LED

An LED is a light-emitting diode. LEDs are, as the name implies, a type of diode. Diodes are a special kind of device that only conduct electricity in one direction, and an LED is a variation that emits light while it is conducting electricity. Once a diode starts conducting, it begins to act like a short-circuit in the wire. Short-circuits cause things to heat up really fast and explode, so that’s not what we want at all. We have to pair a diode with a resistor in order to limit the current. This is called a current-limiting resistor, and the behavior of the resistor simply follows the equation V = I*R. If we only want 10mA to flow along a path, we might put a 500 ohm resistor in, because our pins output 5V, so therefore 5 = 10mA * R which means that 5 / (10mA) = R, R = 5 / 0.01, R = 500 ohms.