Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!bu-cs!dartvax!eleazar.dartmouth.edu!earleh
From: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Newsgroups: comp.sys.mac
Subject: Re: Ott Computer Safety Light
Keywords: Magntic Fields, Blood, Eye Strain, Radiation
Message-ID: <15525@dartvax.Dartmouth.EDU>
Date: 11 Sep 89 23:27:52 GMT
References: <15388@dartvax.Dartmouth.EDU> <2979@ur-cc.UUCP> <1589@draken.nada.kth.se> <11557@boulder.Colorado.EDU>
Sender: news@dartvax.Dartmouth.EDU
Reply-To: earleh@eleazar.dartmouth.edu (Earle R. Horton)
Organization: Thayer School of Engineering
Lines: 33

In article <11557@boulder.Colorado.EDU> pratt@boulder.Colorado.EDU
	(Jonathan Pratt) writes:
>In article <1589@draken.nada.kth.se> h+@nada.kth.se (Jon W{tte) writes:
>>
>>You ARE aware that recent research indicates that it's the UV from CRTs
>>that hurt the eyes the most (can cause blindness, and a disease that I
>
>I was under the impression that most glass is opaque to UV.  Is there any
>reason the glass used in CRTs wouldn't have this property?

No, but the situation is more complicated than that.  It is true that
glass has an absorption band in the ultraviolet, and that therefore
glass will stop most ultraviolet light.  There are many types of glass,
however, and each type has its characteristic resonant frequency and
bandwidth for absorption.  What this means is that for each given glass
type, some UV will get through, and the frequencies passed will depend
on the types and amounts of impurities in the glass.  There is really
no such thing as perfectly opaque.

Furthermore, since the absorption band is in the UV, it follows that if
you make the frequency high enough, light will start to get through
again.  As a rule of thumb, the higher the frequency, the more damage to
living tissue.

There are tables of optical properties of glass, but without consulting
these I am confident that for some combinations of glass type and
CRT electronics there is some leakage of UV and some risk.  If you want
to be sure, then look up the actual research papers.

My eyes hurt like heck now, but I am quite sure that it is just my
contacts drying out.

Earle R. Horton