A ultraviolet (UV) steriliser assembly comprising a UV source (10) configured to emit ultraviolet light of a range of wavelengths and a reflector (16) associated with the UV source. The reflector (16) is configured to permit transmission therethrough of identified wavelengths of light in order to control the wavelength of light reflected by said reflector. Preferably the reflector includes a dichroic coating (11). Also claimed is a disinfection method including providing a reflector with a coating or composition that permits transmission therethrough of identified wavelengths of UV light in order to control the wavelength of light reflected by said reflector, and arranging the reflector in combination with a broad spectrum UV source. A media to be treated by the method is either located in front of the reflector or behind the reflector dependent on which light wavelengths contacting the media have the highest germicidal strength.
