CHOLESTERIC LIQUID-CRYSTAL DISPLAYS ILLUMINATED BY DIFFUSE AND PARTIALLY DIFFUSE LIGHT

We report on the photometric and colorimetric properties of surface an d polymer network stabilized reflective cholesteric displays. Both dif fuse and partially diffuse illumination are used, the latter being an experimental approach to emulating typical room light conditions. It i s shown that addition of polymer increases the field of view while dec reasing angular dependence of the color quantities: hue, chroma, and l ightness. Total luminance and contrast ratio, however, are also decrea sed. 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 whe n viewed in a geometry void of specular reflection. Colorimetric quant ities in surface stabilized cells are less sensitive to illumination g eometry. This suggests that for displays in which specular reflection has been suppressed, surface treatment represents the best method of s tabilization. If the viewing angle allows specular reflection, polymer stabilization yields the largest luminance and contrast ratio. This b ehavior is explained in terms of angular distribution of helical axes due to presence of the stabilizer. (C) 1996 American Institute of Phys ics.