How Are Street Lights Turned on?
Street lights turn on automatically by means of a photoelectric cell which turn them on at dusk, off at dawn, or activate automatically in dark weather. Photocells detect if light is needed.
(Photocells are light-sensitive sensors that respond to the amount of light detected. When the light is too low, the sensor tells the computing unit within the street light to activate the flow of electricity. When the photocell detects too much light, the sensor will deactivate the street light.)
During the daytime, sunlight shines on a small photocell on the top of the street light. This generates an electric current that activates an electric switch which turns the light off. At night, when sunlight no longer shines on the cell, the photocell current stops. The light switch shuts off automatically and turns on the light.
Parking lot street lights are controlled by a clock-like timing device which is set to turn the lights on and off at certain hours during the nighttime.