Added on Feb 23, 2011

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Take a tour through the world of the light-emitting diode. Learn - who invented it, how to use it, and how to make your own. Collin Cunningham: People are fascinated by light. I mean just glancing over at a display of flashing lights can grab my attention. Do you ever remember sitting around a campfire? Staring at the flames and just being totally transfixed, almost like if you're watching TV. It's comforting, and it can even by hypnotic. Recently, technology has made creating light a whole lot easier to do. For that, we have this little guy to thank. The light emitting diode, or LED for short. LEDs have a lot of different uses, from a simple power on indicator to traffic signals. LEDs use about ten percent of the energy of a traditional light bulb, and they can last about thirty times longer. That makes them a pretty big hit with businesses looking to do large scale visual communication. The first person to ever report the effects of a light emitting diode was researching another form of communication. In 1907, a man by the name of H. J. Round was researching radio waves for Marconi Labs. He was using a device called a cats whisker detector, which no, does not contain any cats or part of cats. Round was searching for a sweet spot on a crystal silicon carbide when he noticed something odd. Part of the crystal started to glow, it lit up a pale yellow, and that was an LED. H. J. Round's crystal experiment was so cool and simple that I had to try it myself. So I got a piece of silicon carbide, then I hooked that up to the positive lead on my power supply. That's an alligator clip. I hooked a little sewing needle to the ground on my power supply. Then I began to search for light emitting zones. I built my own sort of cats whisker detector in order to keep the needle in place on a particularly bright spot I found. Now I can sit back and enjoy the warm glow of a homemade LED anytime I choose, even though it's pretty dim, but it's still cool. As far as we know, Round's research into light emitting crystals ended here, which is a shame because he was definitely on to something. But of course that's not the end of the story. Fifteen years later, in imperial Russia, a scientist and inventor named Oleg Vladmirovich Losev noticed that certain diodes in radios started to glow a bit when in use. Losev conducted a lot of heavy research and published his findings in several languages. But, sadly, they seem to have gone unnoticed. It wasn't until 1962, that a visible light emitting diode was made practical by Nick Holonyak working at General Electric. He's widely known as the father of the LED. The technology that Holonyak brought to the public is remarkably similar to our crystal experiment. A thin metal wire connects one side of the circuit to a small piece of semi-conductive material on the other side. The LED's two leads are cut to different lengths to show you how it should be connected. The longer is called the anode, and that connects to positive. The shorter is the cathode, and that goes to negative. To power an LED, you can just use a simple coin cell. This is a CR2032. And just make sure the longer lead is on the positive side, which is wider and smoother, and negative is on the other. If you plan to use a battery, let's say a nine volt, you'll also need a resistor to limit the current so we don't burn out the LED. Connect negative to the cathode, the shorter lead, and we'll put a 470 ohm resistor between the positive battery and the anode. For more useful info, check out the LED Center, and there's a lot of great history at the LED Museum. For all types of project ideas, info, and inspiration head over to Makezine.com.

Channels: Education & Instructional  

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