Introduction: Identifying LED Pins

I have three simple ways to remember which way round an LED goes in a circuit. 

1,  Looking down from the top of the LED there is usually a flattened edge, this identifies the negative pin of the LED. 

2,  If the LED is new, there will be one lead longer than the other. The long lead is the positive pin and the short lead will be the negative pin.

3,  If you hold the LED sideways on and view through the plastic, there will be two parts, a small straight pin and a fatter 'L' shaped pin.  The small pin is the positive side and the fatter 'L' shaped pin is the negative side.

My picture illustrates the three possible ways to identify an LED and also shows the polarity as would be drawn in a circuit diagram.

Comments

author
neontime (author)2014-05-22

Beware though... for Infrared LEDs the "L shaped pin" is often the anode. In all cases however the flat edge and the shorter lead are the cathode.

author
BenHarper (author)neontime2016-05-10

Not in all cases - as I have recently spend a little while troublshooting!

https://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTL-4266N.pdf

author
BenHarper (author)neontime2016-05-10

Not in all cases - as I have recently spend a little while troublshooting!

https://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTL-4266N.pdf

author
holymoses (author)2015-07-18

Well...practically....it is not so easy to find out for everyone without a magnifyer and then it is quite easier just to have a 5 buck Multimeter supporting an eloquent function to find out if this little item still works or is broken.

The eloquent instructable to this basic knowledge would be: "How to open a technical book and find what you are looking for"!

The same with resistors, all that theoretical color-ring discriminating...it all sucks!

author
holymoses (author)holymoses2015-07-18

PS: ...if the pins are already cut in any way!

author
Slowpoke (author)2012-07-09

Good techniques to remember. I use a similar system which is;
Look into the LED from the side, the fatter 'L' shaped pin seems to form a çup that the LED chip sits in. Cup=Cathode. The smaller pin with the wire going off to the LED chip can be called the arm. Arm=Anode.
Cup = Cathode.
Arm = Anode.

Easy to do if the LED body is clear but if it is coloured, just hold it up to a light source and the internal structure can be seen.

author
pussiedoctor (author)Slowpoke2012-07-12

Nice and simple, great tip, thankyou for sharing.

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