Only my own anecdotal study here. It's not total darkness, because I'm in a well-windowed cube farm (along a far wall that has no windows, though), so there's still a bit of ambient light.
I always tell people that if it's worth memorizing because you use it a lot, you'll probably memorize it because you use it a lot anyway. If you have to make a point to memorize something, it's a hint to consider if it's worth the time.
Similar here - my cube is as dark as I can get it (which really just means the lights directly overhead are off), and my monitors are at the minimum brightness setting. My screens glow, guys. I don't need to light them up externally.
And if Ebola got loose around here, I guess I'd do that then, too.