Patent ID: 7719642

Claim:
A back light device for a liquid crystal display device, comprising: a light source providing light; a light waveguide plate guiding light from the light source, and said light waveguide plate having an emitting surface, a front surface and a bottom surface, the emitting surface being adjacent to the light source; a reflector arranged under the bottom surface of the light waveguide plate, reflecting light; and at least one single layer cholesteric liquid crystal (CLC) film arranged on the front surface of the light waveguide plate, collimating light, wherein the at least one single layer CLC film transmits a first circularly polarized vertically incident visible light and circularly polarized obliquely incident light having a wavelength greater than about 780 nm and wherein the at least one single layer CLC film reflects a first circularly polarized obliquely incident visible light, a second circularly polarized vertically incident visible light and a second circularly polarized obliquely incident visible light having a wavelength range from 380 nm to 780 nm and a circularly polarized vertically incident light having a wavelength greater than about 780 nm.