Method and device for the polarizing of an LCD screen as a function of the ambient luminosity

The present invention relates to the electrical polarization of a liquid crystal display screen or LCD screen in order to obtain an image whose readability depends as little as possible on the ambient luminosity. To obtain improved readability of a liquid crystal display screen under varied conditions of ambient luminosity, it is possible to increase the dynamic range of variation of the polarizing voltage. However, this leads to an increase in the electrical power consumption and to contrast reversal defects. To prevent this phenomenon, it is proposed not to modify the dynamic range of variation of polarizing voltage but to shift this range towards the lower voltages when the ambient luminosity increases or towards the higher voltages when the ambient luminosity diminishes. Thus, the white level is favored under high ambient luminosity and the black level is favored under low or normal luminosity.