Environment - Light
The Effects of Light
Light degrades organic materials, which include anything that comes from plant or animal sources, as well as plastics and dyes. Light speeds up oxidation and thus the chemical break-down of these substances. Oxidation is a complicated set of interactions which degrades the polymeric structure of organic materials. Ultraviolet (UV) light, invisible to the human eye, is more energetic than visible light and therefore more damaging.
UV light is especially destructive to papers containing lignins, such as newsprint or other papers made from unpurified wood pulp. It is also a major cause of color fading; some organic colors are especially affected by intense or prolonged exposure to UV sources. Most traditional photographic prints are vulnerable to UV as well.
Sunlight must never fall on a glazed picture—the impact is immediate and dramatic. Localized heating and drying of materials can quickly cause permanent damage.
“The instability of the microclimate in pictures that are briefly exposed to shafts of sunlight through windows is particularly striking, and leads us to emphasise that ambient climate control in a gallery gives no protection against direct sunlight,particularly on objects enclosed behind glass.” Tim Padfield et al, “How to Protect Glazed Pictures From Climatic Insult”
Sources of Light
Usually we are dealing with sunlight, fluorescent lights or various incandescent lights. Sunlight generates more UV than the other sources; about six times as much as tungsten incandescent lamps. Daylight, even with the UV removed, can be assumed to be about three times as damaging as tungsten incandescent sources. In terms of UV emission, fluorescent lights, both tubes and Compact Fluorescent Lamps (CFLs) fall in between daylight and tungsten lights, and are considered a serious UV threat to art materials. Generally speaking, if tungsten incandescent light is the only light source, UV filtering is unnecessary, but other incandescent light sources, such as quartz halogen lamps, emit significant ultraviolet radiation and should be filtered at the source or in frame glazing. Since tungsten incandescent bulbs are being phased out, all current sources of light should be considered to be possible emitters of UV radiation at levels harmful to works of art. LED lamps, which may be the lighting of the future, do not emit significant UV.
Filtering of UV Light
There are ultraviolet filtering sleeves for fluorescent bulbs and thin UV filtering films which can be affixed to window glass. The effective lifespan of sleeves and films is unknown.