Patent ID: 8704441

Claim:
A surface light source device comprising: an organic electroluminescent element having a light-emitting surface for emitting light; and a light output surface structure layer provided on the organic electroluminescent element on a side of the light-emitting surface, wherein the light output surface structure layer includes concave portions which are relatively recessed and convex portions which are relatively projected, the concave portions and convex portions being provided on a surface opposite to the organic electroluminescent element in an alternate manner along an in-plane direction parallel to the surface, the depth of each concave portion is 1 to 50 μm, and the bottom of the concave portion and the top of the convex portion that are adjacent to each other are distant with distances in a thickness direction of the surface light source device, the distances being made uneven with a standard deviation range of not less than 0.05 μm.