I would like to light up a 2 W LED with a 3.7 V power source in the most efficient way possible. The Vf of the LED is 2.4 V. Is there any way I can reduce the voltage to 2.4 V from 3.7 V without using resistors as with a required current of 350 mA, the power wasted as heat in the resistor is too high. I am looking to find an easy way of accomplishing this as the circuit has to be used in a low cost device that needs to be efficient and cheap.
If you want to do this efficiently then you need a switching power supply. However, LEDs should be driven with a constant current rather than a constant voltage, so you need to build a switching current supply specifically designed for LEDs.