I had "Transitions" briefly. The UV coating, etc. in windshields really is not the problem with "Transitions". Even if you are in FULL sunlight wearing a baseball cap, or similar cover, the glasses will not darken. In the cockpit, or in your truck or automobile, with a roof over your head, they will NOT darken. The glasses MUST "see" DIRECT sunlight to fully darken.
"Transitions" are NOT like the old "Photo Grays" that would react to scattered light and darken, even on cloudy days. Even Photo Grays, or Photo Gray "extras" are not a real good substitute for real sunglasses.
"Photo Grays" work pretty well but are only available with GLASS Lenses which are heavier than plastic ("Transition") lenses. Clip Ons, or Real Sunglasses are the solution.