Patent ID: 8373647

Claim:
A surface light source device comprising: light sources; and a plurality of light guide members, each light guide member having a light incidence surface for light entering from each of the light sources, and making surface light emission based on incident light from the light incidence surface, wherein the plurality of light guide members are arranged on the same plane, and wherein each light guide member has tapered surfaces adjacent to the respective light incidence surface, and each tapered surface having a predetermined angle against the respective light incidence surface in which the following conditional expression is satisfied: θ t≦ 180−(θmax+θ c ) where θt is an angle of the light incidence surface against each tapered surface, θmax is a maximum value of a radiation angle (half-value angle) of light entering from the light incidence surface, and θc is a critical angle when light enters from the light guide member to a gap between adjacent light guide members.