Welcome to Resistors 101

Resistors are measured in ohms. The higher the resistor value the more resistance meaning the dimmer the LED/Bulb. Like wise it is also flip flopped; the lower the resistor value, the less resistance, means the LED/Bulb will be brighter.

The colors on the resistors help to identify the value of the resistor. I attached a photo of the back of resistor pack from RadioShack. Lets go over an example of a common resistor for LEDs, 470 ohms. The colors for this are Yellow, Violet, Brown.

So, using the package the first band is yellow which has a number of 4. The next band is Violet which has a number of 7. The third number is brown which has a number of x10. So put the first and second band together and you get 47. Then take 47 and multiple it by the third band, so 47x10= 470 ohms.

The fourth color is usually gold, sometimes silver. This is the tolerance of the resistor. I usually use gold band resistors at 5%.

Now we'll switch to Resistor 102, figuring out the value you need.

This is where Ohm's law comes into play. R=V/I R=Resistance, V= Voltage Difference, I= Amps. Follow along as we figure out the Resistance. I'll be using your track power and LED's.

R= (12-3.2)/.02 12 is the track voltage, 3.2 is the forward voltage of the LED and .02 is the amps for the LED.

R= 8.8/.02

R= 440 So a 440 ohm resistor is needed. Closest you'll probably find at Radio Shack is 470 ohms. Remember to go higher with a resistor value not lower. If you use a resistor below 440 you could damage the LED.

Now, to figure out what wattage of resistor is needed. This is W=V*I

W= (12-3.2)*.02

W=8.8*.02

W=.176 So a 1/4 watt resistor (.250) would be fine. If you were close to .250 or higher then you need a 1/2 watt resistor, .500. RadioShack sells both 1/4 watt and 1/2 watt resistors.

Hope this helps.