Patent ID: 7309153

Claim:
A surface light source device comprising: a light guide plate, a primary light source performing light supply to said light guide plate sideways and light control member, said light guide plate having an emission face provided by a major face and an incidence face provided by a side end face extending in a right-and-left direction as viewed from the primary light source; said light control member being disposed along the emission face and deflecting a proceeding direction of light emitted from the emission face as to let the proceeding direction come near to a normal direction of the emission face, wherein said light guide plate is provided with an emission-directivity-giving-means giving a directivity to an inner propagation light within the light guide plate so that directivity of emission from the emission face is modified, and, under definition that the normal direction of the emission face is +Z-direction and a direction of said light supply is +Y-direction and an extending direction of said side end face is ±X-direction, said light control member is provided a plurality of prismatic projection rows running in an oblique direction inclined clockwise or anticlockwise with respect to ±X-direction as viewed from +Z-direction side while said incidence face is provided with a plurality of incidence control portions each of which has first and second parts providing first and second side faces extending in ±Z-direction, the first side face being left-hand-located and the second side face being right-hand-located as vied from −Y-direction side, and each of the incidence control portions is further configurated asymmetrically with respect to a plane which is perpendicular to ±X-direction and passes a boundary line between said first and second side faces, thereby causing an inner propagation light generated when light emitted from said primary light source enters into said light guide plate through each of said incidence control portions to have a sector-like spread, in a plane parallel to said emission face, which has a center axis inclined, with respect to +Y-direction, either anticlockwise under a condition that said oblique direction is inclined clockwise or clockwise under another condition that said oblique direction is inclined anticlockwise.