The Enviracaire 3.5 W Germicidal Ultraviolet GTL3 Replacement Bulb is for all Enviracaire Germ Free Humidifiers up to 3.5 gallon capacity. The Enviracaire EUV-13B Humidifier Replacement is a genuine ultraviolet (UV) germicidal bulb that helps to eliminate bacteria growth and contamination. The UV bulb will operate at maximum output for approximately 2,000 hours. The package contains 1 bulb.