Variable photoelectric cell

摘要

An illumination control device for regulating the illumination in a controlled lighting area responds to natural illumination to control artificial lighting. The illumination control device turns the artificial light on and off at independently variable natural illumination levels to provide a hysteresis between the turn-on and turn-off points of the artificial lights. In addition, a variable time delay is included in the illumination control device to delay the turn-off of the lights for a variable period of time after the natural light level has risen above the level required for artificial light turn-off. Furthermore, the illumination control device includes a circuit for turning on all of the lights, regardless of the natural illumination level, when the circuit is initially energized so that the lights can be checked by maintenance personnel.