I can tell you that, after riding a motorcycle on the same roads, a blast of sand particles hitting your face at 50 is a lot less painful than at 80 
Back when all lensās were glass we didnāt have this problem, because glass is much harder and less prone to abrasion.
My theory is that the ones that do haze up and stained are just not as good a quality of polymer than the ones that go 15 years without any noticeable effects.
Iām sure it sand and dust in the air that beat at the lens and eventually scuff it enough to make it hazy and the microscopic scratches keep us from really cleaning them well.
The lacquer works pretty good, but to do it right you have to buff them out also. I just took mine out and rested them in my lap as I buffed.
Yosemite
Not as painful as this, TTā¦
Yosemite
Iām not saying that some good things donāt start out as a late night TV ad, but Iām always a little skeptical.
I always figure if the products pitched on TV (not available in stores!) are any good, then theyāll turn up at Walmart for half the price pretty soon.
Iām sure it sand and dust in the air that beat at the lens and eventually scuff it enough to make it hazy and the microscopic scratches keep us from really cleaning them well.
But then the highway-driven cars would be consistently worse than the sit-around-towners, and that doesnāt seem to be the case.
Yosemite, Iām no plastics engineer, but I do suspect that there are variations in the basic polycarbonate, just as there are variations in the purity of glass, and there may even be variations induced by variables in the molding processes. In addition, polycarbonate is known to not have good scratch resistance, and manufacturers add a surface coating, which Iām sure varies as well.
Beyond that, environmental stresses such as UV vary tremendously with different operating environments. A variable in the operating environment is also, Iād guess, the laminar flow characteristics over the lens.
I donāt know that heat per-se affects the polycarbonate or the coatings, but if thereās a polymer engineer in the house whoās familiar with this Iād sure appreciate the input.
One thing I find interesting is history repeating itself. Back in the early days, automotive headlamps were housings with lenses and separate bulbs in them to provide the light. Then they eventually evolved to sealed-beam lamps. Now weāre back to lenses with separate bulbs in them.
I wonder what would happen if clear fingernail polish were applied to a hazy headlight?
If it attacks the polycarbonateā¦ what will happen is that youāll be a few hundred bucks lighter after replacing the modules. But I use MaGuireās (sp?) carnuba wax on mine without a problem.