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From: email@example.com (Don Klipstein)
Subject: Re: homemade uv exosure unit
Date: Thu, 26 Dec 2002 23:33:43 +0000 (UTC)
Organization: MGT Consulting
NNTP-Posting-Date: Thu, 26 Dec 2002 23:33:43 +0000 (UTC)
User-Agent: slrn/0.9.6.3 (SunOS)
In article , Da Man wrote:
>The scary part is how much UV people are staring into when they use overhead
>projectors :-( Makes me want to wear sunglasses to block the UV when using
>them. At least it's mostly long wave UV. Makes me wonder about all the UV
>all the halogen bulbs give off commonly in use, and if they cause any long
>term exposure problems like cateracts.
Halogen lamps have more UV than an equivalent amount of incandescent
light, although usually not a whole lot more - except projector lamps and
photoflood lamps produce substantially more - but still only a fraction of
the amount found in an equivalent amount of sunlight or daylight.
In an overhead projector, the light has to pass through a plastic
Fresnel lens and a glass surface that block all of the UVC and UVB and all
of the suntanning portion of UVA coming from the halogen bulb. The UV
gets to be very much a non-problem compared to sunlight and daylight.
Photographic and projector halogen bare bulbs can be a bit of a problem
however. They usually come in packages with a warning to operate them
only in equipment designed to use such bulbs (and which usually have glass
lenses or other things that block the nastier shorter and medium
wavelengths of UV). Another reason to operate quartz halogen bulbs only
when enclosed as intended is that every few blue moons one explodes, even
if you keep them free of salts, alkalis, ash, etc. which can leach into
the red-hot quartz bulb and cause weak spots in it.
- Don Klipstein (firstname.lastname@example.org)
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