A selenium cell is a light-sensitive device used in many types of photographic exposure meters. It generates an electrical current proportional to the amount of light falling on its surface, allowing photographers to measure light levels accurately and determine proper exposure settings.
Selenium cells were widely used in traditional cameras and handheld meters before the advent of modern silicon-based sensors. Their ability to provide reliable, battery-free light measurement made them an essential tool for photographers seeking consistent and precise exposure in various lighting conditions.