I agree with GNRPowdeR.
In a normal non-LEO/military situation there are too many legal disadvantages to having a weapon mounted light.
Just carry the light seperately. That way you won't have to point a loaded firearm at someone who you aren't legally justified to shoot (which is a felony) just to use your light.
I'd like to hear more about cases where a weapon-mounted light created a disadvantage to the defense of an otherwise "good shoot".