Light

Exposure to intense light causes fading (especially of inks and colors), darkening and yellowing (especially of paper containing wood and lignin), and the weakening of fibers. Both sunlight and artificial light (especially fluorescent) are sources of ultraviolet, the most harmful of the light wavelengths. However, all direct light is damaging to some degree. Materials are at their most vulnerable when exposed on long-term display or when stored under strong, constant light, for example, in front of a window.

The amount of light is measured in lux, or footcandles, with one lux (or lumen) equivalent to 0.09 footcandles. A 150-watt incandescent light bulb will produce 50 lux at a distance of one meter. In storage areas, lights should always be turned off when the area is not in use; when turned on, lights should be limited to 100 lux unless materials are covered. Materials on exhibition should generally not be subjected to light stronger than 80 lux. In addition, ultraviolet shields should be employed if the lights are fluorescent. Window light should be filtered through screens or blinds.

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