I know every situation is different.
The one time when people entered my home illegally, in the middle of the night (3 am actually). The first thing I did was get my shotgun. The second thing I did was turn on the hallway light.
Why turn on the light? I could have just shot them in the dark, right? There were two other people living with me and I wanted to know for sure that I was pointing that 12 gauge at the uninvited guests and not one of my roommates.
I challenge anyone in the "shoot them in the dark" side of this argument to show me two reputable defensive shooting schools that advocates against the use of tactical lights.
"9mm has a very long history of being a pointy little bullet moving quickly" --Sevens