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Subject: Window films

Window films

From: Lisa Mibach <heritage1>
Date: Saturday, November 15, 2003
Gregg Grunow <virginiana [at] nngov__com> writes

>Our special collection room has very large windows, which look nice,
>but are undoubtedly letting in too much sunlight.  I wish to submit
>a proposal to have plastic window film applied. ...

Seconding and furthering  Ellen Pearlstein's point about the
limitations of uv filtering window films, in addition to the
requirement to filter to 400 nm, there are two other points related
to human behavior which might be taken into consideration:

1.  My (outdated) memory of specs is that none of the films reduced
more than 90% of visible light. This means that in a display space
with windows, one still does not reduce the ambient light level to
one safe for the display of delicate items.

However, those responsible for deciding where exhibits are located
will insist on putting them in the areas with film, as these are now
"treated" and therefore safe. Attempts to further explain the
subtleties of lux levels are often received as another example of
picky uncooperative conservators.

Example: With the Director's support, we added neutral gray tinted
film to the foyer spaces of our museum, where the Director had
decided to display temporary exhibits (against our recommendations).
We also added controllable tungsten lighting and blackout drapes.
Light sensitive exhibits were set up with both the blackout drapes
and appropriate light settings, but because the area was now "safe"
because of the dark film, both the Director and guards obligingly
opened the drapes when visitors complained about the low light
levels (made more obvious by the abrupt, non-transitioned change
from the exterior). After a cordial meeting of explanation with the
Director, he had locks placed on the drape controls...and then
turned up the levels on the tungsten lights!

This was not just the idiosyncrasy of that particular director, but
was found consistently in historic houses which had had film
installed. I believe this misunderstanding of the limitations of
window film may be related to the mental focus of people in
different kinds of jobs.

2) In the first example above, there were two additional unintended
consequences:

    a.  visitors to the museum turned away before entering and then
        complained about changed hours of operation, because it
        appeared that the absence of visible lights from outside
        indicated that the museum was closed.

    b.  the guards stationed in the foyer area became noticeably
        grouchier-one finally explained that they could no longer
        "feel" the changes in light that indicated changes in
        weather or time of day, even though they were standing near
        the windows. (This is particularly true if the film is a
        color other than neutral grey.) Our mammalogist suggested
        that this might be related to an ancient physiological
        warning to take cover at dusk when predators emerge, and may
        help to explain why humans are more comfortable with low
        light levels of tungsten (warm, cosy) than low levels of
        natural light.

A further point related to 2a is the change in exterior appearance
of historic buildings fitted with dark film.

Since the film was really only dealing with uv, and not the amount
of visible light, I have since recommended the use of non-tinted
film with the requisite uv rating. This retained the appropriate
period appearance of the exterior, and we have since had no further
problems with compliance in the use of historically appropriate
drapes in light-sensitive areas.

Lisa Mibach


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                  Conservation DistList Instance 17:43
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Received on Saturday, 15 November, 2003

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