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Providing collection care, preservation and conservation treatment services to collectors and collecting institutions. |
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Collection Care > Environment
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LightDifferent types of materials are adversely affected at varying rates by light, UV and IR radiation. Degradation occurs when a material absorbs the radiation. This occurs if the molecules of the material are susceptible to damage by the wavelength of the light, UV or IR energy. Organic materials are most susceptible to this form of degradation. For example, excessive light, UV and IR exposure can cause fading of dyes and color shifts in textiles, leather, wood and paper; weakening and embrittlement of some organic materials; and yellowing and cross-linking of varnishes. Generally, the shorter the wavelength, the more damaging the light to the physical stability of an organic material. At a given level of illumination, ultraviolet light (measured in microwatts of UV radiation per lumen of visible light) is the most damaging of all. Light from an overcast sky through glass, which contains high levels of UV radiation, is five times as damaging as a tungsten light at the same level of visible illumination. Traditionally, conservators have recommended that if a museum light source emits more than 75 microwatts per lumen (mW/l) of ultraviolet radiation it requires a UV absorbing filter. In the past year, new recommendations by staff at the Canadian Conservation Institute suggest eliminating UV radiation completely, aiming for under 10 mW/l through the use of window films and UV absorbing light covers. Recent experiments have shown that ultraviolet radiation weakens physical structures, such as causing paper to embrittle, but visible light is more likely to fade dyes and pigments. Visible light levels also should be kept at a minimum. Usually 50 lux (or 5 foot-candles) is recommended for watercolors and textiles; 150 lux (or 15 foot-candles) is recommended for oil paintings, wood, and leather. Most unvarnished metals, ceramics and glass do not require light controls, but staff should judge each piece based on added decoration and associated parts. Not only must the wavelength and intensity be considered, but also the duration of exposure. The total time that sensitive materials are exposed to light directly relates to the amount of damage incurred. Several months of exposure at very low levels can have the same effect as a few days exposure in bright sunlight. Damage from light is always cumulative; its effect on artifacts cannot be reversed by subsequent storage in darkness. In general, keep your light levels as low as possible. Visible light should be under 5 fc (50 lux) for light sensitive materials such as many textile dyes and watercolors. Less light sensitive material should be displayed at levels under 15 fc (150 lux). If your audience is older, you may want to raise the light levels. When light levels are raised, they must be balanced by decreasing the exposure time. Limiting exposure time techniques include shortening the exhibit time, using visitor sensors to trigger lights on only when the material is viewed, and limiting exhibit times to a few hours on certain days.
Furniture Care & Handling - Light
Museum Lighting Protocol, NCPTT
Environmental Control: Services and Supplies
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Environment
|--Light--|--Relative Humidity & Temperature--|--Pollutants--|
Collection Care
|--General--|--Environment--|--Numbering--|--Storing--|--Exhibiting--|--Handling--|--Cleaning--|
|--Care by Type--|--Pest Control--|--Security--|--Long Range Planning--|--Emergency Preparedness--|
