An Ultra-Violet Air Cleaner kills all living organisms inside your HVAC system, cleansing the air you and your family breath. Germs, Bacteria, and Viruses like The Cold and Flu THRIVE inside your HVAC system where it is always dark and wet during cooling mode. A UV light filter will eradicate those organisms, and also Mold and Mildew that can cause respiratory illnesses. This accessory is especially helpful for household members with suppressed immune systems. It our opinion this accessory gives you the most benefit for your dollar and we can not imagine operating an HVAC system without one.