An elongated light source envelope is disclosed. The elongated light source comprises an inner wall and an outer wall formed around a longitudinal axis. The inner wall and the outer wall may be connected at a first axial end by a first side wall and a second axial end by a second side wall. The inner wall, outer wall, the first side wall, and the second side wall define an enclosed space internal to the envelope. The light source envelope further comprises one or more walls formed between the inner wall and the outer wall to further form at least a first enclosed region and a second enclosed region within the enclosed space. The first enclosed region may be configured to emit a different spectrum of ultraviolet radiation from the second enclosed region in response to excitation of the first enclosed region and the second enclosed region by microwave radiation.