Patent ID: 8476825

Claim:
An organic electroluminescent light source device comprising a first transparent electrode layer, a light-emitting layer, a second transparent electrode layer, and a reflective layer having a reflective surface, in this order from a light-emitting surface side, and further comprising a structural layer X that is provided between the second transparent electrode layer and the reflective surface and is in contact with the reflective surface, wherein the reflective surface has a concavo-convex structure, the concavo-convex structure has a plurality of concavo-convex structure units formed of depressions or protrusions, and a refractive index n of the structural layer X, an inclination angle θ×1 (°) of the concavo-convex structure units, and a mean inclination angle θ×2 (°) of the concavo-convex structure at the reflective surface satisfy the following expressions (1) and (2): θ×1≦sin −1 (1/ n ) (1) {90−sin −1 (1/ n )}/3≦θ×2≦sin −1 (1/ n ) (2).