You have a valid question there about why the white lights were on durring the day. I suppose it's the same reason - no point to stay in the dark in the sub to be temporarily blinded by strong light when you get out... Or have to wait for minutes to accomodate with the dark if you go into a crash dive...
I think in real life white or red lights would have been used more liberally... If you watch Das Boot (which is no actual reference to how it was but close enough), some quarters kept red lights, some kept white lights no matter whether night or day. It comes and goes with the teritory - if the torp crews needed more light to arm the eels they probably kept the white lights and doors locked while the command room would keep red lights for a periscope search.
Actually, even red lights would not be sufficient to do a night-time periscope search, the captain would wear full-black googles for a few minutes before looking through the scope - again to be witnesseth in Das Boot
