Apparatus and method of controlling driving voltage for image display device

An apparatus for controlling a driving voltage for an image display device having a polarization angle adjustor for adjusting the deflection angle of a digital liquid crystal display device, the controlling apparatus comprising:

• an optical sensor for sensing light projected to a screen and converting the light into an electrical signal;
• a driving control circuit for adding a first square wave driving signal with a predetermined frequency and amplitude to a second square wave driving signal with a higher frequency and lower amplitude than those of the first square wave driving signal, thereby to generate an added signal, applying the added signal as a driving signal of the polarization angle adjustor, and controlling the voltage of the first square wave driving signal so that the difference of a change in luminance is minimum, using the difference of the electrical signal of the optical sensor obtained due to a change in the level of the second square wave driving signal during one cycle.