The Honeywell UC18W1004 Snaplamp replacement UV bulb is designed for the Honeywell UV100E1043 Air Treatment System. The UC18W1004's UV light penetrates microorganisms and breaks down molecular bonds causing cellular and/or genetic damage, resulting in the germs being killed or sterilized, leaving them unlikely to reproduce. Honeywell UV bulbs are made from sodium-barium silicate and do not produce ozone, and the SnapLamp™ feature reduces bulb costs by reusing the bulb handle. Safe design prevents lamp from lighting unless base is correctly mounted on HVAC duct, and the sealed unit prevents accidental installer/homeowner contact with high voltage and ultraviolet rays. Bulb is 7-7/16 inches in length. Bulbs effective life is 8000 hours. Fits Models UC100A1005, UC100E1006, UV100A1000, and UV100E1043.