Radiant energy , the most familiar type of which is visible light, can initiate or accelerate damage by chemical reaction, especially in organic materials. Ultraviolet light is the most harmful, causing irreversible damage by initiating chemical reactions on a molecular level. Both fluorescent lamps and daylight may contain high levels of ultraviolet light. Daylight also contains infrared radiation, or heat, which can initiate and accelerate damaging chemical reactions. Visible light includes all the wavelengths of radiant energy that let us see color.
Relative humidity refers to the amount of moisture in air.
Organic materials absorb or give off moisture in a continuous attempt to achieve equilibrium with the atmosphere. Inorganic materials usually are not affected by relative humidity levels unless they contain salts or are otherwise unstable. Metals, however, are best preserved at low relative humidity. Serious damage can occur when materials are subjected to dramatic, sudden changes in relative humidity over short periods. Temperature is significant because it affects relative humidity.