Witness a late night in Mexico: the vibrant decor at Los Helechos, eating chicken in zucchini flower sauce, a Negro Modelo close at hand, a brief pause in the table conversation occurs. My father, engineer and thinker of strange thoughts, asks to the table at large, "How does an LED work?". I mumble something unconvincing about electrons flying into orbit around molecules and losing energy in the form of light. A hush settles over the table and then talk turns back to our time on the beach that day. That question has plagued me for weeks.
In my diligent quest for understanding LEDs I have stumbled upon a gem of a site called The Naked Scientists. The Naked Scientists are a BBC science radio program, podcast, and web site all in one. They allow you to explore science, medicine and technology news, discoveries and breakthroughs being discussed by scientists and researchers today and include interviews with famous scientists of world-class reputation. What a treasure trove!
So how does an LED work? A Light Emitting Diode involves two types of semi-conductors sandwiched together: an N-type and a P-type. The N-type is heavy in extra electrons and the P-type is full of molecules that need electrons (think of these as electron attracting holes). By applying a current to either side, the electrons from the N jump over to the P and fall into the holes. When they do so they give up their extra energy as light. Check out the great description of this phenomenon at the Naked Scientist website.