A new study from Columbia University Irving Medical Center has found that more than 99.9% of coronaviruses present in airborne droplets were destroyed using a particular wavelength of ultraviolet (UV) light, which is safe to use around humans.

Lead author David Brenner said, “Based on our results, continuous airborne disinfection with far-UVC light at the current regulatory limit could greatly reduce the level of airborne virus in indoor environments occupied by people.”

The study was published Wednesday in Scientific Reports.

Experts say that conventional germicidal UVC light (254 nm wavelength) could disinfect unoccupied spaces, such as empty hospital rooms or empty subway cars; however, direct exposure to conventional UV lamps could be a health hazard.

The researchers have been investigating far-UV light (222 nm wavelength) to continuously and safely disinfect indoor areas. They said far-UV light cannot penetrate the outer layer of the skin and the eye so it cannot damage livings cells in the body.

They found that the far-UV lamp was able to kill seasonal coronaviruses that are structurally similar to the new coronavirus (SARS-CoV-2), which causes COVID-19 infection.

The study found that more than 99.9% of the exposed viruses were killed by very low exposure to far-UV light.

Considering their findings, the authors estimate that continuous exposure to far-UV light would kill:

  • 90% of airborne viruses in about 8 minutes
  • 95% in about 11 minutes
  • 99% in about 16 minutes
  • 99.9% in about 25 minutes

As far as human safety is concerned, far-UV light may be feasible and safe to use in occupied indoor public places in order to reduce the risk of human-to-human transmission of coronaviruses.

Brenner said, “Far-UVC light doesn’t really discriminate between coronavirus types, so we expected that it would kill SARS-CoV-2 in just the same way. Since SARS-CoV-2 is largely spread via droplets and aerosols that are coughed and sneezed into the air it’s important to have a tool that can safely inactivate the virus while it’s in the air, particularly while people are around.” “Because it’s safe to use in occupied spaces like hospitals, buses, planes, trains, train stations, schools, restaurants, offices, theaters, gyms, and anywhere that people gather indoors, far-UVC light could be used in combination with other measures, like wearing face masks and washing hands, to limit the transmission of SARS-CoV-2 and other viruses,” Brenner added.