Bought new Christmas lights L.E.D how do they work?

The kids asked me how they give off light if they are not a bulb. They stumped me..... Help.
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wrote:

lite-up.
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The really simple explanation: A light emitting diode is a solar cell working in reverse.
Why they are colored: This "bandgap energy" business about semiconductors. The light they put out is of wavelength close to or maybe somewhat longer than the longest wavelengths at which they can work as a solar cell.
If you put an LED on a microammeter and have sunlight hit the LED, youmay get a reading. You will not get much, and one reason is that the ship is so small that only a tiny amount of sunlight will be collected by the chip.
I believe regular solar cells will put out a bit of infrared if you push a DC current through them in reverse.
- Don Klipstein ( snipped-for-privacy@misty.com)
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gary wrote:

http://electronics.howstuffworks.com/led.htm
http://en.wikipedia.org/wiki/Light_Emitting_Diodes
Electrons, mumble mumble, quantum energy levels, mumble mumble, state transitions.
Contrary to comments that LEDs require DC, I think you'll find that the cheapo Xmas lights work on AC, and simply flash on an off as the voltage alternates. You can prove this by waving a bulb rapidly in front of your face and seeing multiple discrete images. (Unlike incandescent filaments, LEDs turn on and off almost instantly, so the light doesn't ride through the AC voltage cycle.)
Mebbe they rectify the AC and give you 120 Hz, or maybe they don't so you get 60 Hz. A DC power supply to provide constant light would negate the cost savings and reliability of the simple solution.
Chip C
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Thx

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Light is just an atom's way of screaming. When you pump electricity through a fillament, it gets really hot, and the atoms start screaming. The chemicals burried in the middle of a diode are just a lot more excitable than tungsten atoms, so they get all excited by just an electric shock.
.
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gary wrote:

All atoms have bands of electrons circling the nucleus. When you excite these electrons, by heat or by electricity, the electrons jump to the outer bands. It takes energy to do this. When the electrons return to their normal band they shed that energy in the form of photons (i.e. light) The difference in bulbs and LED's is the energy source to get the electrons to move. Bulbs require heat. LED's are made of atoms that easily get the electrons to move with low voltages.
Bob
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Well, they ARE a bulb. Incandescent, fluorescent, LED. Different types of bulbs.
--

Christopher A. Young
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