A UV ozonator uses an ultraviolet florescent bulb to create, or convert oxygen to, ozone. The frequency of the light output has to be very specific to produce ozone. Over time, the frequency changes. Generally a UV ozonator will product acceptable levels of ozone over 10,000 hours of use. After that, the bulb will still light, but it won't be producing much ozone. Heck, the bulb could continue to light up for 100,000 hours.... but it wont be producing ozone.