I just ordered some LED's for 2 of my tanks and I want sure what size resistor to get. I have ordered 390mcd lights that are 3.5v, what size resistor would bring that to a nice brightness? I was thinking 470-Ω 1/2 watt with 5%????
Here is a resistor calculator that I used for my moonlights. All you need to know is how many LED's you are using, and what your source voltage is.
I would recommend testing your source for the actual voltage, as my 6V transformer actually put out 10V!!