The Photodiode sensor is a system accessory for Greengate lighting control systems. It allows control of lighting levels based on how much natural light is present. The Photodiode Sensor combined with an electronic dimming ballast regulates illumination in a monitored area to maintain a constant light level regardless of the amount of natural light present. Sensor can be used in indoor applications. The Photodiode Sensor measures the actual amount of illumination within a work area or monitored zone. It compares the light level to a preset footcandle (FC) calibration and send a voltage signal to a dimming ballast to either increase or decrease the lighting in flourescent lamps. This ensures that there is a constant level of illumination within the controlled area. A potentiometer adjustment on the Photodiode Sensor is calibrated to preset the light level.