ooooohhhh boy here we go.
i would think in war time it wouldnt matter in the daytime and just take a average watt light bulb or look it up on google to see what kinda lightbulbs were used in subs and see what their respective candle light power was and go get one close to that and turn it on in a dark room and sit back for awhile and let you eyes adjust to it and youll get your answer. but i do know that at night they used the red lights as to not mess up their night vision if you were going up and down between the conning and the command room.
