KB1LKR,
you said:
For example if you have 12V, an LED that requires 20mA w/ a junction drop of 3.0V then you need to get 20mA at 12V-3V=9V of drop across your current limiter so you need a 9V/0.02A = 450 ohm, 1/4W or 1/2W(9V*0.02A=0.18W) limiting resistor. A 470 ohm would be close enough.
Thanks - that's exactly what I needed! It is indeed a 12V bulb in there now, at 60mA, but the white LED's from R$ are 3.6V @ 20mA
Much appreciated.