There are two characteristics to consider, flood and throw. Any light worth mounting will have a reasonably wide beam (flood) while still throwing the beam far enough to be useful.
Keeping the weapon safely and correctly at a low ready, correctly pointed in front of you (hopefully it's already obvious how important getting some decent training is), activating the light will throw a wide enough beam to see if anyone inside a regular household-sized room is a threat- without ever covering them with the muzzle of your weapon. The only time this will not be true, is if the potential threat is so close that your light beam has not had time to expand. If this is the case, you have no clue how to clear a room, because you have moved into a position right next to a blind spot, close enough to have your weapon grabbed and deny you the main advantage of a firearm (distance).
Training and experience- get 'em.
John
Keeping the weapon safely and correctly at a low ready, correctly pointed in front of you (hopefully it's already obvious how important getting some decent training is), activating the light will throw a wide enough beam to see if anyone inside a regular household-sized room is a threat- without ever covering them with the muzzle of your weapon. The only time this will not be true, is if the potential threat is so close that your light beam has not had time to expand. If this is the case, you have no clue how to clear a room, because you have moved into a position right next to a blind spot, close enough to have your weapon grabbed and deny you the main advantage of a firearm (distance).
Training and experience- get 'em.
John