Let there be light?
Unless you live in a cavernous warehouse, turning on a high intensity rail light will provide sufficient reflected spill to illuminate the entire room you're in. Experienced, prison-trained thugs know to shoot once to the light and once to either side of it.
I don't use a rail light. Instead, I leave small lights on which provide sufficient light to eliminate total blackness and to allow me to differentiate friend from foe without a bullet magnet (flashlight) in my hand. I also practice low light shooting.
Also, conducting sweeps for that bump in the night is a surefire way to get yourself ambushed and shot in your own home. I feel that having a rail light will give you a false sense of security and cause you to use poor tactics. The companies that make them don't tell you that because they are in the business of selling lights, not tactics.
Int'l Assoc. of Law Enforcement Firearms Instructors