Illumination system using cholesteric polarizer, linear polarizer for such illumination system and display device comprising such as illumination system

摘要

The Application relates to an illumination system comprising a fluorescent lamp and a broadband, cholesteric polarizer. Such a polarizer contains a layer of a polymeric material having a cholesteric order, which material is ordered in such a way that the axis of the molecular helix extends at right angles to the layer. The broadband character of the polarizer is obtained by causing the pitch of the molecular helix to increase from a minimum value at a first surface of the cholesteric layer to a maximum value at the second surface of the layer. In accordance with the invention, the polarizer should be positioned in the illumination system in such a manner that the cholesteric layer is directed towards the fluorescent lamp with its first surface. In addition, the value of the product pmax.ne of the maximum value of the pitch in the cholesteric layer pmax and of the extraordinary refractive index ne must range between 0.61 micron and 0.76 micron. By virtue of these measures, the illumination system has a surprisingly low viewing-angle dependence of the lightness and the color. The Application further relates to a linear polarizer for use in this illumination system as well as to a display device which comprises such a linear polarizer.