Will it make my rooms look darker?

Darkness is very subjective.  If you walk into a previously tinted room, you may not even notice the tint at all.  A film that reduces 50 or 60% of the visible light, does not darken a room by the same 50-60%… only about 20% darker.

It is like wearing sunglasses and going outside.  You are more comfortable and after a few minutes you forget you have them on.