LEDs

LEDs make great indicator lights. They use very little electricity and they pretty much last forever.

In this lession you will use perhaps the most common of all LEDs a 5mm red LED. 5Mm refers to the diameter of the LED and as well as 5mm, other common sizes are 3mm and the large fun 10mm LEDs.

You cannot directly connect an LED to a battery or voltage source. Firstly, because the LED has a positive and a negative lead and will not light if they are the wrong way around and secondly, an LED must be used with a resistor to limit or 'choke' the amount of current flowing through the LED - otherwise the LED could burn out!
If you do not use a resistor with an LED, then it may well be destroyed almost immediately, as too much current will flow through the LED, heating it and destroying the 'junction' where the light is produced.

There are two ways to tell which is the positive lead of the LED and which the negative. 
  • Firstly, the positive lead is longer.
  • Secondly, where the negative lead enters the body of the LED, there is a flat edge to the case of the LED.
If you happen to have an LED that has a flat side next to the longer lead, you should assume that the longer lead is positive.
This guide was first published on Nov 29, 2012. It was last updated on Nov 12, 2018. This page (LEDs) was last updated on May 04, 2015.