An illumination control device controls the level of artificial lighting depending upon the intensity of natural light in the area being controlled. A single adjustment is used to set the switching point at which the illumination control device becomes operative. An indicator is provided to indicate the adjustment status before a change in the artificial light condition occurs. A filter is employed to produce turn-on and turn-off time delays which differ from one another and are automatically changed in accordance with the instantaneous light level which exists prior to a necessary circuit switching operation.