Risk Management > Radiation (Light)

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Existing Conditions



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 Heritage, 1994.




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 Elms.

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:

  1. the quality of natural and artificial lighting
  2. the quantity of natural and artificial lighting
  3. 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 or lux.

(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.

APT/AIC Guidelines for Light and Lighting in Historic Buildings that House Collections, APT Museums in Historic Buildings Committee, Association for Preservation Technology, International.

Light and Ultraviolet Radiation, Volume three:Damage and Decay, reCollections: Caring for Collections Across Australia, Heritage Collections Council, Australia.

   © 2002-03 Philip C. Marshall and Preservation Society of Newport County