On the press floor, when UV curing falls apart, you often find the culprit where you least expect it: a thin coat of oily mist and ink residue on the lamp surface and reflector. That film steals UV photons before they ever hit the substrate. The result is weak cross-linking, adhesion that gives up, and unplanned stops. You’ve seen it—tacky ink, pinholes, gloss that drifts job to job. The answer isn’t more power. It’s keeping the optics clean and consistent. What actually matters UV curing comes down to spectral output and the energy density delivered at the substrate plane. Mercury vapor lamps hit their peak at 365 nm, with strong output around 254 nm and 436 nm to match what the photoinitiator needs. Reflectors with dichroic coatings shape the spectral energy distribution and keep peak irradiance up by kicking IR out of the beam. When residues coat the quartz envelope, reflectivity drops and output falls off. Grab a radiometer and you can measure it: irradiance in mW/cm² and dose in mJ/cm². By the time operators notice a quality shift, output has typically slipped 15–30%. Why this works in practice A daily clean brings photon flux back to where it should be and stabilizes the curing window. Wipe the lamp and reflector with isopropyl alcohol and a lint-free cloth, then look for haze. That routine cuts premature lamp aging caused by hot spots and thermal stress, and it keeps the reflector geometry doing its job. Teams that stick to a schedule get stable dose, fewer rejects, and stretch lamp life by about 30%. That means more uptime, fewer lamp changes, and print quality that holds steady shift after shift. What to keep in mind Always let the lamp cool and power down before you clean. Wear gloves when handling quartz—fingerprints bake into films. Confirm electrical limits and connector compatibility with your curing module, and make sure the arc length matches the reflector focal plane. Here’s the trade-off: harsh solvents and aggressive cleaning tools can scratch quartz and degrade the dichroic coating, which accelerates output loss. Keep a log of irradiance readings so cleaning and replacement are driven by data, not guesswork.