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Limiting Light Damage
Why should you care about light damage?
Why does the light source matter?
Which things are most sensitive to light? (and associated display recommendations)
Other risks from display (and mitigation strategies)
Limiting light display in non-display situations
The information on this page concentrates on cultural heritage materials typically found in library and archive collections (books, documents, photographs, and art on paper) and is intended for professionals working in institutions that collect, preserve, and present these materials to the public. Please see the additional resources, listed below, for information on limiting light damage to other cultural heritage materials such as paintings, textiles, natural history collections, etc. For advice on how to care for personal collections and family photographs, please see our Collections Care section, Guidance for Various Format Types.
Why should you care about light damage?
Light can cause permanent and irreversible damage to the chemical composition, physical structure, and appearance of collection items. Light damage is cumulative and follows the reciprocity principle. In other words, dim light over a long period of time is just as damaging as bright light over a short period of time.
Common examples of damage from light exposure include fading, yellowing, darkening, bleaching, embrittlement, and color change. These types of light-induced damage can affect the item’s aesthetic appearance as well as its informational value, and diminish its ability to be safely accessed. In most cases, conservation treatment cannot reverse light damage. Even in instances where some visible manifestations of light damage can be lessened, the chemical and physical damage to the material cannot be undone.
Why does the light source matter?
Light sources vary widely and include daylight, tungsten incandescent, halogen, fluorescent, metal halide, and LED among others. Each source has different characteristics and should be evaluated independently based on need. However, general guidelines recommend reduction of ultraviolet (UV) and infrared (IR) radiation. UV and IR radiation fuel chemical reactions that lead to deterioration. Additionally, IR radiation produces heat, which in turn can affect relative humidity, and cause damage to an item as a result of dimensional change (expansion/contraction) due to absorption and desorption of moisture. For this reason, all light sources used for display should ideally produce only visible light, with UV or IR eliminated. If UV cannot be removed from the light source, then collection items can be protected behind UV-absorbing glazing materials. If a light source produces heat, then it should be located outside of the display case with sufficient air flow to reduce heat buildup. Generally, sunlight is avoided for display of light-sensitive items as it is too intense, contains high levels of UV, and is difficult to control. Visible light, even with all UV and IR removed, is still damaging to collections and should be controlled and monitored appropriately.
Which things are most sensitive to light? (and associated display recommendations)
It is difficult to know precisely the light sensitivity of an individual item as it depends on the item’s unique manufacture and history. Microfade testing (an analytical technique that exposes a minute area of a collection material to a short burst of intense light while simultaneously measuring the color change to that area) can provide data specific to an individual item. However, when item-specific data is unavailable, general display recommendations can be used to guide decision-making for large classes of materials. It should be noted that accurate identification of the material is a crucial first step in decision-making and the nuances of the individual item should always be considered when using general guidelines.
The International Organization for Standardization (ISO) developed the Blue Wool Standard, ISO 105-A01, to characterize the lightfastness of materials. The standard consists of eight wool cloths, each colored with a different blue dye of a known lightfastness. BW1 is the most fugitive and BW8 the most stable. Each BW requires about twice as much light exposure as the preceding in order to fade to the same degree. In other words, BW1 is about twice as light sensitive as BW2. Most library and archive materials fall within the high light sensitivity categories of BW1-3.
Visible light levels can be measured with a light meter and intensity levels reported in units of lux or foot- candles. Both the intensity and the duration of the light exposure are critical to document. In order to ensure long-term preservation of an item, keep accurate records of light exposure over time and limit light exposure as these guidelines suggest. However, in some instances the importance of access may lead to decisions that diverge from preservation guidelines. For example, it may be crucial for an item to be included in a pivotal exhibition or it may be necessary to display an item under increased light levels in order for the item to be appreciated by viewers with reduced visual acuity. In those instances accurate record keeping of the item’s cumulative light exposure and critical evaluation of long-term goals for the object’s serviceable lifetime is vital to the development of informed compromise.
