0dalucero 12 years ago 11010010110 is right. Use that link. You need to limit the current flowing through the LED. Figure out what your LED's safe operating points (forward voltage, current) are and go from there. 5 volts is probably not enough to power three LED's in series so you'll have to put them in parallel. Putting 5 volts across an LED will likely draw too much current for the LED to handle and it may burn out or worse. Putting a resistor in series with the LED will drop the voltage across the LED allowing a safe amount of current to flow while still lighting up the LED. Pick a resistor value that drops the LED's voltage down to what the LED's spec sheet says for a typical forward voltage.