A photo transistor is a light-sensitive electronic component that functions like a switch, allowing current to flow in response to light. In photography, it is commonly used in the slave triggering of electronic flash units, enabling one flash to activate others automatically when it fires.
Photo transistors are valued for their sensitivity and speed, making them essential in multi-flash setups and automated lighting systems. By detecting light and responding quickly, they help photographers achieve precise exposure and creative lighting effects without manual intervention.