Extremely light sensitive -- Do not display; strictly limit use; invest in a reproduction
- certain kinds of early and experimental photographs including stabilized salted paper prints (photogenic drawings), autochromes, stabilized silver gelatin prints, and some color dye processes
- color transparencies/slides and motion picture films
- degraded plastics
Very light sensitive -- Avoid display and limit use whenever possible; strictly control light levels (max 3 foot-candles and only when being viewed) and duration (max 3-5 months) of display followed by a minimum of 3 years of dark storage between display cycles; monitor object closely while on display for any sign of change using photographic documentation and/or spectrophotometric readings as basis for comparison
- poor quality papers with high lignin content (e.g., newsprint, many books printed in the U.S. between 1860-1990)
- colored papers
- drawings and documents with ball point or felt tip pen ink, iron gall ink, purple manuscript ink, pastels, colored pencil, or colored wax
- watercolor paintings
- any print with non-earth based colored pigments or dyes present
- architectural plans and photo reproductions including blueprints/cyanotypes, diazotypes, van dykes, brownlines, photostats, and pellet prints
- hand-colored photographs
- all color photographic processes
- all digital photographic prints including inkjet prints
- all silver gelatin prints on resin-coated (RC) supports
- any poorly processed or highly deteriorated photographic prints
- cased photographic objects such as daguerreotypes, ambrotypes, and tintypes where the dyed leather and textile elements of the case are exposed
- dyed organic materials (e.g., dyed leather, textiles)
- plastics
Moderately light sensitive -- Strictly control light levels (max 5-10 foot-candles) and duration (max 6-9 months) of display followed by a minimum of 2 years of dark storage between display cycles; monitor object closely while on display for any sign of change using photographic documentation and/or spectrophotometric readings as basis for comparison
- high quality paper
- parchment
- undyed leather
- any print with only carbon or earth-based pigments present (no dyes)
- metal point drawings
- most silver-based photographic processes including salted paper, albumen, collodion, and silver-gelatin prints that are in good condition with no hand-coloring or tinted binder present
- platinum and palladium prints
- daguerreotypes, ambrotypes, and tintypes displayed without a historic case (no dyed leather or textile elements present)
Limiting light damage in non-display situations
It is important to reiterate that light damage is cumulative and therefore light exposure from non-display situations such as storage and research access should also be considered and minimized when possible. UV radiation can be removed or blocked from light sources and overall light exposure can be minimized in storage areas and reading rooms. Collection items can be placed in light-tight storage boxes and lights can be turned off when storage spaces are not occupied. Light-sensitive items should never be left out and exposed to light when not being used.
Other risks from display (and mitigation strategies)
Light exposure is not the only cause for deterioration during display. Other risk factors to consider include:
- temperature
- relative humidity
- pollutants
- security
To prevent theft and vandalism, displayed items should be placed inside a secure exhibition case or framed and securely attached to the wall. Elevated temperature, relative humidity and pollutant presence can cause damage to an item independently but it can also increase the rate of deterioration caused by light exposure. Monitor the temperature and relative humidity inside the display case and the exhibition space to ensure the environment stays within recommended parameters (determined by the material type of objects displayed). All construction and trimming materials used for and in the display case should be chemically inert and pass the Oddy test or photographic activity test (PAT), ISO 18916.
Additional resources
Agent of Deterioration: Light, Ultraviolet and Infrared. Stefan Michalski. Government of Canada, 2018.
Guidelines for Exhibition Light Levels for Photographs. Sarah Wagner, Connie McCabe, and Barbara Lemmen, Topics in Photographic Preservation volume 9, Washington DC: PMG-AIC, 2001.
Light (Philadelphia Museum of Art)
Microfading Tester: Light Sensitivity Assessment and Role in Lighting Policy. Vincent Laudato Beltran, Christel Pesme, Sarah K. Freeman, and Mark Benson, Los Angeles, CA: The Getty Conservation Institute, 2021.
Museum Lighting: A Guide for Conservators and Curators. David Saunders, Los Angeles, CA: The Getty Conservation Institute, 2020.
Notes. Canadian Conservation Institute (CCI), Government of Canada.
Protection from Light Damage (Northeast Document Conservation Center)
The Manual of Museum Exhibitions 3rd edition. Maria Piacente, Washington DC, Rowman & Littlefield publishers, 2022.