I was in traffic court a few years ago waiting for a case to be called. There was a state trooper ahead of me. He had several cases on the docket for illegal tinting. He would eyeball the cars and make his own determination about whether the tinting was darker than permitted by state law. If he thought it was too dark, he pulled over the car and tested the tinting with a light meter. Some of the defendants were acquitted on the illegal tinting charge, but they were all subject to a traffic stop and all the things that go along with that. Kind of scary.