Image Number 19 for United States Patent #7180664.
A light diffusion sheet or film including a plurality of unit lenses formed of a material having a refractive index N1, each unit lens having a trapezoidal cross-section. At least one between lens portion, having a triangular cross-section, positioned between two of the unit lenses. The between lens portion is formed of a material having a refractive index N2 that is less than N1. If .theta. represents an angle defined by a side of the trapezoidal cross-section and a line normal to a base of the trapezoidal cross-section, then sin(90-.theta.)>N2/N1 and N1<1/sin(2.theta.).