Lights off. I'd secure myself and loved ones in the room with guns...but if one were to go out, lights off.
If you turn the lights on, bg identifies you immediately while he's still hiding in a dark corner. With the lights off you're able to paint the room with light without giving away your position. I'm no pro, just something I picked up while attending an ALERRT course on low light situations. Now if the house is wired so you can hit all the lights simultaneously, do that. Otherwise, walking from room to room to clear it and flipping lights on will make you an easy target for a bg hiding in the dark.