Fluorescent lights usually combine UV and visible light energy. Tungsten lights usually combine visible and infrared light energy. Newer bulbs vary in the wavelengths they emit. Some halogen lights emit enormous quantities of ultraviolet radiation. Different types of materials are adversely affected at varying rates by light, UV and IR radiation.
Degradation occurs when a material absorbs the radiation.
This occurs if the molecules of the material are susceptible to damage by the wavelength of the light, UV or IR energy. Organic materials are most susceptible to this form of degradation. Generally, the shorter the wavelength, the more damaging the light to the physical stability of an organic material. Light from an overcast sky through glass, which contains high levels of UV radiation, is five times as damaging as a tungsten light at the same level of visible illumination. Recent experiments have shown that ultraviolet radiation weakens physical structures, such as causing paper to embrittle, but visible light is more likely to fade dyes and pigments.