Berson reactors with an automatic wiper sweep the outside of the quartz sleeve on a timed cycle. Scale, iron and organic film attenuate UV-C before it reaches the water, so a wiper that has stalled or is wiping unevenly shows as falling measured intensity on lamps that are still good. The holder carries the wiper rings on the rod and sets the pressure they bear on the quartz sleeve. Too little contact and deposits survive the sweep; too much and the rings and the sleeve both wear. Replace the holder and the rings together — a new ring in a worn holder does not restore the original contact.