An apparatus comprising a discharge lamp configured to emit ultraviolet and visible light and an optical filter 122 arranged adjacent to the discharge lamp. The optical filter comprises multiple panels which attenuate visible light. The multiple panels are fused together or joined by support strips and the spacing between the parallel sections of the u-shaped discharge lamp is larger than the width of the fused areas and/or the support strips. A safety mechanism is provided that comprises a room occupancy sensor to determine whether people are present in the room in which the apparatus is arranged. Also claimed is an apparatus comprising a pulsed discharge lamp 104 configured to emit ultraviolet and visible light and an optical filter 122 arranged adjacent to the discharge lamp, wherein the optical filter comprises multiple panels of the same material which attenuates visible light. The optical filter panels may be formed from optical filter glass materials or may be optically transparent with films which attenuate visible light disposed thereon. The optical filter passes the majority of UV light of between approximately 260nm to 265nm.
