As a diver, I can tell you one thing:
We went out to a night dive once, in a coastal area. It was a quite shallow one though, about 15 meters max depth.
And believe me: without your Floodlight you were NOT be able to see ANYTHING down there.

I'm talking about your Hand in front of your face for example.
What I would love is to have dynamic shine in SH3, so that DC explosions light up the ocean and the exterior of your boat at night for a short time.