UV radiation and light both cause discolouration and damage to the surface of an object. It is possible to eliminate the UV portion of a light source but we must retain some visible light in order to be able to see the object on display, so therefore must permit a certain amount of damage to occur to an object over time on display. We can limit this damage by controlling this light exposure but cannot not eliminate it altogether. This can be done in two ways:

• Reduce the quantity of light an object is exposed to
• Reduce the amount of time the light is exposed to an object

Recommended levels:

Exhibits	maximum
Objects specially sensitive to light Textiles, costumes, water-colours, tapestries, prints and drawings, manuscripts, miniatures, paintings in distemper media, wallpapers, gouache, dyed leather. Most natural history exhibits including botanical and entomological specimens, fur and feathers.	50 lux
Objects sensitive to light Oil and tempera paintings, undyed leather, horn, bone and ivory oriental lacquer.	200 lux
Objects insensitive to light metal, stone, glass, ceramics, jewellery, enamel and objects in which colour is not of high importance (e.g. wood) may be illuminated at higher levels.	300 lux

At the lowest level, 50 lux, artificial light must be used as daylight cannot be controlled adequately to enable this level to be maintained. The eye will adapt to this level of light and see sufficient detail in an object if there is a separation of this material away from brighter lit areas, and an opportunity for the eye to adjust to this low level. This can be achieved by placing the specially sensitive exhibits in a separate room entered via a darkened passage way. When using low light levels, take care to also light the room as well as the exhibits however, if only the exhibits are lit the room will be perceived as uncomfortably 'gloomy'.

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