Method and apparatus for biasing an LCD screen depending on environmental illumination

摘要

In strong lighting a polarisation voltage (VB1) corresponding to white is chosen to be lower than the changeover voltage (Vb) and for a limited dynamic (D) this results in a polarisation voltage for black (VN1) where VN1=VB1+D. In weak lighting the white polarisation voltage VB2=VN2-D where VN2 is a value favouring black uniformity rather than white transmission. A photodetector measures the ambient lighting level and an analogue to digital convertor supplies a comparator with access to a memory storing polarisation reference voltages and reference voltage levels for gray. The voltage/light transmission characteristic is moved towards the lower voltages favouring white when the lighting increases and towards the higher voltages favouring black when the lighting is poorer.