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Re: HF Welding helmuts?

To: Don Malling <dmallin@attglobal.net>
Subject: Re: HF Welding helmuts?
From: David Scheidt <dmschei@attglobal.net>
Date: Sat, 8 Nov 2003 23:00:30 -0500
>Well, that is interesting.
>
>They warn about getting "flashed" if the helmet turns off the 
>battery when you're not using it, and the helmet doesn't auto 
>darken. They also suggest auto darkening of .0004. More doesn't 
>matter.
>
>Sounds like your eyes will "hurt" from the brightness but not be 
>damaged because the lens filters the IR and UV regardless of whether 
>it's darkened or not.
>
>Sounds kind'a funny. Why do your eyes hurt if they're not being hurt 
>by the IR and UV. I suppose just the brightness -- eye muscle strain 
>trying to close down the pupils to reduce the brightness -- still 
>sounds kind'a funny. I wonder. I thought you shouldn't look directly 
>into the sun because of the brightness, not because of the IR or UV. 
>Maybe IR and UV are not reflected. They are absorbed by the things 
>around us, so your eyes don't get the sun's UV or IR unless you look 
>directly at it? Maybe....

There's a difference between strain from brightness, and (permanent!) 
damage from UV.  My eyeglasses have a coating on them that absorbs UV 
light, but my eyes still hurt if I'm out in bright sun for a long 
time (which is why I've got a pair of clip on shades).  Some cheap 
sun glasses don't block UV light (though the regulations on this have 
changed, so there may not be any like this anymore), but do block a 
bunch of visible light.  That means your pupils are open wider, and 
you suffer more UV damage wearing them than you would without them.

UV light is reflected off many things.  Reflected UV light is one of 
the reasons skiers tend to get sunburned.

David, who loves his cheapy solar powered autodarkening helmet.





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