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Light Damage to Cultural Heritage
Objects within the care of a repository are often vulnerable to damage caused by light. Preventative conservation is key to minimizing any light damage to cultural heritage during their storage, display, transport, and treatment. Preventative conservation against light is in part limiting the exposure to light over the object's lifetime. It is the accumulation of light exposure over time that is the most damaging to objects. Conservators, collectors, or other institutional staff, typically use handheld light meters that can measure just how much light an object is being exposed to. It is with these types of tools that individuals can establish procedures or guidelines for limiting an object's exposure.

Measuring Light Exposure
Light exposure is measured in units of energy. These units are "footcandles" or "Lux". Footcandles are the amount of light that is produced by one candela from the distance of one foot, and ten lux equal one footcandle. The amount of light an object is being exposed to can be measured by a light meter.

Preventative Measures
While not possible to completely avoid light damage, repositories can follow traditional recommendations, Light Exposure Standards, ISO Blue Wool standards, Canadian Conservation Institute's light-damage slide rule, or establish their own procedures or guidelines to follow in order to minimize as much potential damage as possible.

Recommended Light Levels
The traditional recommended light levels for sensitive materials such as textiles, botanical and zoological specimens, pigmented objects, works on paper, and organic materials such as feather, furs, and skin is no more than 50 lux or 5 fc. Moderately sensitive objects like oil paintings can be exposed to 15-20 footcandles or 150-200 lux Other materials may be more resilient against light damage. for example, stone, ceramics, metals and glass can be exposed to no more than 300 lux or 30 footcandles.

Meeting the Standards
Repositories can work to achieve these standards by avoiding tungsten, halogen, and even fluorescent light. These types of lights also can create a lot of heat which increases chemical deterioration New sources of light such as light-emitting diodes (LEDs) may be used because they are not only energy efficient, but they emit little to no ultraviolet or infrared radiation

Recommended Measures

 * Regular use of blinds, shades, curtains, and shutters.
 * Filters on existing windows.
 * UV blocking film on windows
 * Window replacements that reduce ultraviolet and visible-light transmission.
 * Dimmers
 * Appropriate-wattage bulbs
 * Use LED lights
 * Store and/or display objects away from windows
 * Use UV filters on light bulbs
 * Use fiber-optic lighting
 * Use conventional incandescent lamps, but at a distance because of their heat generation
 * Use indirect light for storage areas

Types of Light Radiation
Direct daylight is the most damaging to objects because it is the full light spectrum. There are three different types of radiation that have an impact on an object's condition. These three types of light radiation are visible radiation, ultraviolet (UV) or invisible short-wave radiation, and infrared (IR) or long-wave radiation.
 * Visible light radiation is measured in lux or footcandles, and can be measured by a light meter.
 * Ultraviolet (UV) light, is the most damaging to cultural objects. A UV monitor can be used to measure the amount of UV radiation as microwatts/lumen.
 * Infrared (IR) or long-wave radiation exposes objects to both heat and light.

Characterizations of Light Damage
Light is especially damaging to furniture, particularly colored surfaces, fabrics, and finishes. Organic materials like paper, fabric, wood, and leather and also incredibly vulnerable. Light damage is often characterized by:


 * Faded pigment
 * Yellowing
 * Weakening and disintegration of materials
 * Chemical damage
 * Darkening
 * Embrittlement
 * Distortion
 * Stiffening

Additional Reading
Canadian Conservation Institute Getty Museum Lighting Research Victoria & Albert Museum