This pamphlet was written as a general guide with practical advice for museum directors and curators, stimulated by the considerable interest generated by the report of Genard (197). Any light may be harmful to museum objects. Those items most affected (essentially organic materials) and least affected are listed. The extent of deterioration depends on intensity, time of exposure, spectral character of the lamp and the absorption characteristics of the object. The near UV (between 320 and 400 nm) radiation is less harmful than far UV of equal intensity. Some of the emission characteristics of fluorescent lamps described by Genard are restated. There is discussion of the ability of regular window glass, diffussing plastic sheeting and reflected light to filter UV radiation. The pamphlet concludes with practical advice on ways to minimize deterioration, including the necessity for reducing humidity and temperature since these factors can accelerate deterioration due to light.