halocline
Contributor
A blackout mask solves that problem in a hurry. Since many drills revolve around limited viz, putting on one of these makes the clearest water a total blackout. I picked up a pair of neoprene blackout masks that I carry in a pocket on open water dives in case anybody wants to play.
I'm pretty sure pfcAj was not talking about zero visibility, he's talking about general ambient light. You generally wouldn't be running a line in zero vis. (other than a safety line in an emergency) I think he's referring to running a line, planning tie offs, etc, in low light situations where you need your light rather than sunlight. The best way to simulate that in OW would be to simply go at night.