Abstract: A photocathode current sensing circuit (58) is provided to adjust the electron accelerating voltage to a cone (32) and a phosphor screen (34) on an image intensifier tube (26). The voltage is adjusted by an anode power supply (60) which is responsive to the photocathode current sensing circuit (58). As light strikes the photocathode (28), a current (56) is generated. The current (56) is directly proportional to the intensity of light striking the photocathode (28). As the light and the current (56) decrease, the sensing circuit (58) controls the power supply (60) to provide a higher voltage to the cone (32) and the screen (34). By increasing the voltage to the cone (32) and the screen (34) the electrons are provided with more acceleration and, therefore, are intensified for viewing on the screen (34). An increase in light operates oppositely and decreases the intensity on the screen (34).