The General MS24ER Microbe Swatter UV light system is a whole house UV light system. This unit is typically 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.