Collimator utilizing wavelength selective reflection and backlight system

摘要

A flat plate collimator and backlight system capable of improving the display characteristics of liquid crystal display devices are obtained. In order to achieve this end, a collimator is provided which comprises a cholesteric liquid crystal layer exhibiting a selective-reflection wavelength band with respect to perpendicularly-incident light in the wavelength range lambda1 to lambda2 (lambda1<LAMBDA2), and which satisfies the relation lambda0<LAMBDA1 with respect to the maximum-emission wavelength lambda0 in the emission spectrum of the light source with which the collimator is used in combination, and a backlight system employing this collimator and light source is provided.