A disinfecting system comprises a light source having output suitable for use as a germicidal agent, and a power supply for the light source that is adapted to limit the output of the light source to levels adequate for microbial growth control. The light source is operatively housed in fluid-conveying equipment for disinfecting fluids and surfaces therein. The limited output is attenuated by fluid-conveying equipment components disposed within the output range of the light source. The attenuated output provides safe human exposure levels in the vicinity of fluid intake and exhaust portions of the fluid-conveying equipment. The limited output inhibits the degradation of fluid-conveying equipment components disposed within the output range of the light source. The light source may be covered with a thin film or sleeve of material being semi-transparent to germicidal UV wavelengths to control the output of the light source.