Optimum polarizer combinations for twisted nematic displays

We present a simple phenomenological theory that makes it possible to compute the brightness and contrast ratio of reflective twisted nematic displays from the optical characteristics of their polarizers. The theory satisfactorily explains the large change in contrast ratio that is observed when the positions of the polarizers are interchanged in a reflective display assembled with dissimilar polarizer types. Brightness and contrast measurements are reported for reflective displays assembled with the four possible combinations of Polaroid HN-42 and HN-55 sheet-type polarizers, and the results are in good agreement with theory. Optical characteristics of polarizers are suggested which should markedly improve display viewability over what is currently obtainable. We find that a small increase in contrast ratio is possible if the front polarizer of a display is made stronger than the rear polarizer instead of employing identical polarizers.