Patent ID: 6906452

Claim:
An electroluminescent display comprising: a light transparent substrate; and an electroluminescent layer provided on said light transparent substrate, said electroluminescent layer comprising at least a transparent electrode, an organic luminescent layer, and a cathode, wherein (1) two or more regions with different refractive indexes are provided within said light transparent substrate and (2), as viewed in cross section of the substrate, a boundary line between the higher refractive index region and the lower refractive index region is a tapered line satisfying a requirement represented by the formula θ 2 ≧θ 1 −sin −1 (n 2 /n 1 ) wherein θ 2 ≧ 0 , θ 1 represents the angle of light radiated from the electroluminescent layer to a direction normal to the substrate; θ 2 represents a taper angle at a point where, when θ 1 has been increased, the light is applied to the interface between the lower refractive index region and the higher refractive index region; n 2 represents the refractive index of the lower refractive index region; and n 1 represents the refractive index of the higher refractive index region.