Optoisolators are normally a combination of two distinct devices: an optical transmitter, typically an IRLED, and an optical receiver such as a phototransistor or Photologic® device. The optoelectronic components are separated by an isolating transparent barrier which blocks any electrical current flow between them, while allowing the passage of light. This allows for very large isolation voltages-typically several kV’s. On the transmitting side, the circuit is connected to an LED that lights up whenever an electric signal is applied to it through the circuit. This light is then transmitted to the other circuit using a light-transmitting medium (Light Channel). On the other side there is typically a phototransistor or Photologic® sensor that detects the light wave and then generates an electric signal. This permits the electric signal to be transmitted without direct electric wire connection.