NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/med/23251

Internet Message Format | 1992-12-30 | 3.4 KB

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From: [e-mail] (Oren Haber-Schaim)
Newsgroups: sci.med
Subject: Re: Health hazard in halogen lights?
Message-ID: <[e-mail]>
Date: 31 Dec 92 03:00:17 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Lines: 64
Nntp-Posting-Host: husc9.harvard.edu

[e-mail] (Anmar Caves) writes:

 >This is somewhat incorrect.  Without a UV filter, the UVA and UVB
 >output of a 50 watt QH (quartz-halogen) desk lamp at 1 foot
 >can be greater than noontime sun on the earths surface.  This may not
 >be so much of a problem for your skin, but your eyes will be affected.
 >UV tends to reduce the opacity of the cornea over time, and much of
 >the damage is not reversible.  All of this is moot, however, if a
 >simple glass lens is used with the lamp, as the glass will filter much
 >of the UV.
 >--
 >Anmar Mirza   # Chief of Tranquility  #My Opinions! NotIU's!#Purveyor of
 >EMT-D         # Base, Lawrence Co. IN # Legalize Explosives!#nontraditional
 >N9ISY (tech)  # Somewhere out on the  # Politicians prefer  #family values
 >Networks Tech.# Mirza Ranch.C'mon over# unarmed peasants.   #Space For Rent


One might charitably call the above "homeopathy applied to optics".

Let us do a simple order-of-magnitude calculation:

A 50 watt halogen lamp was hypothesized.
Using the surface area of a 1 ft. sphere (due to 1 ft distance hypothesized
by the same poster) gives less than 1/10 of that per square foot, which
comes to 5 watts per square foot.

However, the wattage specified by lamps is the
electrical input.   Tungsten-halogen lamps emit about 10% of their
input power as light, which brings us to about 0.5 watt per square foot.

Now, the following fact may be surprising, but noon solar
insolation (sic)  can be about 100 watts per square foot.
Unlike an incandescent lamp, the sun's spectrum is centered in
the visible wavelength range, rather than in the infra-red, so it is
far more efficient as light.  Still, give it a penalty of 70%, = 30%
efficiency, which gives us 30 watts per square foot of
"light" from the sun vs. 0.5 watt from the lamp, a ratio of
60 times more light from the sun than from the much-feared lamp.

Even this ratio of 60 is an understatement because the solar
spectrum is so much more UV rich, due to its being centered
in the visible rather than in the infra-red, which is the opposite
end of the spectrum.

None of this should surprise anyone when one considers how many
people have gotten suntans or sunburns from household
(or other) tungsten-halogen lamps!


Regarding "UV reducing the opacity of the cornea", if one knew what
"opacity" means, its not such a big word, then one would know that
 UV tends to increase opacities (of whatever), not cause reduction.

Finally, paraphrasing, "If a simple glass lens is used then there is no
problem from UV":  this may be the only correct statement in the post,
but even here, _all_ households tungsten-halogen lamps that I am aware
of (other than those that point at ceilings, with bulbs hidden from view)
have a glass cover of one sort or another (aside from UV, the
bulb is under very high pressure so it is a spatter shield), so
the "If" qualification should be unnecessary.

Oren Haber-Schaim                     ([e-mail])