Story speaks for itself - BBC News - Costa Concordia cruise ship captain 'went off course'
I don't care if it's the biggest ship on the ocean with the most lights per square foot or a small sailboat like a Sunfish, having a light when the lights go out or if you fall over the side or whatever may save your life.
Doesn't have to much of a light, either.
Even carrying a couple of glow sticks in a pocket or purse is a good idea if you won't carry anything else.
They will help you find your way out of dark spaces and help rescuers find you.
Glow sticks are cheap. I always carry a supply in my car. You just never know.