I started writing this for another thread, and I thought I should start a new one so that others could refer to it in the future. This should unravel the mysteries of the LED for a few and give a little more direction for their use.
I just wanted to add a note about LED's, they will work without a resistor, but it really is better for them if they have a resistor inline and they will last their intended life. A little bit about LED's, for those who don't know, LED stands for "Light Emitting Diode" what this means it that the function if it is to let current through one way and not the other. Think of it as a one-way valve, and as a byproduct, it gives off light. Of course these diodes are engineered specifically to give off light.
On the circuit level, they "read" as a switch. Think of it this way...
-Disclaimer- Now this is only an example for dramatization "don't do this at home, ever!!!!"
Take jumper cables to your car battery, put one on positive and one on negative; the other ends put on a standard 12v light automotive bulb, one on positive and one on negative - instant light!!! - For an LED, take the bulb out and replace it with a switch; put one on positive and one on negative; switch it on, "BAMM!!!" SHORT CIRCUIT...
This is how the LED reads in a circuit, the resistors purpose is to act as a load so the circuit reads correctly, not a short circuit. "Well, that sounds fine and good, but what value of resistor do I use???" Well, you use the formula to calculate it (Great... math...)
10 easy steps to LED resistor value identification
1) You take the voltage, 9v in this case.
2) Take the LED voltage drop (this means how much does it use up) easy, it
states it on the package!!! For white LED's probably 4v.
3) Subtract them!!! 9-4=5 Easy so far, right?
4) Take the LED current rating (it says this on the package too)
for White, to be safe we will say 20mA which is .020A but it can be
5) Divide the two 5 /.020 = 250
6) Resistors come in standard values so pick the nearest standard value
which is greater, for us it will be 270 ohms.
7) The resistor % just means how accurate it to the stated value, 5% or
10% is fine, what ever you can find.
8) The wattage is for how much power will go through it, so anything small
1/4w or 1/2w is fine.
9) HOOK it up! It does not matter what side the resistor is on. It
It does matter what side of the power the LED is hooked up to, the long
lead on the LED is ALWAYS positive. (unless someone cuts it!)
10) Enjoy your lighting!!!
I hope this helps explain a little more about this lighting product, and makes it easier to install your LED's for your projects.