Cockpit window Sun Shade

[1-26E]

UV windshield blocking

This site Ultraviolet radiation indoors: What you don't know can hurt you. has the following information. Don't know if it specifically applies to aircraft windshields but it would seem to explain some of the observations here.

In the modern world, people are spending ever greater portion of their time in cars. This trend is likely to continue unless rising fuel costs and/or global warming bring about major changes in our transportation habits.
In the majority of modern cars, the windshield is built of laminated glass that blocks all of UVB and the vast majority of UVA. However, the side and rear windows are usually made from non-laminated glass and let much of UVA through. Clear non-laminated car windows allow up to 60-70% of UVA to penetrate. Tinting reduces UVA penetration to about 15-30%, a much better but still significant level.
If your car has clear glass windows, you can add tinting at a qualified auto shop. However, make sure the facility can guarantee compliance with the federally mandated standard of 70 percent of minimum visible light transmittance through the windshield.
There are other factors influencing UVA exposure in the car: you position (the closer you are to a non-laminated window, the greater the exposure), direction of driving relative to the sun, time of day/year, etc. However, people rarely have much control over any of these. Therefore, you should still use sun protection measures while in the car, such as sunscreens, protective clothing, and so forth.