[C3H8]

I use to be a lab technician at an optical. i ground plastic and glass lenses to fit people's vision perscription. part of this process is making sure the glass or plastic lenses had at least 94% uva and uvb blocking capability. we had a nifty little machine which shine a special uv light and you would hold the glass or plastic eye glasses lens in the light. there was a sensor behind the light, and the lens, which measured how much of the uv was blocked or absorbed by the lens.

most of the time it had to block at least 94%, as i said. if it did not meet this criteria, we had special liquids which we could immerse the lens in, under about 180 degrees of heat for a period of time to increase it's uv blocking capability.

standard cheap cr-39 plastic lenses which most people have in their eye glasses do not naturally block the uv rays. they have to be immersed in that chemical i mentioned for about 10 minutes to build up enough of the chemical to block the uv rays to an acceptable level.

polycarbonate lenses which are used in all safety eye glass lenses as well as childrens glasses naturally block uva and ubv rays to near 100% according to the machine i had.
a 1/8 sheet of polycarbonate from lowes also blocked the various uv rays to near 100%.

glass lenses used in eyeglasses naturally block uva and uvb rays to near 100% as well.

a few things i learned from this nifty machine was that uva and uvb are naturally blocked by the glass used in eyeglasses without any special coating or films. being the curious as a cat type, i "borrowed" the machine one weekend and took it home to test my car glass and my house's windows.

what i found was that the car's rear and side windows blocked more then 94% of the various uv rays. the windshield blocked nearly 100% of them. this is not surprising since the windshield of most cars is laminated with some sort of plastic, i think polycarbonate?!?!. some one correct me if i am wrong on that.

adding just a few percent of tint to a car's side window resulted in near 100% uv blocking. adding limo black like i currently have on my car did not increase the uv blocking by much since you cannot block more then 100% when 100% is all of the uv rays. but limo black seems to greatly decrease the time it takes my hot ass interiour to cool off during the day when i get in the car and its scalding hot inside.

so to re-cap,

car glass blocks most of the uv rays right off the showroom floor with no tint at all.

windshield do it even better even with no tint.

adding dark tint somehow helps keep the car drastically cooler

its good to "borrow" things.

and yes i got fired from that job... you figure out why.