LEDs, of any size or shape, are quite easy things to work with once you know a few basic things about them, and about electricity.
LEDs are, basically, a bit like normal light bulbs. You pass electricity through them and they glow. If you pass too much electricity through them, they die. There are some important differences between LEDs and incandescent lamps, though.
First, LEDs are diodes, so they have polarity; they only work one way. Ordinary LEDs (not Luxeons, or tiny surface mount LEDs) have a long leg and a short leg, as they come from the factory. The long leg of an LED is the positive one. If you connect the thing backwards, it won't do anything. It won't be hurt, either, though, unless you apply rather more reverse voltage than the LED normally runs from. Anyone who's assembled a computer and connected the case LED plugs backwards will know this already.
 
Second, LEDs need some resistance in series with them, either as part of the power source (if it's a small battery, for instance), or as a separate resistor. This is because LEDs have a death wish.
Incandescent lamp filaments have a positive temperature coefficient of resistance; when they get hotter, their resistance rises. They get very hot in normal use, and their resistance is much higher then than when they're turned off. Like, more than ten times as high.
LEDs aren't like that. They've got a negative temperature coefficient of resistance; the hotter they get, the lower their resistance becomes. And they warm up in normal operation - they're not magic 100% efficient electricity-to-light converters, but waste some power as heat, just like everything else.
If an LED is already passing enough current that a bit more power dissipation will kill it, and there's nothing - like a series resistor - to stop the heat-related resistance drop from allowing the LED to dissipate more power, you've got a situation called "thermal runaway", and your LED is not long for this world.
Overdrive an LED relatively gently and it'll briefly emit colours rather higher in the spectrum than the one it's meant to produce, and then die, with a very small sad sizzling noise. The thing you are left with after this may be referred to as a "friode".
If you overdrive an LED brutally, it'll still end up as a friode, but it will in the interim briefly function as an SED, or Smoke Emitting Diode.
Ex-SEDs are always open circuit - they don't pass any current - but more gently killed LEDs can end up short-circuited, which is worse. When a shorted LED is in a series string with other LEDs, they get to see all of the voltage that was meant to supply the whole string. This, of course, accelerates their own death.
If you REALLY, REALLY want to know all that there is to know about LED's visit Wikipedia at:
http://en.wikipedia.org/wiki/Light-emitting_diode
They have an amazing reference section on LED technology including a comprehensive history of LEDs.
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