Abstract: A lighting unit adapted to provide a sealed closure in an opening in a Clean-Room ceiling includes a housing which supports one or more light emitting means and has a perimeter structure for supporting the housing in place over the ceiling opening, and a substantially impermeable light diffuser sealingly mounted to the housing by a peripheral frame. A perimeter gasket is retained between and sealingly engages perimeter surfaces of the frame and the opening in the ceiling, and a reversibly adjustable retention device supports the frame and housing together to cause the gasket to sealingly engage the perimeter surface of the frame and the opening in the ceiling. The lighting unit is adapted to prevent or abate leakage of filtered, conditioned air from a room, e.g., a Clean-Room, and is adapted to prevent or abate infiltration of unfiltered, contaminated air into the room from the space above the ceiling.

Abstract: A modular, low-profile ceiling air filtration unit is disclosed having a diffuser plate with an unperforated zone along one edge, the remainder of the plate being perforated. A blower in the unit plenum directs air toward the end of the plenum having the unperforated zone. Turbulent air impinging on the housing end wall is prevented from passing through to a filter by the unperforated zone of the diffuser plate.