Patent ID: RE41566

Claim:
A liquid crystal display device including a liquid crystal display panel and a back light device, said back light device comprising: a light source for emitting light; a light guide means having a top surface facing a back surface of said liquid crystal display panel and a side surface receiving said light from said light source; a reflector means provided on a back surface of said light guide means; and an optical film of transparent material positioned between said back surface of said liquid crystal display panel and said top surface of said light guide means, including a first surface having a wave structure including a plurality of regularly spaced isosceles triangles prisms arranged side-by-side, the prisms having smooth surfaces, and a second surface having an optically rough structure for performing diffuse transmissions, wherein a top angle of said isosceles triangle prisms is in a range of 95 degrees to 120 degrees for flat, angles prism surfaces to gather light from the diffuse transmission into a desired viewing angle for the liquid crystal display panel , wherein a polarizer is positioned between said liquid crystal display panel and said optical film, and a direction along which said peaks and valleys of said isosceles triangle prisms are oriented is aligned in parallel to a polarizing axis of said polarizer and the tops of the isosceles triangle prisms are not farther than 160 μm apart .