Jamie,
All T-12 bulbs give off UV light due to the technology of fluorescence, to
the best of my knowledge. Various manufacturers (such as Verilux) offer
T-12 bulbs with UV-absorbers incorporated into the bulb. Generally, this is
a coating on the outside of the bulb, so it acts essentially like a
VU-filtering sleeve. The UV-filtering bulbs are significantly more
expensive than regular bulbs without the filtering, but less expensive than
having your collections deteriorate. They also have a lower CRI (color
rendering index or how close the bulb is to true daylight color [a subject
that in itself is very complex]), which makes sense, since the filters,
whether coatings or tubes, filter out a bit of the violet light as well as
the ultraviolet, making them appear yellow. If you look at a spectral curve
of light emission, as well as filtering, it doesn't start and stop precisely
at a particular wavelength. It is more of a bell curve, but a bit more
steep. A filter can be made that does not have a yellow color, but then it
will let through a bit of the UV, thus allowing some damage.
Each manufacturer has different specs for their products. You will need to
request copies of the spectral curves to see how they perform. This
includes manufacturers of UV-filtering sleeves as well. I don't believe
that anyone has tested all of the different UV-filtering bulbs and sleeve
combinations to see how they compare. If they have, I'd love to see the
results! If you already have the UV-filtering sleeves and they are still
working properly, it is probably less expensive to use a good CRI bulb with
your existing sleeves. It may even be less expensive to buy new sleeves
with new bulbs, depending upon the cost differences with UV-coated bulbs.
Measuring UV output requires rather expensive equipment, so if you are in
doubt about the effectiveness of your sleeves, it would be best to get new
ones. Whether you get filtering bulbs or sleeves, be sure to ask the
manufacturer if they have any data on long-term effectiveness of the
UV-filtering. Then choose the best alternative for you.
However, don't forget the visible light - it, too, will cause damage. So,
light levels in the cases are important even if the bulbs filter UV. Output
on T-12 bulbs can not be regulated (dimmed), so the only way to control
light levels is with the number of bulbs and the distance from the objects.
Only place light-insensitive objects near the bubs, and locate
light-sensitive ones further away from the bulbs. An inexpensive light
meter will tell you what's an appropriate distance.
Marc Williams
American Conservation Consortium, Ltd.
4 Rockville Road
Broad Brook, CT 06016
www.conservator.com
860-386-6058
*Collections Preservation Consultation
*Conservation Assessments & Surveys
*Low-Tech Environmental Control
*Moisture Management Solutions
*Collections in Historic Structures
*Conservation Treatment of:
Furniture
Painted Wood
Horse-Drawn Vehicles
Architectural Interiors
Marc A. Williams, President
MS in Art Conservation, Winterthur Museum Program
Former Chief Wooden Object Conservator, Smithsonian Institution
Fellow, American Institute for Conservation (AIC)
----- Original Message -----
From: "Jamie Smith" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, October 13, 2006 12:27 PM
Subject: [MUSEUM-L] light bulbs with less UV
> Hi all,
> We are trying to find better light bulbs for our exhibit cases. Has anyone
> come across light bulbs that put out less UV than using florescent bulbs
> with UV filters?
> We are trying to find something that might fit our existing light fixtures
> which are four feet and use T-12 bulbs. Any leads on vendors that might
have
> something that would work for us would be appreciated.
>
> Many Thanks,
> Jamie Smith
> FASNY Museum of Firefighting
>
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