To reduce deterioration of museum objects some illumination levels for light sources in museums and galleries are given by the illumination intensity (lux), which is calculated both with the relative luminous efficiency, effect on the human eye, and energy distribution of light sources. Reports on findings recorded since 1930 on the action of light on colorants applied to museum objects, explains the spectral response or reactivity of the colorant to radiation, and discusses quantitative problems such as the fading rate and the amount of fading. -- AATA