Ultraviolet (UV) light in various forms has been used widely in the last century to disinfect water, air and surfaces, but its use in public spaces is increasingly common since the COVID-19 pandemic. In a new study published in Applied and Environmental Microbiology, University of Colorado researchers report finding the sweet spot in the UV spectrum that is both extremely effective at killing the virus and also safer for human exposure, allowing airports and entertainment venues to disinfect even when people are present. The researchers found that while the virus was quite susceptible to UV light in general, a specific wavelength of far-ultraviolet C at 222 nanometers was particularly effective, while remaining safe for human skin and eyes. The highest disinfection rate was from krypton chloride (KrCl) excimers, a low-pressure, mercury-vapor lamp.

“Of almost every pathogen we have ever studied, this virus is one of the easiest, by far, to kill with UV light,” says senior author Karl Linden, professor of environmental engineering.

Also, researchers at the United Kingdom’s Addenbrooke Hospital, in Cambridge, studied the use of portable high-energy particulate air (HEPA) filters in crowded COVID-19 wards. They found that the relatively inexpensive machines effectively removed COVID-19 particles from the air—the first such evidence in a real-world setting. Researchers noted the HEPA filters also removed detectable amounts of other pathogens that cause infections in hospitals, such as Staphylococcus aureus, Escherichia coli and Streptococcus pyogenes—a surprising finding because these pathogens are not typically considered to be airborne.