ALLNET Brick'R'knowledge LED red
The red LED (Light Emitting Diode) is protected against overload with a series resistor. It only lights up when the diode is connected in the direction of flow, i.e. the current flows from the anode to the cathode. LEDs require a minimum voltage in the direction of flow in order to light up. For red LEDs it is approx. 1.5V.