For best results, replace every 18-24 months. After that, the bulb may be lit but the output is too low. Easy to follow replacement instructions included with your purchase, or have a local service technician do the work instead. Either way, keep your UltraPure System working the way it was designed to. IMPORTANT Notes / Restrictions: Used On: 1998 - Current Ultra Pure and Crystal Zone Water Management Systems The following .PDF URLs include details about the UV Ozone Lamp and it's function within Dimension One's Ultra Pure / Crystal Zone system: http://spapalace.com/products/pdf/D1_ACC_OZONE.pdf http://spapalace.com/products/pdf/D1_ACC_OZONE2.pdf