LED drive technology

There have two way to drive that led, may divide into resister currently limiter and constant current.

The resister limit current is one way of drive technology. the led has advantage of design simply and low cost . but it has a lot shortcoming:
*the current will change along with differ input voltage or forward voltage. for this result ，the indeterminateness of the led light produced by differ input voltage.
*the low efficiency: the drive efficiency are generally very low on high battery voltage drop. the reason for this is that most of power consumed in resister. the acquisition of heat is certainly result. so the dispel heat is big problem for resister currently limiter.

Other way is constant current source . is has advantage of current constant. but the price of constant current source is high than resister currently limiter.