This may or may not happen often but I've ridden it once with ALL of the lights completely turned off and that was awesome! What I mean is that all the projections where off, there weren't any 'stars' or the galaxy projection. It simply was pitch black and you couldn't even see your own hand in front of your face! Although it's always dark when you ride there is still plenty of light to see the track in front of you and what is coming up next and you can make out other trains passing as well. But with it pitch black it certainly made the ride feel bumpier and faster than it really is.
I went on the ride one morning and they must have not turned on a few of the star projectors, because there were a few points in the ride where it was just pitch, like ascending the third lift in utter darkness, and it got pretty dark near the bottom.