A food plant in Kaohsiung told us: "We installed UVC lamps, yet the pre-shipment colony-count spot checks still occasionally come back over the limit." When we went on site, the lamps were lit and did reach the conveyor belt; the real problem was that the belt ran too fast, so the product simply didn't spend enough time under the UVC. Very often "the disinfection isn't as effective as expected" doesn't mean the lamp is broken — it means the dose is insufficient. Get your head around dose, and you'll use UVC correctly.
Dose = Irradiance × Time
Disinfection effectiveness depends on the accumulated UV dose the microorganism receives, measured in mJ/cm². It equals irradiance (radiant intensity) multiplied by exposure time, so shining brighter or shining longer both raise the dose.
That said, the dose needed to reach a given kill rate varies a great deal between microorganisms. According to published research, most common microorganisms can be effectively inactivated at around 10 mJ/cm², while more stubborn strains may need 20 mJ/cm² or more; for viruses, for instance, studies have reported that SARS-CoV-2 reaches 3-log (99.9%) inactivation or better at roughly 3.7 mJ/cm². The point is that if the dose falls short, the kill rate won't climb, and every additional level of log reduction demands a stepwise increase in dose — so before designing, first decide what you're trying to kill and to how many logs.
Irradiance Falls Off Quickly with Distance
A lamp's irradiance drops faster the farther away you are, roughly following an inverse-square relationship with distance — so with the same lamp, the intensity reaching a surface at 10 cm versus 50 cm can differ by more than twentyfold. That's why the design can't just watch the lamp's wattage; you also have to factor in the actual distance between the lamp and the target. It's also why mounting a lamp at the top of a duct, too far from the water or material surface below, often delivers a real-world result well below the catalog figures.
Moving Air and Water: Residence Time Is Key
Back to that food plant: the residence time that air or water spends passing through the UVC zone directly determines the accumulated dose. Once the air or water throughput is too large and the flow too fast, a single pass simply doesn't collect enough dose. So the correct approach for duct or water disinfection is to work backward from the air or water throughput to the required number of lamps, the lamp length and an appropriate flow rate, so that every portion of air or water accumulates the target dose as it passes through — and that plant, in the end, solved its problem by slowing the conveyor and lengthening the irradiation zone.
Lamps Degrade and Need Maintenance
A UVC lamp's output slowly declines with operating hours, and oil or scale on the quartz sleeve blocks light as well, quietly dragging the actual dose down — so replace lamps on schedule according to their rated life and clean the sleeves regularly. Don't let "it still looks bright" fool you: UVC is nearly invisible to the human eye, so brightness is no proof of strength.
TingHao Technology is based in Nanzi, Kaohsiung, serving Kaohsiung, Tainan, Pingtung and southern Taiwan, and we estimate the lamp count and layout from your air throughput, water throughput or surface requirements. Feel free to share your site conditions so we can talk it through.