Light Emitting Diode (LED) Polarity

LEDs are diodes and diodes can only allow electrical current to flow in one direction, therefore LEDs are polarised. The positive pin is the ANODE (+) and the negative pin is the CATHODE (-).

It is very important that LEDs are connected to a circuit in the right direction. The current flow can flow only from the ANODE (+) terminal to the CATHODE (-) terminal.

If the LED is connected in the wrong direction it will not illuminate. the circuit diagram symbol for an LED is shown below and the direction of flow is also indicated by the arrow. (Learn more about Electrical Circuit Symbols).

There are a few indicators that can help you work out which pin of the LED is the cathode and which pin of the LED is the anode.

  • In most cases the long 'leg' or pin will be the ANODE (+).
  • If the legs have been shortened there may be a flat edge on the LED casing which will indicate the CATHODE (-).
  • Failing this - most Multimeter will have a 'diode setting' to test for polarity. When the positive probe (usually red) is touching the anode and the negative probe (usually black) is touching the cathode the multimeter will light up or show a reading.

led polarity infographic

We hope this helps you over come a basic first hurdle when using your LEDs! See Our Full Range of LEDS.