On the floor, “print-and-dry” in screen isn’t a tagline. It’s what keeps the line moving. If the cure can’t keep up, the conveyor starts backing up, pinholes show up, and ink transfer falls apart. High-response UV is the hinge on the whole operation. The real question is which source gives you repeatable, instant cure: the mercury vapor lamp or the UV LED array. What matters, technically Mercury lamps put out a broad spectrum, with strong peaks at 365 nm, 405 nm, and other lines, so you hit multiple photoinitiators at once. With a dichroic reflector and stable arc control, peak irradiance stays predictable across the arc length, and you get the kind of energy density that can drive through thick deposits. UV LED cures at narrow wavelengths—typically 365 nm, 385 nm, 405 nm—turns on and off almost instantly, runs cooler, and has a slow, controlled lumen-degradation curve. You get tens of thousands of hours of life, and output stays stable right at the die. Energy use drops because there’s no warm-up and no idling power. Why it works where we work In screen, fast response is what keeps production continuous. LEDs hit full output the second you need it, so the first sheet cures the same as the hundredth, and you stop losing time to lamp warm-up. Mercury still shines when the ink stack is thick and needs deep cross-linking, or when multiple initiators need broad-band excitation. That high peak irradiance can push cure through pigments and substrates that LEDs have a harder time with. If you’re chasing consistent, low-heat runs with a high duty cycle, LED makes sense. If the deposit geometry and spectral demand call for brute-force through-cure, mercury is the call. Here are the details you can’t skip LED curing forces you to get the optics right: a uniform, high-peak profile with enough mJ/cm² across the web. Expect to manage heat more tightly—heat sinks, airflow, and mounting tolerances all shape output and life. Mercury systems mean reflector alignment and a planned lamp replacement schedule; output falls off as the arc ages, and ozone management is part of the design. Match the spectrum to the photoinitiator, then validate with a radiometer: measure peak irradiance and energy density at line speed.