They have you close the curtain at night because the bright light from the cabin ruins the night vision of the bridge team since the bridge is rigged for black at night so they can see. Ever notice when you're outside in the dark and you're able to see fairly well, and then someone turns on lights and you can't see anymore? Same thing here. I guess the naval architects didn't think that one through too well when they were designing the ship. When I was in the Navy on submarines, the ships control party would often wear red goggles at night when the lights were on in the control room so in the event we had to go to periscope depth, when we turned off all the lights, our eyes were already adjusted to be able to see in the dark since red light doesn't negatively effect the ability to see in blackness.
