Patent ID: 8894263

Claim:
An optical plate, comprising: a supporting sheet having a top surface and a bottom surface; a first optical layer disposed on a bottom surface of the supporting sheet, the first optical layer having a first refractive index and a top and a bottom surface, the bottom surface having a plurality of first protruding portions, wherein each of the first protruding portions has a first cross section perpendicular to the bottom surface of the first optical layer, the first cross section being a first portion of a triangular prism; a second optical layer contacting the bottom surface of the first optical layer, covering the first protruding portions and filling indented regions formed between adjacent first protruding portions wherein no space remains between the first and second optical layers, the second optical layer having a second refractive index, wherein the second refractive index is higher than the first refractive index; a third optical layer having a top and a bottom surface, the bottom surface contacting and covering the top surface of the supporting sheet, the third optical layer having a plurality of second protruding portions on its top surface and having a third refractive index, wherein the third refractive index is lower than the second refractive index and the third refractive index is the same as the first refractive index, wherein each of the second protruding portions has a second cross section perpendicular to the bottom surface of the third optical layer, the second cross section being a portion of a triangular prism; and wherein the first protruding portion of the triangular prism has a first vertex angle, the first vertex angle being in a range from about 75 degrees to about 80 degrees.