I have routinely observed that UV does not penetrate into our cars and homes from outside, and one simple method to confirm this is with Transition Lenses which remain clear in this situations.

I noticed the other day that my transition lenses were ~half tinted while flying in some sun inside my air conditioned LIVP at FL210, so UV must be penetrating the thick acrylic canopy material.  This is not the case inside a car.

Being a fair skinned irish-german, I slather 85+ SPF Neutrogenia lotion on regularly and daily, but always felt that inside the cockpit (or car) that my exposure was minimum.  This suggests that long flights might justify reapplication of sun block.

Manufactures of acrylic canopies can choose to add UV filters to enhance the filtration above 300nm.

Just sharing an observation to my fellow Lancair pilots.

Jeff L

http://en.wikipedia.org/wiki/Poly(methyl_methacrylate)