Voltage drop is
usually 1.9~2.1V for AlGaInP, 3.1~3.5
for InGaN and 1.2V for Infrared.
Current is usualy 20mA, for UFO LEDs current is: 30mA for InGaN and 50mA for
AlGaInP.
Supply Voltage - depends what you have
at disposal. Usuall is 6V or 12V source.