First lets define an LED.  LED stands for Light Emitting Diode. There’s been a lot of talk lately in the news about the benefits of LED’s including the low power requirements (a fraction of what current light bulbs use), the fact that most of the energy is not lost in heat (like incandescent bulbs), and the long life span of the LED at approximately 10 years.  With all these great benefits it should be taken as a given that they will eventually be the primary means of lighting our homes.

Back to how it works… A diode is a semiconductor, a material with a differing conductivity.  For an LED the conductor material is Aluminum-Gallium-Arsenide bonded into a single molecule (AlGaAs).  Normally in this molecule all the valence electrons are  collectively shared (meaning no electrons are left free).  In semiconductors extra free electrons are added, or holes for electrons to pass through the molecules are created, by adding various atoms of different elements (impurities to the above AlGaAs).  This process is called doping.

When the doping results in extra electrons, its called an N-type material.  When holes are created for the free passage of electrons it is called a P-type material.  In both types the result is that electrons can moved from negatively charged areas to a positively charged area.

In a diode you have a section that is made of a N-type material bonded to a section of P-type material.  Both of these sections are connected with electrodes which then connect to the positive and negative terminals of an energy source (like a battery).  In the absence of a charge extra electrons from the N-type material fill the holes left in the P-type material.  In fancy terms this causes a depletion zone in between the two materials causing a polarity of the diode, with all the electrons on one side (N-type material) and all the holes lacking the electrons on the other (P-type material).

Apply a current large enough and you’ll break the bonds in the depletion zone and start the free flow of electrons again.

As the electrons flow they release energy in the form of photons.  Since they are moving in opposite directions the process is a never ending reaction.

To see a great example of a led click here.