Optocouplers transmit a signal while electrically isolating the transmitting and receiving sides. They play a key role in protecting sensitive electronics and the consumer from high voltage spikes. A current turns on the infrared emitting diode, the infrared light from the IRED travels through the transparent dielectric material to a photo detector. The photo detector generates current which is then used to perform various functions. The dielectric allows light to pass but blocks electrical noise and voltage spikes.