A UV lamp is a scheduled replacement, not a failure item. Its UV-C output falls steadily through life while the lamp continues to light normally, so a reactor with visibly working lamps can be well below its dosing duty. Replacement is made on elapsed operating hours against the measured intensity trend, not on the lamp going out. Order against the reactor model, and handle the new lamp by its ends only — skin oils fired onto the envelope at operating temperature devitrify the quartz and cost output permanently. Match the lamp to the reactor model rather than to physical size: Berson has built more than one lamp rating into reactors of similar dimensions, and a lamp that fits mechanically may not be the one the plant was dosed around.