All light causes organic objects, such as textiles or taxidermy, to fade. Some objects and materials fade faster than others. You need light to see the exhibits. But how much light is okay?
Light Budgets (Lux Hours)
Conservators set limits to how long an object is exposed to light. This is called a light budget and is measured in lux hours. A lux hour is a multiplication of an hour of exposure by the intensity of the light measured in lux.
Lux hours = amount of light (lux)
X the hours of exposure
Reducing the amount of light in exhibits extends the amount of time an object can be displayed. There are several ways to go about controlling light.
A shade is used to block natural sunlight from damaging this specimen.
An easy way to control light is to block it before it reaches an object. Sunlight, which contains damaging ultraviolet and infrared light, should not fall directly on objects. Window shades and curtains eliminate all light by blocking the sun completely. Light can also be blocked by many kinds of filters. The film on windows in this gallery filters out all ultraviolet light (see cartoon at top), but lets in some visible light. Plexiglas™ can be specially treated to filter ultraviolet light.
Photo: A shade is used to block natural sunlight from damaging this specimen.
Museum conservators periodically exchange objects on exhibit for similar objects to reduce the possibility of light damage.
Some materials are so light sensitive that any exposure to light will cause damage. When this is the case, a photograph or replica should be displayed instead of the real thing.
Lighting on demand
Very light sensitive objects, like these extinct passenger pigeons, are lit on demand. Visitors trigger motion sensors to turn on lights or push buttons to illuminate an exhibit.
Photo: Passenger pigeons