There seemed to be a few light with invisible sources that would either hurt or heal you. Such as the first two at the start of the game. I couldn't really visibly tell much of the difference between the two of them.
I think some of the pressure plate buttons where a little hard to spot once the lights where extinguished. Perhaps if in the dark that had a little bit of a glow to them similar to that of the exit level cylinders. Though I just might be dump and spent a minute or two not noticing one of them.
Other than that I really enjoyed it!