The novel coronavirus pandemic has sparked fresh interest in germicidal ultraviolet lamps (GUV) for disinfection. For some 40 years, GUV have been used to disinfect potable water and wastewater, certain products such as contact lenses, and surfaces against a wide range of bacteria and viruses. On its website, the International Ultraviolet Association makes a case that UV disinfection can play a role in a multibarrier approach to reducing transmission of SARS-CoV-2, the virus causing COVID-19. This may lead to increased applications for GUV in buildings, but there are risks.

“It’s potentially good and bad,” said Mark Lien, industry relations manager, the Illuminating Engineering Society (IES). “The pandemic has demanded solutions for situations previously unencountered. Using upper-air GUV disinfection could potentially save the lives of our front-line medical workers. There is also a potential for users to misapply these products, resulting in health and safety concerns. Using GUV properly requires learning about the technology.”

In April 2020, the IES released a free guide to GUV disinfection and its potential to safely reduce transmission of SARS-CoV-2 (https://bit.ly/2xDY7UI). Produced by the IES Photobiology Committee, the report provides answers to FAQs, drawing from expertise from the Centers for Disease Control and Prevention, the Food and Drug Administration, Harvard Medical School, the Icahn School of Medicine at Mount Sinai Medical Center, and manufacturers and research organizations.

Not all UV is equal

GUV emission is in the UV-C band of wavelengths on the electromagnetic spectrum (200-280 nanometers). UV-C radiation can kill bacteria and render viruses inactive, including SARS-CoV-2 in line of sight and at the right dosage. Longer-wavelength, lower-energy UV-B (280-315 nm) can disinfect if applied in much greater doses. UV-A (315-400 nm), used in insect traps and tanning beds, etc., is not powerful enough to be effective against viruses. Visible light disinfection (400-405 nm) produced by LED luminaires promoted by such companies as Kenall (Indigo-Clean) and Vital-Vio Inc. can be effective at killing bacteria and mold but not for inactivating viruses. As an aside, direct sunlight is not proven effective against SARS-CoV-2.

Traditionally, GUV is used to directly disinfect surfaces in unoccupied, critical applications, such as manufacturing, water treatment and healthcare facilities, where it may be used in operating rooms. The challenge with UV-C is that it is hazardous to health and safety; exposure can increase cancer risk, and even short exposures can produce burns on unprotected skin and retinal damage. It also degrades organic materials. High dosages of UV-B can also be harmful.

As a result, expanding application of UV-C is challenging, particularly for whole-room disinfection and even more particularly for occupied spaces, given the protective gear that would be required for occupants during UV-C emission. One solution is to install GUV in air handlers, which can be effective with certain aerosolized germs but must be properly designed and maintained. The most effective GUV application, according to IES, is upper-room disinfection. In this scenario, ventilation circulates air toward the ceiling, where it is treated in the space. This requires proper design to international standards and sufficient air exchanges and ceiling height.

“GUV is a targeted solution to be used only in spaces where disinfection is necessary,” Lien said.

Because it’s a line-of-sight technology unable to work around objects, UV-C should be considered only one part of a multibarrier approach, including methods such as periodic cleaning.

“It seems likely that UV-C applications will be touted for buildings in the near term and over the next five years or so,” said Mark S. Rea, Ph.D., professor, Lighting Research Center, Rensselaer Polytechnic Institute. “However, UV-C has limited use in occupied rooms. Restrooms with motion sensors to ensure vacancy might become a common method, but I doubt we will be sending UV-C robots into schools and offices. Other UV-A and blue light—405 nm—technologies, while of unknown effectiveness on viruses, can be applied in occupied spaces to destroy harmful bacteria.”

One interesting technology being pioneered by organizations such as Columbia University is excimer, low-discharge lamps that produce a 222 nm emission, which can deactivate viruses while not causing skin and eye damage. These lamps theoretically could support disinfection of occupied spaces in combination with other disinfecting approaches, but the technology is relatively new. Currently, LEDs—again, theoretically—can generate an emission around 222 nm, but they can’t achieve the same light output.

Due to the coronavirus pandemic, GUV is likely to continue to develop in technology and application. Contractors responding to interest in GUV should become informed, stay safe and work only with trusted manufacturers that provide proper safety cautions and instructions.