Yes we never turn 'em for takeoff, as per SOPs. I don't think it really makes a difference to peoples night vision, considering you've just taxied with 'em bright and you're going to whack 'em back once airbourne. That momentary darkness will hardly give you any see-in-the-dark abilities, certainly very little above what you would have had before. It takes eyes alot longer than a couple of seconds to adjust.