In outdoor advertising, faded banners aren’t just ugly—they eat into your margins. If you’re running PVC or coated canvas through UV offset, flexo, or screen lines, the question that matters is measurable: how many years of sun can that cured ink film hold before the color shifts? The answer has less to do with the ink label and more to do with the energy density you deliver at cure and how completely the photoinitiators convert. Here’s what actually matters on the technical side. For outdoor durability, the lamp has to put out stable spectral output right where the photoinitiators absorb—usually 365nm and 385nm—while keeping peak irradiance high enough to punch through pigmented layers. We size lamps by irradiance (mW/cm²) at the substrate plane, total delivered energy (mJ/cm²), and how stable that output stays over time. A high-pressure mercury vapor lamp with a dichroic reflector concentrates output in the 365–395nm band, giving you deep cross-linking instead of a skin that cures on top and stays soft underneath. For pigmented inks, target 800–1200 mJ/cm² on the substrate. That drives conversion above 90% and keeps unreacted monomer from yellowing in the sun. Why this approach holds up on banners. Outdoor inks are loaded with pigments that chew up UV. If the cure is under-dosed, leftover photoinitiator and oligomers migrate and degrade, and you get chalking and fading within months. Match the lamp and reflector geometry properly, and you can finish polymerization in one pass—even at 100–150 m/min—leaving a film that resists abrasion and solvents. Accelerated weathering on QUV-A (340nm) and xenon tests shows fully cured UV ink films on coated canvas can hold color and gloss beyond three years of equivalent Florida exposure, as long as you verify lamp output with a spectral radiometer and keep irradiance within ±5% of the starting level. A few shop-floor details you can’t skip. Lamp output drops as electrodes wear and mercury depletes; plan on swapping lamps at 1000–1500 hours if you want consistent weatherability. Check your substrate’s temperature tolerance—PVC will warp if the IR load gets too high. Use ozone-free quartz envelopes and keep reflector alignment tight so you don’t get shadowing near the print head. **Match the lamp spectrum to the ink chemistry.**Go with 365nm when you need deep cure, and 385–395nm for faster surface cure with less heat. Confirm against your ink supplier’s photoinitiator absorption curve.