2020 saw the world rocked by widespread turmoil, as a virulent new pathogen started claiming lives around the globe. The COVID-19 pandemic saw a rush on masks, air filtration systems, and hand sanitizer, as terrified populations sought to stave off the deadly virus by any means possible.
Despite the fresh attention given to indoor air quality and airborne disease transmission, there remains one technology that was largely overlooked. It’s the concept of upper-room UV sterilization—a remarkably simple way of tackling biological nastiness in the air.
Warm Glowing Killing Glow
Upper-room UV systems sound kind of like science-fiction technology. They nuke nasty pathogens in the air, and do it while emitting a faint and weird-colored glow. In reality, they’ve been quietly hanging around for about 80 years. The idea is straightforward enough—you just shine UV-C light in the unused overhead zone of a room to zap airborne pathogens before they get inhaled by fragile humans!
Upper-room UV sterilization keeps the harmful UV-C light away from the occupants in the room. Credit: CDC
The concept came about as a direct result of 19th-century research that determined sunlight inhibited the growth of undesirable microbes and pathogens. Later work determined that light in the UV-C range of wavelengths is remarkably good at killing both bacteria and viruses, making it ideal for sterilizing purposes. The UV-C range is from 100 to 280 nanometers, but peak sterilizing action occurs around the 250-270 nm range. The primary method of action is that the UV-C light creates defects in DNA molecules that kill or inactivate microscopic organisms, including bacteria and viruses. It’s perfect for tackling all sorts of nasties, from measles to SARS to TB.
Unfortunately, that also means that UV-C light isn’t always safe to use around humans. Just as it hurts microbes, this light is also harmful to our skin and eyes in exactly the same way. Indeed, a prime example of this was a 2023 event that allegedly accidentally used UV sterilization lamps as decorative blacklights. While UV-C light is used in a wide range of sterilization applications, most keep the light hidden or localized to avoid direct human exposure.
Upper-room UV-C installations are particularly interesting, though, for their simplicity. To avoid dangerous exposures, these installations simply place the sterilizing lamps up high in a room and direct their light into the upper level of air. As long as the UV light output is directed into the top level of the room, well above the heads of any occupants, it can sterilize the air effectively with little risk of harm.
UV-C lamps typically have peak output at 254 nm, but they also output some light in the visual spectrum that gives them a characteristic green glow—as seen on this Phillips wall-mount unit. Credit: Phillips
For this reason, these systems are typically installed in places like schools, hospitals and other public buildings, where ceiling heights are high enough to make such installations safe. CDC guidelines suggest minimum ceiling heights must be at least 8 feet for these installations, though 8.5 feet is preferred. For most people, that’s high enough not to cause trouble, but if you’re one of the taller players in the NBA, you might want to take note.
Upper-room UV systems treat a massive volume of air simply by sectioning the room into a germ-killing overhead zone and a safer lower zone where people breathe. Natural convection, HVAC currents, and even a simple ceiling fan help keep the air circulating upward, doused by the UV field, and then returned to the lower portion, scrubbed clean. At least a minimal level of circulation is required in order to ensure all the air in a given room is being treated. Power levels required are relatively low. A 2015 study suggested a total output of just 15-20 milliwatts is enough per cubic meter of room volume, assuming adequate air mixing in the space.
Ultimately, though, proper sizing and safe installation are critical for creating an effective and safe sterilization system. UV-C is safe enough when used properly, but get it wrong, and you’ll see plenty of sore eyes and red skin almost immediately. The key is blocking direct and reflected UV light from reaching the lower zone of the room. Louvered fixtures with carefully aimed beams are necessary in rooms with lower ceilings, while more open fixtures are more for lofty spaces where they can blast UV upward without frying everyone’s eyeballs. Proper metering must be done at the time of installation to ensure light concentration is high enough in the sterilization region, and below safety limits in the occupied region. It’s also important to ensure the lamps are switched off for maintenance or if anyone is entering the upper zone of the room for any reason.
It might sound high-tech, but this approach predates modern pandemics by decades. It was already showing its effectiveness against diseases like measles and tuberculosis as far back as the 1930s and 1940s. Early success was found at Duke University in 1936, where post-surgical infections were cut from 11.62% to just 0.24% with the use of an operating room eqiupped with UV-C equipment. Later, a 1941 study determined that UV-C delivered by mercury-vapor lamps had drastically reduced measles transmission in classrooms.
This installation used bare UV-C bulbs, directing them with louvers or hiding them in a perforated sub-ceiling. Note the eerie green glow. Credit: research paper
Given its efficacy, you might think that upper room UV-C installations would be everywhere. Subways, airports, schools, hospitals, and malls could all benefit from this technology. However, it would require some investment and ongoing maintenance, and it seems that simple cost is too much to bear.
For whatever reason, upper-room UV remains an obscure technology, seldom discussed and rarely used. Here we are, after countless deadly airborne disease outbreaks, still largely ignoring a century-old technology that actually works. The simplicity is staggering—slap a UV fixture on the wall near the ceiling, tune it so that zero harmful light hits the occupants, and let it run. It’s not a silver bullet for all air quality concerns, and you still need ventilation, of course. But for dealing with nasty airborne pathogens? It’s hard to imagine an easier solution than upper-room UV. The only real question left is, why aren’t we using it everywhere?
This articles is written by : Nermeen Nabil Khear Abdelmalak
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By Nermeen Nabil Khear 
Ultimately, though, proper sizing and safe installation are critical for creating an effective and safe sterilization system. UV-C is safe enough when used properly, but get it wrong, and you’ll see plenty of sore eyes and red skin almost immediately. The key is blocking direct and reflected UV light from reaching the lower zone of the room. Louvered fixtures with carefully aimed beams are necessary in rooms with lower ceilings, while more open fixtures are more for lofty spaces where they can blast UV upward without frying everyone’s eyeballs. Proper metering must be done at the time of installation to ensure light concentration is high enough in the sterilization region, and below safety limits in the occupied region. It’s also important to ensure the lamps are switched off for maintenance or if anyone is entering the upper zone of the room for any reason.