I have some (white) LED pucks that each run on (3) AAA batteries in series, or 4.5v. These are the kind of pucks that you would put underneath a kitchen cabinet, push on/off. Each puck has (3) white surface mount LEDs wired in parallel. I don't have data sheets available, and so I don't know the forward voltage drop for the LEDs, and also don't know how the equation changes when there are (3) LEDs in parallel. So the best I can do is measure the battery current thru the puck when using the (3) AAA batteries. The measured current is 62ma. I have a 12vdc power supply in the project (which powers other 12v things), which I am guessing should first be run through an LM regulator to get the voltage closer. I did do a test using 5v directly from a USB cable (no current limiting resistor), and I fried one of the LEDs. So, I know that I need minimally a current limiting resistor. Can someone help me calculate the value of that resistor?