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.
Thanks, federali. That pretty much sums up the unease I mentioned earlier when I said that rail-mounted lights were a device I was wary of. Far better to have some night lights placed around the house, and a complete knowledge of every square inch of the place. I do a lot of low-light practice with my CT grips when I go to the range before sunup as well.