Abstract: An anti-dazzle rear view mirror incorporates a liquid crystal cell the conductive layers of which are energized by a control voltage in response to light above a threshold intensity impinging on a photoresistor in the control circuit of the cell. A low voltage source, for example a vehicle 12 volt battery, supplies a potential divider which includes the photoresistor, the voltage across which is connected through a logic invertor which controls two logic NAND gates for gating antiphase square wave outputs derived from an oscillator driven from the source to the respective conductive layers of the cell, thereby producing a square-wave voltage across the cell which is double the amplitude of the oscillator output, and decreasing the time taken for the liquid crystal cell to respond to the light intensity change.