Red, Yellow, Green and Orange Led's works on 1.8 to 2 volts, White, Blue and Purple need 3 to 3.5 volts for proper operation. All 3mm LED's operate on 20ma except 3mm Flashing that work on 10 ma, A current limiting resistor should be used when lighting LED's in most applications. To find the correct resistor subtract led working voltage from your source voltage then divide by .02  for 20ma and .01 for 10ma, use a resistor equal to that amount or greater, do not use a smaller resistor. If there are any questions we are always more than willing to help if possible. 

3mm Diffused LED's