Can I reduce voltage of an led?
LEDs like all diodes have a voltage characteristic that is defined mostly by the materials used to make up the junction. This is referred to as the forward bias voltage often notated as Vf. You can vary this voltage a little by controlling the current you feed the LED but for the most part diodes like to set their own voltage when fed a current within their recommended operating range. Feed the LED less current and you will operate it at a slightly lower voltage.

Some quick points:


Less current = less brightness and lower voltage (too little and it won't turn on at all)
More current = more brightness and higher voltage (too much and it will pop)
Look at the datasheet for a given LED and find the graph where it shows it's current to voltage relationship.
Put a resistor in series with your LED (more resistance = less current and voltage)
White LEDs require the highest Vf to operate followed by blue followed by blue green. Red and yellow LEDs can operate at lower voltages.