Lethal to microorganisms, ultra-violet radiation in the range of 2250 to 3020 angstroms is used in a variety of disinfection applications, a process referred to as ultra-violet germicidal irradiation (UVGI). Since the first UVGI system was successfully implemented for disinfecting the municipal water system in Marseilles, France, in 1909, the disinfection of medical equipment using UVGI has been a common and reliable practice. But unlike water- and equipment-disinfection applications, the disinfection of air streams using UVGI has a history of varying success and unpredictable performance.