Photocells, also known as light sensors or photoresistors, are electronic devices that detect light levels in their environment. They work by changing their electrical resistance based on the amount of light they receive. When light levels are high, the resistance decreases, allowing more current to flow, while low light levels increase resistance, reducing current flow. These devices are commonly used in various applications, such as outdoor lighting systems, where they automatically turn lights on at dusk and off at dawn. Photocells can also be found in solar panels, security systems, and smart home devices, enhancing energy efficiency and convenience.