How to find positive (anode) and negative (cathode) terminals of an LED

By | April 27, 2015

In this post you are going to learn about identifying LED positive and negitive terminals.

LED stands for Light Emitting Diode. It’s a p-n junction diode and able to emit light when connected in forward bias. LEDs are pretty commonly used in the embedded devices to get indications, feedback, notifications. They are available in different colors, shapes, sizes and light weighted, consumes very less power.

Identifying LED positive and negative terminals:

As mentioned earlier LED is nothing but a p-n junction diode. So, it should have a cathode and anode. For interfacing an LED, first thing you need to do is to identify the positive and negative terminals. This is pretty simple, there are several ways to do that. Let discuss one by one.

Identifying Positive (anode) and Negative (cathode) sides of a new LED :

As you can see in the below picture, a new LED legs are not even, you shall see difference. This makes our work easier.

Longer leg is always positive terminal and shorter leg is obviously a negative terminal. 

Identifying LED positive and negative-1

Finding the positive and negative terminal of a used LED :

What if someone cut the LED legs? There are several ways to identify the positive and negative sides in this situation.

Find the flat spot:

If you observe the plastic body of LED, you will find a flat spot. The flat spot side is negative terminal and other side is positive terminal. 

Observe the LED core:

Inside LED plastic body, you will find bigger and smaller leads. Bigger lead is cathode or negative terminal and smaller lead is anode or positive terminal. 

Identifying LED positive and negative

Using Multimeter to identify positive and negative sides :

Accomplishing this task is very easy if have a multimeter. Refer below procedure.

  1. Change the multimeter into diode testing mode. (or) Rotate and set multimeter dial at diode symbol.
  2. Then connect Multimeter probes to LED legs.
  3. If you see a LED blink, then positive side of probe is LED positive terminal and negative side of probe is negative terminal.

Identifying LED positive and negative-using multimeter

Hope this helps.

3 thoughts on “How to find positive (anode) and negative (cathode) terminals of an LED

  1. Fred Jenkins

    Trying to do this on electric radiator fan on car need to make the fan push the air from front of radiator any suggestions

  2. Aiswarya

    Is it true that the longer lead of an LED is negative .
    And i have a question for you
    Where should a negative lead be connected in a battery – to the positive or negative terminal

  3. Aiswarya

    The question of the lead is asked becoz in each website there are different answers


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