If you want to preserve your night-vision and all you have is a bright mag-light, hold it above your
head like a torch, shine it on the ceiling and get around in the reflected light. The bright spot on
the ceiling will light the whole room with a dimmer glow.
Personally, I prefer a red LED headlight; it's compact, has a headband to keep it from rolling off
the night-stand, and it REALLY preserves the night-vision.
I like a really dark bedroom; my digital alarm-clock spends the night face-down because the
display lights up the room. I've even had to cover the microwave-oven clock in the kitchen to
keep that blue light from streaming in.