What is an LED?

We tend to use many LED lights in ThingLearn projects because they are a fast and easy way to see how circuits work. They are usually small lights with plastic casings in varying colors with two leads, or 'legs', one shorter and one longer. One of the leads is an anode (+), the other is a cathode (-).

• When the appropriate voltage is applied to the device, electrons enter it via electrons and holes, recombine, and thereby release their energy as photons, which are particles of light.
• Holes are the lack of an electron where it could exist in an atom.
• An LED is a semiconductor p-n junction diode, meaning it is created of a conductive material that is 'doped', or contaminated, with impurities to create a p-n junction.
• Current flows from the p (anode) to the n (cathode) junction.
• When electrons travel into the diode via electrical current, they are able to recombine with holes and thereby release energy, forming electroluminescence.
• LEDs can be in various colors depending on the materials used to create the semiconductor in the device.

More information can be found here