A UV 
air cleaning and disinfecting 
system has an enclosed 
chassis with an inlet / outlet surface panel on one planar side thereof, and the 
chassis is mounted in the space behind a drop ceiling with its surface panel coplanar with the ceiling surface and facing into the room space. The surface panel has a pair of inlet vent arrays on opposite longitudinal sides of the surface panel from each other, and a pair of outlet vent arrays on opposite latitudinal sides of the surface panel from each other. Arranged in the 
chassis are an 
air blower unit and an array of UV lamps. The positioning of the inlet and outlet vent arrays establish four mutually circulating air streams in a four-leaf-clover pattern in the room space, which obtains a high-efficiency 
throughput of air handled by the 
system. The UV lamp array is arranged longitudinally across the chassis between the inlet ventsat a lower elevational position of the chassis. A pair of air filters is arranged at intake chambers separated by UV-blocking baffles at opposite longitudinal sides of the main chamber housing the 
air blower in the center of the chassis at an upper elevational position from the array of UV lamps. The upward and downward movement of the air through the filters and over the UV lamps toward the center causes swirling movements which enhance the 
exposure of pathogens in the air to UV 
radiation exposure. The surface panel is formed with a series of cascading door sections to allow wide access across the center of the chassis for maintenance of the UV lamps, with a first door section connected to an 
interlock switch for 
cutting off electrical power to the UV lamps and fan when the first door section is opened. The UV-blocking baffles have an angled shape and slits at an upper 
flange thereof covered with fused silica shields. The 
system's chassis is dimensioned to fit on ceiling rails spaced at standard 4 foot length and 2 
foot width intervals. The system can provide 99% or higher inactivation of pathogens in the air with 2 to 7 or more 
air changes per hour for standard sized rooms.