convex structures in cross section thereof, wherein a distribution of the micro regions having an inclination angle between 20° and 50° is more than 10% over all micro regions in the vicinity of the primary light source, such that the inclination angle is formed by a tangent to each micro region and is defined in an absolute value; and a light outputting surface to output the guided light having a light outputting functional structure.