Light accelerates library and archival material degradation. It contributes to cellulose fibre weakening and embrittlement and can cause bleach, yellow, or darkening of paper. Media and dyes are often induced to fade or change colour, affecting the legibility and/or appearance of documents, photos, works of art, and bindings. Any light exposure, except for a short time, is harmful, and the damage is cumulative and permanent.
Since total damage is a function of both exposure intensity and length, illumination should be kept as low as possible for the shortest amount of time feasible (consistent with user comfort). Materials should preferably only be exposed to light when in use.
Air Quality - Pollutants contribute heavily to library and archival material degradation. Gases and particulates are the two significant forms of contaminants. Gaseous pollutants catalyse harmful chemical reactions, especially sulphur dioxide, nitrogen oxides, peroxides, and ozone, leading to acid forming in materials.
It is complicated and complex to regulate air quality and relies on many inter-related factors. Various criteria have been proposed for air quality.
In the preservation of library and archival collections, temperature and relative humidity regulation are important because unacceptable levels of this lead significantly to material breakdown. Heat accelerates deterioration: with each rise in temperature of 18°F (10°C), the rate of most chemical reactions, including deterioration, is roughly doubled.