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Re: filmscanners: Re: looking at the Sun

>From a prctical point of view, I seriously doubt that glass absorbs a heck
of lot of UV, certainly not over a long term.

Case in point:  my house is on a hill, facing southeast.  The roof overhangs
3 feet on all sides and the windows facing over the valley are all floor to
ceiling glass (they're standard sliding glass door sections, 6'8" high by 4'
wide -- or about 3 meters high and about 1 1/3 meters wide) fixed in place.
The interior roof (all recycled 90 year old redwood & fir) slants upwards
from there to the peak of the house at about 15 feet.

These glass panels are all double paned (the inner one made of tempered
glass as in autos) with a dead air space between for insulation purposes.
Our carpeting is royal blue and was first installed in 1975.  We replaced it
in 1995 but the closer you got to the windows, the lighter colored it became
until the last few feet of carpet (a meter maybe) were bleached absolutely
white by the UV in the sunlight, which had to pass through two sheets of
glass to do the bleaching.

These windows have now been replaced by sealed glass panels of the same
contruction, including the dead air, excpt that the inner tempered glass
panel now consists of two tempered glass panels with a special absolutely
clear anti-UV filtering layer between them.

Also, all framed photos, art prints, etc. in the areas where these windows
are use special anti-UV glass which also has a UV filter layer on its back
side.  None of the images are within range of direct sunlight nor are any of
the books on the bookshelves.  Nonetheless, the spine portion of all of
those books with so much of a trace of red in them are bleached out.

So I doubt the the ability of glass to absorb UV in any serious way!

Hart Corbett

>From: "Alan  Tyson" <AlanTyson@bknowl.freeserve.co.uk>
>To: <filmscanners@halftone.co.uk>
>Subject: Re: filmscanners: Re: looking at the Sun
>Date: Sun, Feb 4, 2001, 11:52 AM

> Most glasses absorb UV much more strongly than IR. Most of
> the materials used for sun viewing and photography (eclipse
> goggles) have a  (log10) density of 5-8 for UV and visible,
> and less than 5 for IR.

> Alan T


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