Originally Posted by martini
I'd add to that, the further aft you position the light source, the more of the boat is going to get lit up. This is going to make it all the harder to see anything outside of the boat.
And I would add further still. By the time you add in some light being thrown back by very shiny salt spray, it is too easy to stop your eyes getting accustomed.
On night passages I have even found myself transfixed by the reflection from the nav lights in the foam either side of the boat, better to keep the light low and your eyes on the sea.
As already said if you need light for coming into shadowy marinas then a handheld is a better bet, easier to stabilise on a rocking boat too.