Some very interesting concepts!
What camera are You using? Any UWflash as well, or are You using a flaslight?
I`m using a g10 canon with canon housing.
Most of the shots are iluminated by an independent dive torch that I hold with my hand on the side (MB SUB - BASE. It is a 20W halogen HLX), so I can light only the part that interest me, but many times I mess the shot be cause I move a bit or I need both hands to change some of the settings in the camera.