Quantifying light exposure

At the Canadian Centre for Architecture we are reconsidering the
duration of our in-house exhibitions and the length and frequency of
venues for our travelling exhibitions.  Since our collections
consist primarily of works of art on paper, I referred to Karen
Colby's excellent article, "A Suggested Exhibition Policy for Works
of Art on Paper" (Journal of the International Institute for
Conservation - Canadian Group, Vol. 17, 1992) in which Karen
suggests a "multicategory system of classification for works of art
on paper" based on the various light sensitivities of objects in
these categories.  Exposure limits can be set as a factor of the
number of megaluxhours to which an object in any one sensitivity
category can be exposed before first noticeable fade occurs.

To work out a policy for our collections, I tried to make some quick
calculations of the number of lux-hours per week to which objects
are exposed during exhibitions at the CCA and when they are on the
road.  In looking at our in-house venues, I found that I could not
rely on our museum's hours of opening as the basis for the
calculations.  To our summer hours--6 days a week at 7 hours per day
plus one evening--I had to add the additional hours that the
galleries are lighted for regular floor maintenance, photography
sessions, student tours, social events, etc.  I was surprised at the
total.  One more hour here and 2 more hours there added up to quite
a significant number over the course of a 3 month show.  I wondered
if, while travelling, our shows were also being exposed to light for
many more hours than I'd imagined.  And I wondered if, in other
institutions, the persons responsible for collections
preservation--be they conservators, registrars or other--really know
exactly how long objects are being lit there every day, or, like me,
are they basing exhibition and loan recommendations on the sometimes
false assumption that the galleries will be lit around 40 hours per
week?

I would like to hear from anyone who has comments to make on this
issue.  Do most of us know how long our galleries are really lit
every week?  Do we have any influence over the forces (eg. the
increasing importance of public programming) which may demand
extended gallery hours?  Should we require information on the
duration of gallery lighting from borrowing institutions whenever we
consider a loan request?  Should Standard Facilities Reports include
questions on the duration of gallery lighting in addition to the
existing questions about lux levels and UV?  (Or would everyone just
give the expected response, "42 hours a week", leaving us as
uninformed as before?)

Karen Potje
Head, Conservation/Preservation
Canadian Centre for Architecture
1920 Baile Street
Montreal, Quebec H3H 2S6
514-939-7000 x 1236
Fax: 514-939-7020

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                  Conservation DistList Instance 11:94
                   Distributed: Tuesday, May 19, 1998
                       Message Id: cdl-11-94-014
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