An ultraviolet light irradiation apparatus providing combined mechanical and chemical cleaning of light irradiation tubes for removing radiation blocking precipitates from the surface of the tubes. A scraper ring is fitted to the outside of each of the tubes and includes a chamber for receiving a relatively small quantity of cleaning solution. The scraper rings are reciprocated in a sliding action along the tubes which action synergistically acts with the cleaning solution to remove precipitates from the tube surface including fine particles lodged in concave pits in the tube surface.