The two primary benefits to using UV light are disinfecting air and preventing growth of mold. The UV light radiates a surface to keep mold from growing in that area and disinfects the air stream as it passes through the HVAC system. In one pass over the UV bulb, a high disinfection rate is not normally accomplished in the air stream. With repeated circulation of air through the system, a major disinfection rate is accomplished, making use of UV light very positive.