Liam Lawless (lawless@vignette.freeserve.co.uk)
Sat, 30 Jan 1999 23:12:43 +0000
Hi Walt,
Felt someone should acknowledge your contribution on UV. We're all good at
giving advice to others but probably few of us, including myself, take the
hazards of what we do as seriously as we should, and need an occasional
reminder. Thanks.
Liam
-----Original Message-----
From: Walt Goettman <wgoettman@mm.wyeth.com>
To: alt-photo-process-l@usask.ca <alt-photo-process-l@usask.ca>
Date: 29 January 1999 13:30
Subject: UV and eye safety
>>
>> UVA has one nasty effect on eyes, known as "nuclear cataracts". This is a
permanent "tanning" of
>> the lens of the eye. "Nuclear" refers to this occuring mainly in the
center of the lens of the eye. You
>> need lots of heavy exposure to get this. Nuclear cataracts occur mainly
among people who work
>> outdoors.
>> Although incandescent blacklights emit wavelengths that cause nuclear
cataracts, they are largely
>> safe since you typically get less UV exposure from these than from
sunlight. Even considering the
>> fact that your pupils are wider under blacklight than under sunlight,
there is so much less UV that it
>> is safe to stare into the bulb from a few feet away for large amounts of
time. (No warranty, so I
>> don't recommend this.)
>> Fluorescent blacklights are worse, but are usually comparable to sunlight
when you are a couple
>> feet away. Although I have yet to hear of eye damage blamed on reasonable
use of blacklights,
>> those who are around them a lot may want UV blocking eyewear.
>>
>> Persons who have had cataract surgery need extra protection, since the
lens of the eye largely
>> absorbs UV. The retina does not like strong exposure to UV.
>>
>> It should be noted that UVA-related eye damage involves a process with at
least two steps. The first
>> step (excitation of tryptophan or related molecules) normally reverses
itself. Damage requires
>> excited molecules to receive additional UV before they de-excite. This
means that UVA eye damage
>> is not linearly proportional to the intensity of exposure, although it
may be proportional to the
>> duration of exposure of a given intensity.
>>
>> I have yet to see data indicating clearly what is and is not safe.
However, nuclear cataracts are most
>> common in people who work outdoors in sunny areas. In case of doubt, use
UV blocking eyewear.
>> Cheaper amber and yellow sunglasses do actually work - I have tested
them. Sunglass lenses made
>> of real glass and green in color attenuate UV a fair amount. Clear, blue,
purple, or pink glasses may
>> not work, even if they are claimed to work. I saw one pair of clear
glasses with a sticker claiming
>> "100 percent UV blocking" which let through more UV than window glass
did.
>>
>> UVB is worse on eyes than UVA, and can burn the cornea and the
conjunctiva. UVC is especially
>> burning to the conjunctiva. Please beware that symptoms are delayed
considerably from exposure.
>> Symptoms typically begin a few minutes after exposure and gradually
increase for at least a half
>> hour, often an hour to a few hours after exposure. If you have been
exposed and any symptoms
>> begin, promptly seek emergency medical care to minimize damage.
>>
>> SOME OTHER HAZARDS
>> ------------------
>>
>> (Not complete)
>>
>> Prolonged, heavy UV exposure causes some plastics to turn a brownish
yellow color. A few of
>> these plastics are also affected (to a lesser extent) by shorter visible
violet wavelengths such as
>> mercury's 404.7 nM deep violet line.
>>
>> SOME WAYS TO REDUCE UV HAZARDS
>> ------------------------------
>>
>> UVB and UVC, as well as the shortest UVA wavelengths, do not go through
ordinary glass. Even
>> Pyrex and other more ordinary forms of heat-resistant glass can be used
as shields to block UVB
>> and UVC.
>>
>> Another option is to contain all light from the suspect source. For
example, EPROM erasers often
>> have an interlock switch to prevent operation with the lamp exposed.
>>
>> In the event you need something transparant to visible light (and most
infrared) but which blocks all
>> UVC, UVB, and well over 95 percent of UVA, use a GAM ("Great American
Market") number
>> 1510 (UV shield) filter gel. This is available from some theatrical
supply shops. If very severe
>> exposure is anticipated, the filter gel should be preceded by glass.
>>
>
>Check out http://www.misty.com/~don/light.html for this and lots of
>other light source info.
>
>Walt
>
This archive was generated by hypermail 2.0b3 on Sat Nov 06 1999 - 10:06:45