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I would like to know more about the properties of LED's. Voltage, output and the like,but most of all where to buy them. Most of the websites I've checked so far only sell a complete string, bulb for home and such.

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cheapest place to buy them is ebay, like 6-8 bucks including shipping from hong kong for like 100 with free resistors.

LEDs work off any voltage above their voltage drop voltage, and are usually as follows:
red: 1.7v
green/yellow: 2.1v
white/blue: 3v

This means that you could run an LED off fo 1,000,000 volts with no problems (well, besides the electricity arcing over the physical leads and catching the whole thing on fire :P) as long as you limit the current as follows.

their brightness depends on the current being fed through. Most LEDs use 20mA for full brightness, and 30mA max current. NOTE: even 5mA through an LED is pretty bright! It's not a linear relationship

lets say you have a 5v powersupply and you want to light up a red led at 20mA, you also need a resistor in series to drop the voltage and limit current
you can either enter it into an online led calculator, or use the formula:
(power supply voltage - LED voltage drop)/current
so for our example:
(5 volts - 1.7 volts)/0.02 amps (aka 20mA) = 165 ohms for the resistor. because that's non standard, it's suggested to round up to a common value, like 220 ohms. The brightness will be about the same

anymore questions?

The only thing to really add about leds are they are in fact just diodes...that happen to emit light Learning how diodes work in circuits really helps understand what all of the above means... the addage that 'any voltage is okay' is a bit of a misnomer - as the led itself must never be subjected to such voltages themselves - the 'current limiting' resistor in the basic linear circuit does drop the voltage within the range needed for the led. Overvolt the component and you will destroy it.

Regarding, the question of where to buy discrete LEDs:

The surplus sellers are usually the cheapest, places like:

http://www.goldmine-elec.com/
http://www.bgmicro.com/
http://www.allelectronics.com/

If they don't have what you're looking for, try the retailers that sell new (not surplus) components, e.g.

http://www.jameco.com/
http://www.digikey.com/

This list is of 5 urls is by no means comprehensive, but these are reliable companies that I have bought parts from in the past. All are located in the former US. Not sure if that's relevant or not. Obviously if you live in Uzbekistan, or Tibet, or somewhere like that, the shipping might be expensive.