A photodiode is a light sensitive diode that converts an optical signal into an electrical signal. A photodiode is very similar to a light emitting diode (LED), except that a photodiode detects light while an LED emits light. Photodiodes are often used in compact disc players, smoke detectors, and television remote control systems. They are also used to measure light intensity. In this activity, you will write your own LabVIEW program to control the on/off state of an LED with a photodiode. The photodiode will act as a light-activated switch.