mosfet led driver

this led driver uses a constant current circuit using N-channel power mosfet. What this driver do is it delivers constant current through the LED thus protecting it from damage and at the same time maintaining the output power and output light of the LED. The magnitude of current is controlled by R2 and the voltage of base-emitter of transistor Q1. In equation form:Current(in LED) = 0.7/R2 or R2 =0.7/Current; where this current is the operating current of the LED.

Part List:
R1- 1 kilo-ohms resistor 1/2W
Q1- 2N2222 NPN transistor or similar
Q2- IRF530 power mosfet, or similar
DC- 9V to 15V DC
See values of R2 on every LED current and power rating in resistance table below. R2(actual) is the value used in actual circuit.

http://www.simple-electronics.com/2011/09/high-current-led-driver-using-fet.html