A mains electricity (AC-powered) device intended for medical purposes that is used to destroy bacteria in the air by exposure to ultraviolet radiation from a light source, consisting of, e.g., a low pressure mercury (Hg) vapour tube that emits ultraviolet radiation as well as visible light. It may also destroy bacteria by other means, thereby reducing concentration of airborne droplet nuclei that carry live microorganisms. It could typically be used to prevent the spreading of tuberculosis (TB).