I've got to agree with the advice from chaosmagnet. If you can't get some actual training/trigger time under low-light conditions there are some good videos (some really bad ones too) and that may give you some ideas. Find someone who actually knows how to use a light and handgun and work with them is the best bet.

I have trained with the 'harris' technique, the old fashioned FBI style and several others but you need to find what works best for you and your situation. I've got a light mount on the long gun but not on any handgun. However I always have a light with me. I got a purpose build extra mag holder that included a slot for my surefire flashlight and when asked about it I always maintain I would much rather have the light and one extra mag than two mags and no light.

EDIT: I forgot an important factor - from a cop's standpoint, a weapon mounted light equals pointing a weapon at what ever you want to illuminate - a light independent of the weapon lets you light up anything without also making you point a weapon at it too. Having both may be the better plan.

I got the original surefire back in the day (expensive but I was betting my life on it)and it was amazing - 100-160 lumens to light up the area or a 'bad guy' night or day - there are a lot of dark places inside even in the daytime. Right now my primary light kicks out 1800 lumens and I like it a lot. YMMV. Find something that works for you and practice with it.

Paul -