Current limiting resistor
led - Leds
in series - Leds
From molex; 5, 7 and 12
Typical LED forward
Ordinary Red LED: 1.7 Volts
special red high-brightness, high-efficiency, or low-current: 1.9 Volts
Orange or yellow: 2 Volts
Green: 2.1 Volts
Bright white, emerald green, and most blue-derived (phosphor): 3.4 Volts
430 nM bright blue: 3.5 - 3.8 Volts
U.V: 4.6 Volts
If you are unsure on the current try 15 mA.
For blue, white, and exotic colors try 10 mA.