Many practical suggestions are made on how to reduce damage caused by light. Methods of filtering out ultraviolet radiation and ways of controlling illumination are discussed, and British suppliers of U.V. absorbing filters and instruments for light measurement are listed. Illumination valves of 150 lux for materials of intermediate sensistivity and 50 lux for sensistive materials and the need to reduce the overall time of exposure are recommended. Practical considerations concerning daylight, color rendering, direct versus diffuse illumination, color temperatures and lighting for photography and television are also briefly covered.