photoelectric device used to generate or control an electric current. Selenium photocells are commonly used in photographic-exposure meters, burglar alarms, electronic-door opening and counting devices, electronic control systems in factory assembly lines, and industrial colour perceptors. In some ways, such as colour perception and sensitivity, the performance of selenium photocells is superior to that of vacuum-tube photocells, but response is slower, making selenium cells unsuitable for high-fidelity sound reproduction from an optical sound track on motion-picture film.