An ultraviolet lamp mounted over the evaporator coil to keep biological growth off the perpetually wet coil and drain pan. Valuable for system health and musty odors in humid climates — but it does nothing for dust or pollen.
Air-quality terms map to humidity control in muggy Chesapeake summers, filtration (MERV), ventilation for tighter renovated homes, and duct condition in houses that have seen decades of retrofits.