a uv irradiation apparatus for treating fluids employs light transmission tubes having uv lamps therein and a smooth fluorocarbon resin layer over the outside surface of the tubes . for example , a teflon ® sheath or film over the outside surface of the tubes may be employed . a tightly fitted scraper ring with an attached cleaning fluid chamber reciprocates over the coated tubes to clean contaminants from the surface thereof , which contaminants would otherwise impair the uv irradiation ability of the lamps within the tubes .