The General GUV161 UV light system is a wholehouse UV light system. This unit is typicaly installed in the duct system so it can kill germs as they pass through its light output. UVC germicidal lamps significantly reduce levels of harmful bacteria, viruses, mold spores and other microorganisms for healthier indoor air. The air we breathe outdoors is purified naturally by our sun! Ultraviolet (UV) light naturally kills microorganisms in the air we breathe that can cause health problems. Like all UV light systems the lamp MUST be replaced every 12 months for optimal performance.