A Beam of Sanitizing Light: Disinfection with filtered far-UV-C

By Craig DiLouie | Dec 15, 2020
Germicidal UV lamp glowing blue-green | Shutterstock / Nor Gal




The COVID-19 pandemic is driving interest in broader applications of germicidal ultraviolet (GUV) lamps to disinfect building spaces. The challenge with GUV is that it is harmful to human health as well as viruses and bacteria, which limits its application in occupied spaces. However, a portion of the UV spectrum—within recommended limits—is effective against pathogens while posing a minimal risk to humans, which offers potential for disinfection in occupied spaces. This technology, pioneered by Columbia University, New York, and commercialized by Ushio Inc., Tokyo, is poised to enter the North American lighting market through Atlanta-based Acuity Brands.

Used for decades as a disinfection method, ultraviolet light is categorized as A, B or C according to spectral position, each with differing effects and risks. UV-A, with wavelengths of 315–400 nanometers (nm), is used in insect traps, tanning beds, etc., but is not powerful enough to inactivate viruses. UV-B (280–315 nm) can be if the dosage is strong enough, but it can be harmful to humans. UV-C (200–280 nm) will inactivate viruses and bacteria, but exposure is hazardous to humans. As a result, UV-C is preferred for GUV, but it is typically applied in unoccupied spaces.

Researchers at Columbia University Irving Medical Center investigated far-UV-C (222 nm, compared to 254 nm in conventional GUV) and found it to be effective against influenza and seasonal coronaviruses present in airborne droplets. They estimated that continuous exposure at the current regulatory limit would kill 90% of airborne viruses in about eight minutes, 95% in about 11 minutes, 99% in about 16 minutes and 99.9% in about 25 minutes.

Finally, they determined that filtered far-UV-C does not penetrate the eye’s tear layer or the skin’s outer, dead-cell layer, and therefore cannot reach or damage living cells in the body when used within recommended limits.

In September 2020, a group of researchers at Hiroshima University Hospital and Hiroshima University in Japan published a study demonstrating that filtered far-UV-C radiation effectively reduced SARS-CoV-2—the virus that causes COVID-19—by at least 99.7% in an in-vitro experiment.

“Our results suggest that this technology could be used for infection prevention and control against COVID-19, not only in unoccupied spaces, but also occupied spaces,” the researchers concluded.

The study, however, did not investigate real-world effectiveness. The researchers called for further study. Nonetheless, the results suggest filtered far-UV-C offers the potential for use as a disinfection strategy in occupied spaces.

Manufacturer Ushio used the technology to develop a line of 222-nm far-UV-C excimer lamps. Called the Care222 series, these instant-start, mercury-free lamps are available in a 12W module or a 20W or 300W lamp. The module features a patented filter that eliminates the hazardous longer wavelengths above 230 nm.

In June 2020, Acuity Brands acquired exclusive rights from Ushio to buy the filtered far-UV-C module for use in North America. The manufacturer incorporated it into a range of ceiling- and wall-mounted luminaires for launch in late 2020 from its Mark Architectural Lighting, Lithonia Lighting and Healthcare Lighting brands.

“When applied correctly, this solution provides high-quality illumination and continually reduces pathogens while meeting safety guidelines for occupants within the space,” said Gary Trott, Acuity’s vice president of technology commercialization.

Trott said ideal applications include those spaces with high levels of social interaction, such as offices, meeting spaces, classrooms, public restrooms, restaurants/hospitality, performing arts and sports venues, public transit, retail, health clubs and certain healthcare settings. An algorithm pulses the filtered 222-nm light to enact continual dosing within exposure limits established by the American Conference of Governmental Industrial Hygienists, Cincinnati. As effectiveness is based upon line of sight, its use is recommended as part of a multibarrier approach that includes regular cleaning.

The layout and number of modules required for these luminaires is specifically calculated for effectiveness of disinfection and illumination using the company’s Visual Lighting software. Luminaires arrive on a job site factory-calibrated per these calculations and specifications and should be installed according to the design with all appropriate parameters verified in the field through functional testing.

Trott believes these luminaires will be popular as more organizations shift to a permanent pathogen mitigation stance.

About The Author

DiLouie, L.C. is a journalist and educator specializing in the lighting industry. Learn more at and

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