Artwork exposed to Ultraviolet light can cause irreversible damage by a process known as photo-oxidation. Works on paper are usually the most sensitive to this kind of damage. For the media such as watercolours, this results in fading and in the paper itself, this results in the degradation of the paper at a molecular level, causing the cellulose paper fibre to breakdown. In extreme cases, this can results in the loss of the artwork entirely.
Therefore, Ultraviolet protection glass is recommended especially for works on paper such as watercolours, prints and photographs. The risk can be further reduced by not placing the artwork where it will receive a high dose of ultraviolet radiation. This can mean not placing it near a window in direct sunlight, or very close to an intense artificial light source. LED lighting could be considered in these cases as they produce a very small amount of UV light.
In some museums, artwork will often have a lux limit for the year, which is the maximum amount of light it should be exposed to over the course of a year. Watercolours, for example, will often be shown in low light conditions and kept in the dark for periods when they are not on display.