Apparatus for generating ultraviolet light and methods of operating an ultraviolet light source. The apparatus may include a microwave chamber (16) enclosing an interior space, a light source (10) with a lamp head (28) coupled to the microwave chamber (16), an ultraviolet (UV) transmissive member (88) positioned above the lamp face (32) and below the interior space to define a plenum (116) therebetween, and an exhaust system (100) coupled in fluid communication with the plenum. The lamp head (28) has a lamp face (32) through which ultraviolet light (34) and cooling air (30) are emitted. The UV transmissive member (88) is configured to transmit the ultraviolet light (34) into the interior space and to divert the cooling air (30) from the interior space. The exhaust system (100) configured to exhaust the cooling air (30) from the plenum (116).