An electric eye can act as a switch to turn another device on or off. For example, an electric eye placed opposite a light across a conveyor belt can count objects on the belt. Each time an object comes between the light and the electric eye, the current flowing from the eye stops. A counting device connected to the eye then adds one number to the total. Electric eyes can turn on street lights or house lights when darkness falls, set off burglar alarms, and perform similar jobs.
Electric eyes can also measure amounts of light.
The electric eyes on some cameras measure the light and then properly adjust the lens. Motion-picture projectors use electric eyes to produce sound from special patterns on the film. Some TV equipment uses electric eyes to produce TV pictures. How electric eyes work. Scientists call electric eyes photoelectric cells.