Risk Management > Radiation
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Radiation includes ultraviolet and visible light. Ultraviolet
radiation can cause disintegration and discolouration of the outer
layers of organic objects, and visible light can cause fading
(or, less often, darkening) of the outer layers of coloured components
in artifacts. Ultraviolet light is not necessary for humans to
view museum objects, and so should be avoided or eliminated in
museum display and storage areas. Some visible light is necessary
to allow visitors to see objects on display, but this must be
balanced against the stability of the colorants in the objects.
Fugitive colorants will change noticeably after just a few years
of display, even if they are displayed at low light levels (50
lux). Light damage will not cause complete physical destruction
of an artifact, but can affect the relevance of or the interest
in an object and can reduce its value considerably. Discolouration
caused by light damage cannot be repaired or reversed.
Costain, Charlie. Framework
for Preservation of Museum Collections, Canadian
Proper Lighting for Museum Safety (download as PDF format file),
Museum Management Program,
National Park Service, 2003.
Identified Risk: Harmful visible light and ultraviolet radiation
Identified needs and prioritized Goals
|____, first floor, Marble House.
|Light damage, wall fabric, west wall, ___, second floor, The
Light is a preservation risk factor to all collections almost regardless
of the nature of the materials. In its various natural and artificial
forms, light manifests its damaging effects in numerous ways. Most
commonly, it causes objects to fade and become embrittled. Often
too, it hastens invisible chemical deterioration reactions and promotes
related biological activities. While light is needed to appreciate
and display collections, it is important to be sensitive to the
principle that all objects have a total life expectancy for light
exposure. At no point can this process be reverse. Every time an
object is exposed to light, it is moving nearer to the closure of
its functional life-span. Therefore, in order to prolong the usefulness
of collections for generations to come, it is important to control:
- the quality of natural and artificial lighting
- the quantity of natural and artificial lighting
- the length of light exposure
Professional standards for museum light levels should be followed
and monitored closely as part of a collection care program. Site
managers need to be particularly aware of this risk factor and the
options available for mitigation. Because they are the responsible
staff consistently on site, the responsibility for monitoring and
mitigating the effects of natural light most realistically falls
to them. As part of an historic house maintenance plan, the site
caretakers needs to be trained in the management of light levels.
Further introductory information on the damaging effects of light
is available in the briefs on deterioration factors included in
the appendix. Specific recommended standards for light levels are
also explained. A summary follows below.
There are a number of ways that historic house museums mitigate
the effects of light on collections to extend their life expectancy.
There are three related light factors to consider.
(1) One is the elimination of ultraviolet radiation from all light
sources through the use of special films that absorb the harmful
ultraviolet radiation. This improves the quality of light and has
been undertaken at all the historic sites.
(2 The second is the reduction of light levels to meet recommended
museum standards of light strength or intensity. There are specific
levels to be met that are measured in standard units called foot-candles
(3) The third factor involves the duration or reduction in the
length of exposure of collections to light. A plan for collection
care needs to include ways to address these three factors that meet
the resources of the museum. Some can be implemented at no or very
little cost for immediate action, and some will require a moderate
financial outlay as resources become available.
The most swiftly damaging light force is exposure to daylight.
Not only is it too intense for museum collections, but also it is
composed of harmful, but invisible, ultraviolet radiation. As the
ultraviolet light causes our skin to burn with short exposure to
the outdoors, it similarly affects objects on display, especially
those of an organic nature. Because of the ephemeral nature of many
of the fine art materials and historical textiles and paper, exposure
to daylight through the windows and doorways in both exhibition
and storage areas is important to be controlled.
The most effective procedure in storage areas is to eliminate the
light all together. This must be done in the storage room, as daylight
is not needed under any circumstances. This can readily be accomplished
by blocking them. Painting the windows with an opaque paint, using
black out shades to cover them are viable options for eliminating
light in the storage area. Interior lighting should be control by
different switches for separate banks of lights within the room,
rather than from one switch.
If for aesthetic reasons the natural light in the historic house
museum cannot be eliminated, other approaches that minimize the
harmful effects of daylight must be implemented. This should be
viewed as a two part process. The first step is to eliminate the
ultraviolet radiation. The second is to reduce the intensity and
duration of the remaining light levels. The most effective and efficient
method to address the first step, is to apply an ultraviolet absorbing
film directly to the windows by a professional glass treatment company.
A less costly method but more labor intensive for staff is to purchase
the film in a polyester sheet form from which shades or interior
screens are made to cover the windows. The third choice
is to purchase UV filtering Plexiglas to cut to shape. The PSNC
has addressed the initial step by applying UV filtration films to
all windows in the historic houses.
Guidelines for Light and Lighting in Historic Buildings that House
Collections, APT Museums in Historic Buildings Committee, Association
for Preservation Technology, International.
and Ultraviolet Radiation, Volume three:Damage and Decay, reCollections:
Caring for Collections Across Australia, Heritage
Collections Council, Australia.