Out on the floor, the coater is humming at line speed and the UV lamp strikes. Before you even reach for the radiometer, look at the arc. That color isn’t cosmetic—it’s a quick field read on the fill gas, vapor pressure, and electrode condition. A cool, blue-white arc usually means you’re getting more short-wave output and higher mercury vapor pressure. A neutral or slightly pinkish tint suggests the arc temperature is stable and the doping is under control. Use that visual as your first gut check. What actually matters on the spec sheet We build mercury UV lamps for paper coating with stable spectral output centered on the 365 nm line, plus solid energy in the 385–405 nm band to match photoinitiators in overprint varnishes and functional coatings. Peak irradiance at the substrate comes down to arc length, reflector geometry, and power density. Spec the lamp to deliver the required energy density at your line speed, not just peak wattage. A properly matched reflector with a dichroic coating keeps heat off the web while shaping the spectral envelope. Why this plays on a mixed finishing line Coating lines often mix offset, flexo, and screen finishing in the same plant. Our lamps are engineered to drop into common curing modules across offset, flexo, screen, and select gravure coaters, with arc lengths and terminals matched to the machine footprint. The payoff is consistent cross-linking: fewer tacky passes, stable gloss, and less energy per cured square meter. You can count on 5,000+ hours of stable output with less than 5% drop when you run inside the rated power window. The details that bite you if you ignore them Match the lamp to the driver. If you run a lamp below its rated current, electrode fall voltage climbs, life shortens, and the spectrum shifts. Run above it, and output decay accelerates—plus you risk cracking the quartz. If the lamp is air-cooled, make sure ozone handling is sorted. On high-speed coaters, double-check reflector focal distance and lamp position so you don’t get hot spots and you keep the dose uniform across the web width.