LED Resistor Calculator

There are many sites that have simple calculators for LEDS and resistors

here is an example of one I find useful

http://ledcalc.com/

1. Typically, we use 14v for the supply voltage. The normal DCC HO scale track voltage
2. The LED voltage drop should always be 3v or less unless specifically stated otherwise by the LED manufacturer.
3. Desired current should be as low as possible for your brightness level needed. Start with 10 mA, adjust up or down as needed but never exceed the rating of the LED!
4. The more current you draw the brighter the LED gets BUT the resistor will be larger in size and / or warmer too.  Tradeoffs are involved here so some experimentation is needed.