Dust and other debris as well as ink mist can accumulate on the UV Lamp unit windows. There is a quartz window below each of the two sets of UV Lamp unit.
Inspect and clean the UV Lamp unit windows once a month.
Gloves (for example: Ansell Microflex 93-260)
Cloth-Poly Wipe 10cm x 10cm (lint-free)
Isopropyl alcohol - IPA (>= 98%)
Scraper or razor blade