Direct current drive circuit is not controlled, when the battery voltage is high enough, when the battery will do our best to supply the required LED, a start will be very bright flashlight, the temperature rise in vain, heating and cooling can not be balanced. After the battery is running out of brightness and temperature will slowly drop, this circuit due to pre-charge is too high, the LED and battery damage is very large, lED of life often can not meet the design life, the battery life will be because of work overload shorten. This "quick success" driving scheme is not limited stream, only the low end of the flashlight will be seen. For long-range sense, the early long-range effect on the flashlight will work better, as time progresses, long-range capability will rapidly diminish.
Constant drive current, the current mainstream driving scheme. LED current supply circuit will be controlled, so that current is always maintained at the same size, for example: XM-L T6 uses 2.0A constant current driver, maintained at 700 lumens brightness. After constant current, heating and cooling flashlight is also balanced, the output current of the battery can be maintained unchanged. This is the optimum drive solution. Usually small size flashlight about 15 minutes you can strike a balance. Long-range effect can be maintained consistently.