Patent ID: 8220978

Claim:
A brightness enhancement film, comprising: a light transmissive substrate, having a first surface and a second surface opposite to the first surface; a plurality of lenses, disposed on the first surface, wherein each of the lenses has a curved protruding surface facing away from the light transmissive substrate, the radius of curvature of the curved protruding surface in a first direction parallel to the first surface is R 1 , the radius of curvature of the curved protruding surface in a second direction parallel to the first surface is R 2 , and R 1 ≠R 2 ; and a reflective layer disposed on the second surface, wherein the reflective layer has a plurality of light transmissive openings, the light transmissive openings are respectively located on the optical axes of the lenses, and the distance between the apex of the curved protruding surface of the lens and the corresponding light transmissive opening is L, the refractive index of the lenses is n, and the brightness enhancement film satisfies L<nR 1 /(n−1) and L<nR 2 /(n−1).