What components contain a transistor and a light source?

A common component that contains both a transistor and a light source is an opto-isolator or opto-coupler. This device uses a light-emitting diode (LED) as the light source and a phototransistor to detect the light, allowing for electrical isolation between its input and output. Another example is a LED driver circuit, which includes transistors to control the current flowing to the LED, ensuring optimal brightness and efficiency.