Check out the pics in my gallery. I have 5% on the back window of my roadster, and 20% on the sides. As you can tell in my pictures, the sides look pretty dark. In shade or at night it's basically like looking at limo tint (5%), but when it's sunny out or when the sun is directly hitting it, you can see in the 20% pretty well.

As far as looking OUT of 20%...I've had it on all my cars and never had a problem with backing up at night. I love it.