Journal of Applied Physics Vol. 80

Cholesteric Liquid-Crystal Displays Illuminated by Diffuse and Partially Diffuse Light

Abstract:

We report on the photometric and colorimetric properties of surface and polymer network stabilized reflective cholesteric displays. Both diffuse and partially diffuse illumination are used, the latter being an experimental approach to emulating typical room light conditions. It is shown that addition of polymer increases the field of view while decreasing angular dependence of the color quantities: hue, chroma, and lightness. Total luminance and contrast ratio, however, are also decreased. Therefore, it is concluded that optimum polymer concentration is dependent on the viewing geometry. Luminance and contrast ratio of the surface stabilized cells exceeded that of polymer stabilized cell when viewed in a geometry void of specular reflection. Colorimetric quantities in surface stabilized cells are less sensitive to illumination geometry. This suggests that for displays in which specular reflection has been suppressed, surface treatment represents the best method of stabilization. If the viewing angle allows specular reflection, polymer stabilization yields the largest luminance and contrast ratio. This behavior is explained in terms of angular distribution of helical axes due to presence of the stabilizer.