Re: IR UV and other nasty stuff!

[P3D Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

Dr. George A. Themelis writes

>This raises more questions:  How much UV is going through the glass lenses?
>Is it true that a simple piece of glass blocks UV?  If yes, should an extra
>piece of glass before the slide protect the slide from fading?  Are halogen
>quartz bulbs more damaging to slides than regular glass tungsten bulbs?

>I suspect that the answer is not that simple. -- George

Actually it depends if it is the short or longer UV wavelengths we are
talking about. The longer ones of course are closer to the visible and
the shorter ones progressively farther out. Glass will protect to a degree
against the more damaging shorter UV rays but not to the less but still
damaging (and fading) longer UV rays. The ironic thing is that Halogen
lamps use quartz in their glass envelope which allows alot of the shorter
UV rays to transmit very well! Thats why they call them QTH or quartz-
tungsten-halogen. Of course the tungsten and halolgen decribe the other
elements of the lamp. The other lenses if made of glass will help protect
against the UV but I think plastic, maybe some kind of plexi glass would
help to absorb the damaging UV. Don't know if it could take the heat thou,
unless it was strategically located before the film.

Gabriel



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