An ultraviolet ozone generating device has a tubular enclosure with a light tunnel or box situated within the enclosure and containing a cold cathode UV lamp. An input duct and an output duct, each comprised of a 90 degree ell tube, prevent direct line of sight escape of the UV radiation from the device but do not restrict the air flow through the light tunnel. In order to control the output level, the lamp is powered to pulse on and off, and the duty cycle of the lamp power is controlled through a control knob which can be adjusted as desired. The enclosure is constructed so that any condensation forms and drips to the outside.