Phototransistors
Phototransistors are semiconductor devices that convert light into electrical signals. They are similar to regular transistors in the sense that they both employ an amplifier and two electrodes, with the dividing line between them allowing current to flow through. However, unlike regular transistors, phototransistors use a light source rather than an electric power source to control the flow of current. When light shines on the phototransistor, it creates a voltage differential between the base and collector electrodes that can be used to control the current that flows through the device. Phototransistors are often used in light-sensing applications, such as automatic door openers, fire alarms, and robotics.