Ultraviolet Thought

[mishalak]

People spend a lot of time in cars they even get sunburns on long trips. Car interiors get a lot of damage form ultraviolet light as well, so why don't they put ultraviolet coatings on car windows?

Comments

Ultraviolet Thought

[vincent-d.livejournal.com]

Glass is opaque to UV - UVB, which causes sunburn can't get through glass, though some UVA, which cases wrinkling, does. You can get carglass with extra UV protection but really the only way to get a sunburn in a car is to drive a convertible with the roof down. :-)

Re: Ultraviolet Thought

[mishalak.livejournal.com]

I've actually seen a guy with sunburn on only one side of his face from a car trip. I'm pretty sure that something gets through.

Re: Ultraviolet Thought

[gomeza.livejournal.com]

He had his window down.

Re: Ultraviolet Thought

[alias-lilacgirl.livejournal.com]

Oh, the truck driver's tan! Where the left arm is always much darker than the other because he has it out the window all the time.

[scottscidmore.livejournal.com]

There's several reasons why not.

When you want to filter out UV, you use a number of methods to do so. The simplest is to use glass containing noticeable amounts of iron, which gives it a slight greenish tint, and to apply a simple coating to absorb the UV. That coating doesn't have a square edge from 100% to 0% transmission at 400 nm, it will be a slope from the maximum transmission to the minimum. This means that some UV gets through, or that you design the filter so it starts absorbing in the blue-green which makes stuff look funny when seen through the glass.

Getting a sharper edge to the absorption curve is increasingly difficult the squarer the edge; this also means it gets more expensive to manufacture. Some of the filters are also fairly delicate, both to scratching and/or destruction from moisture, heat, and so on.

So there's a trade-off between cutting out UV, affecting the visible light view, and cost.

Note that while cutting out UV will help protect the interior, even violet and blue light will cause some damage.


These folks talk a bit on it, offer a graph or two, and list cars that use their UV absorbing laminated glass.

http://www.solutiaautomotive.com/en/lgi/uv.aspx

[akicif.livejournal.com]

I'd be surprised if you really needed a filter at all - unless you're spending an awful lot of time driving in incredibly intense sunlight. When I was doing UV/visible spectroscopy, all the optics and the sample container had to be made of quartz to let enough UV through - even a fractional millimeter of ordinary glass would cut out a surprising amount.

On the other hand, when it comes to atmospheric UV flux, I'm more or less at sea level in grey, misty Scotland, and you're almost a mile higher and a lot further South.

Ah. An experiment.... You will need a handheld UV light, a car, a piece of fluorescent material and a garage or similar with no windows. Put the fluorescent material on the dashboard (you do call them that? The sort of mantelpiece thing inside of the windscreen) and have an accomplice (not needed, but experiments always seem to go better with accomplices/co-conspirators) shine the black light torch onto the fabric through the glass.

If the fabric fluoresces, then you're letting significant UV through the windscreen. You may wish to check side and back windows, too.