The General GUV25403 UV light system is a whole house UV light system. 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.