Light-induced transmission changes in liquid crystal displays for adaptive pattern projection

The changes in the transmission and contrast properties of a super-twisted nematic liquid crystal display panel, induced by the light impinging on the panel itself, have been studied. Upon illumination by laser radiation with power density close to that used in practice, the transmittance of the panel increases or decreases according to the brightness voltage that sets the transmittance level. The dynamics of the transmittance change are typically bi-exponential, with a shorter decay time on the order of a fraction of a second and a longer decay on the order of tens of seconds. The observed changes were interpreted and modeled by considering local temperature changes in the crystal because of the light impinging on it. The temperature changes produce a shift of the transmittance curve and a change of slope in its central region. The presence of the dip after the Frederickzs region accounts for the anomalous behavior of the transmittance in that portion of brightness voltages