Patent ID: 8018555

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; and at least one cholesteric liquid crystal (CLC) film arranged on the emitting surface of the light waveguide plate, collimating light, wherein the at least one 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 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.