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.
Phototubes are special vacuum or gas-filled tubes that contain photosensitive materials. These materials give off electrons when light strikes them. Every phototube has a cathode made of photosensitive material, and an anode. When light strikes the cathode, it causes electrons to flow to the anode and creates a current. See Photomultiplier tube .