Electro-optical properties of reflective positive-contrast LCDs: how to obtain meaningful measuring results

The authors have measured angular contrast LCDs (liquid crystal displays) under point source and diffuse illumination and compared the results to those of the transmissive mode. The comparison shows that under point source illumination parasitic effects determine the resulting contrast distribution rather than intrinsic properties of the LC-layer and that the basic features of the transmissive mode (e.g. main viewing direction) cannot be reproduced adequately. In order to obtain reasonable and meaningful results, specular and diffuse components of the light reflected by LCDs must be separated during the measurement of the angular contrast distribution. This can be conveniently achieved with the diffusing hemisphere, a device that also allows for the measurement of the diffuse/normal reflectance factor, a suitable figure of brightness for reflective LCDs.<>