Key takeaways
- Far-UVC is ultraviolet light at about 200 to 230 nm. Most devices use 222 nm krypton-chloride lamps.
- Laboratory studies show very low doses inactivate airborne viruses, including influenza and human coronaviruses.
- Far-UVC barely penetrates the outer dead layer of skin or the tear film of the eye, which is why it is being used in occupied spaces.
- Good device design matters: filtering out longer wavelengths and managing ozone are part of doing it properly.
Why conventional UV-C has limits
Ultraviolet light has been used to disinfect air and surfaces since the 1940s, and there is strong evidence that UV-C reduces the spread of infections carried on surfaces and in the air. Most germicidal systems use light at around 254 nm, which damages the genetic material of bacteria, viruses and fungi so they can no longer multiply.
The problem is that 254 nm light can also harm human skin and eyes. That is why conventional UV-C robots run only in empty rooms, and why upper-room UV fixtures are shielded so the light stays above people's heads. Every minute a room must stand empty is a minute it cannot be used, and the air is only treated while no one is there.
What makes far-UVC different
Far-UVC sits at the short end of the UV-C band, between roughly 200 and 230 nm. Light at these wavelengths is absorbed very strongly by proteins, so it travels only a few micrometres into biological material. Researchers at Columbia University explain that this is far too short to reach the living cells under the dead outer layer of the skin (the stratum corneum) or beneath the tear layer of the eye.
Bacteria and viruses, however, are smaller than that distance. Far-UVC can pass through them completely and inactivate them. In simple terms, the light is stopped by the body's own protective surface layers but not by microbes.
What the studies show
In a 2018 study published in Scientific Reports, the Columbia team exposed airborne influenza A (H1N1) virus to 222 nm light in a chamber designed to mimic droplets from coughing and breathing. A very low dose of about 2 mJ/cm² inactivated more than 95% of the virus.
A follow-up study in 2020 tested two airborne human coronaviruses. Doses of 1.7 and 1.2 mJ/cm² inactivated 99.9% of the viruses. Based on these results, the authors estimated that continuous far-UVC within the exposure limits of the time could reduce airborne coronavirus in an occupied room by about 90% in 8 minutes and 99.9% in around 25 minutes.
The effect is not limited to viruses. Researchers in Japan tested 222 nm light against a wide range of pathogens found in hospitals, including Staphylococcus aureus, Pseudomonas aeruginosa, E. coli, Candida albicans and C. difficile spores. It worked as well as 254 nm on bacteria, yeast and viruses, and was more effective on bacterial spores, although it was weaker against mould spores and hyphae.
A 2021 review that gathered more than 100 papers from the past century reached a similar conclusion: 222 nm light is strongly antimicrobial, needing on average about 1.3 times the dose of 254 nm light for the same reduction.
What to look for in a far-UVC system
The International Ultraviolet Association's review of far-UVC highlights a few practical points that separate a well-designed system from a poor one:
- Spectral filtering. Some lamps also emit light above 230 nm. Filters that remove these longer wavelengths are important for safety.
- Ozone. Some far-UVC lamps can generate small amounts of ozone. This is manageable, but it should be measured when the installation is designed.
- Dose planning. The right number and placement of devices depends on the room, its furniture and how it is used.
Where far-UVC fits in a hospital
Far-UVC does not replace cleaning, hand hygiene or ventilation. Its value is that it keeps working between cleaning cycles, while staff and patients are present. That makes it well suited to operating rooms, intensive care units, isolation areas, emergency departments and waiting rooms, where people are always coming and going.
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References
- Welch D, Buonanno M, Grilj V, et al. Far-UVC light: a new tool to control the spread of airborne-mediated microbial diseases. Scientific Reports. 2018;8:2752. doi:10.1038/s41598-018-21058-w
- Buonanno M, Welch D, Shuryak I, Brenner DJ. Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses. Scientific Reports. 2020;10:10285. doi:10.1038/s41598-020-67211-2
- Narita K, Asano K, Naito K, et al. Ultraviolet C light with wavelength of 222 nm inactivates a wide spectrum of microbial pathogens. Journal of Hospital Infection. 2020;105:459–467.
- Hessling M, Haag R, Sieber N, Vatter P. The impact of far-UVC radiation (200–230 nm) on pathogens, cells, skin, and eyes: a collection and analysis of a hundred years of data. GMS Hygiene and Infection Control. 2021;16:Doc07.
- International Ultraviolet Association. Far UV-C Radiation: Current State-of-Knowledge. IUVA white paper.
This article summarises published research for general information and is not medical advice. Selection and use of disinfection devices should follow the manufacturer's instructions and local regulations.