Metallic tint films (and just about all the good ones are) will decrease detector performance, and any tint will decrease lidar detection performance.
Not that it matters much on our trucks, which already have the radar cross section (RCS) of a small office building, but tints can increase the RCS as well -- meaning the radar gun will get a return signal sooner.
I still miss my old '94 Probe GT. No headlamps, no front license plate, no chrome to speak off, black, and swoopy. The late Don Schroeder (who was Car and Driver's senior tech editor) and I determined the effective lidar range on that car was about 3 feet. /ubbthreads/images/graemlins/smile.gif Radar was another story, but with the Val1, I could see 'em before they saw me.
Interestingly, though, the bulk of our trucks actually works in our favor -- visually, unless you're passing everyone on the road, something that big doesn't look like it's moving as fast. For a big example, look at a 747 and a small business jet when they're coming in for a landing. The 747 will appear to be moving slower than the bizjet, even though they have similar landing speeds.