Light can cause cumulative and irreversible damage to cultural heritage items and needs to be controlled in exhibition/ display and storage environments. There are three categories of light sensitivity used to group objects in collection care: very light sensitive, moderately light sensitive and non light sensitive. Generally, the first of these categories is characterised by organic materials: anything carbon based (plant and animal and synthetic) as light radiation initiates chemical photodegradation. The non light sensitive category is characterised by inorganic materials: such as glass, ceramics, stone and metals.
This method is effective for separating items at high risk from those at low risk; but there are multiple variables at play in a collection which need to be considered before assuming an objects vulnerability. Collections often contain composite objects which do not fit so easily into the organic/inorganic definition. Collections also contain objects of varying condition and significance, the meanings/ value which may be affected by light more readily than expected based on its material characteristics. These variables should be considered along with the material concerns in order to come up with an accurate characterisation of the collections light sensitivity.
In general, all organic materials should be considered VERY LIGHT SENSITIVE or MODERATELY LIGHT SENSITIVE, and therefore susceptible to photochemical deterioration. Inorganic materials are generally NON-LIGHT SENSITIVE. These classifications are useful for assessing which items in your collection are more sensitive to light than others.
It is important to note that many items within a museum collection may be comprised of several different materials, such as a wooden dining chair with a fabric-covered seat. Such an item should be stored and displayed with the most light sensitive element (the textile seat) in mind.
The following materials are considered very susceptible to damage from visible light and UV radiation.
The following materials are considered moderately light-sensitive.
The following materials are considered to be non-light sensitive.
Note again, that it is common for the items listed under the non-light sensitive category to incorporate a painted image, lacquer or varnish surface coating. Where these are present, remember to consider the entire item to be moderately sensitive to light.
Light causes extreme and irreversible damage to many materials, most notably organic materials – those that derive from plants and animals. In a museum, this will include furniture, textiles, prints, books, drawings, manuscripts, wallpaper, dyes and inks, feathers and fur.
Generally speaking, all organic materials, that is, all things that originate from plants and animals are at greater risk of light damage than are inorganic materials such as stone, metal and ceramic objects.