Updated on : 31 dec 2008

How you can determine anode and cathode of LED. I know its tooooo trivial but still …


Most common method

When you purchase an LED … longer leg is anode while shorter leg is cathode. What if you have cut the two leads to same length ?? read on …

Method 2


p align=”justify”>- Take one resistor between any value between 100Ohm to 500Ohm and connect it in series with the LED on bread board.
– Give a supply (from 3 to 9V). If LED glows, lead connected to VCC is anode and other one is cathode.

What if you don’t have breadboard or you are too lazy (like me :) ) to do this testing …

Method 3DMM_diodeTestMode_thumb2

  • Take multimeter and keep it on Diode testing mode.
  • Connect one lead of LED to COM probe of DMM and another to RED probe.
  • If you get some reading on DMM, then lead connected to COM is cathode and other one is anode. If not reverse the LED and recheck.

What if you feel (like me :) ) this method is also too boring and time consuming …

Method 4


p align=”justify”>- Take LED in your hand and look carefully at the place where leads go into LED.
– Look at the border ring which is slightly projected out.
– You will find, on one side, this ring is flat. That’s the cathode !!!! and other one is anode.

…and this will be True for almost all LEDs that you purchase from general retail electronic shops.
Note: Some companies do not follow this convention for certain special purpose LEDs.


  1. could you please help me how do you identify if both legs the anode and the cathode have been cut the same lenght

    • Omkar

      read the post again :)

  2. Aditi

    very much thanks for info.

  3. Darnko

    I haven’t been working around diodes for a spell, and with me getting worse the older I get, I can forget such a simple way of telling a cathode from an anode. I can’t believe how far down it is on a Google site and even here it method #4. Well that was it, at least they had it. I just knew there was something besides using resistors and so on.


  4. best method for highlighting the quality of education tips thanks

  5. Abhisek kora

    thanks for this information…….

  6. purna chander

    thkq. i got information which i was looking for.

  7. Sanjeev Garg

    in method 3, DMMconnection, we can also recogonise if the LED glows after connecting with DMM as it is in series with 3V DMM supply.
    Also you have explained good methods. Thanks

  8. nima

    Hello.thanks for this … I am a iranian … I like LEDs


  9. Hello, i found your site at yahoo and you are providing interesting stuff. I like it,

  10. Bruce

    Thanks for the info, one question though.
    What happens if i get the anode and cathode the wrong way around in a circuit? Nothing? Or something (BANG!)???
    Trivial question for ‘Trivial’ info.
    Thanks again.

    • Omkar

      nothing will happen. since led (Light Emitting Diode) is basically a diode which needs to be forward biased to operate. If you connect in wrong way, diode will be reverse biased and it will as as open circuit.

      • arun

        led is a forward biased p-n junction diode.If anode and cathode are interchanged,diode becomes reverse biased.Therefore it is characterized by a peak inverse voltage.It is the maximum reverse voltage applied across the diode without burning the diode.


  11. Regarding Method 2…..

    “Give a supply?”

    What is the recommended DC Voltage?

    • Omkar

      anything from 3 to 9 V.


  12. thx.


  13. Roger

    Perfect. Exactly the information I was looking for… trivial or not!


  14. nice.
    It could be cool to add stuff for RGB led with common cathode or common anode.
    A little mistake in the shipment I received just gave me headache…
    sold to be common cathode, they were common anode.
    now, I understood..

    nice website!!

    all the best,


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