Virus Killing Light: Questions to Consider When Sorting Through All the Claims

Shortly after the COVID-19 virus began spreading rapidly in the United States in early 2020, healthcare workers, manufacturers, and researchers shifted their attention to the new demands brought on by this new, frightening pathogen encircling the globe. Many sought surface disinfecting solutions, while researchers sought to better understand the airborne nature of this virus’s transmission, and how effective masks would be at minimizing transmission. Manufacturers were ramping up production of N95 masks and other personal protective equipment, as national stockpiles were being drawn down. Disinfecting wipes and hand sanitizer were immediately in short supply, leading some manufacturers and researchers to point to the potential of using ultraviolet emissions as a way to inactivate the virus on surfaces and on masks.

As the year wore on, during trips to big box stores, and especially while browsing online retailers, consumers were presented with an increasing number of germicidal ultraviolet (GUV) products, with manufacturers touting their ability to kill pathogens using ultraviolet or visible light. The fact that these types of products are broadly available may give consumers a sense of confidence, but it may be a false one, created by a lack of standards that enable consumers and end users to compare product performance and make informed decisions. Great caution is warranted before money is wasted, or more seriously, injury to eyes and skin occurs. The claims are too numerous to address here, but in this article we identify a few GUV basics, while pointing to other useful resources.


In this article, GUV specifically refers to the use of short-wave ultraviolet emissions, known as UV-C, for the purpose of inactivating pathogens including bacteria, mold spores, fungi, and viruses. Ultraviolet wavelengths are segmented into UV-A (315 to 400 nm), UV-B (280 to 315 nm), UV-C (200 to 280 nm), and vacuum UV (100-200 nm). Adjacent to the ultraviolet region are the wavelengths that stimulate human vision, the visible light region, approximately 380 to 780 nm. There is some potential for using the violet portion of the visible light region for disinfection, although it is very minimal compared to UV-C. Daylight has been providing disinfection the longest of any source; however, the earliest use of electric GUV for disinfection purposes dates back nearly a century to the 1930s using low-pressure mercury lamps.

Today, low-pressure mercury lamps are still the most commonly deployed UV-C sources. These lamps resemble familiar fluorescent lamps, but without the phosphor coating that shifts the lamp’s UV discharge to visible light. Without this coating, and with specialized quartz glass, low pressure mercury lamps are the most efficient UV-C source commonly available today in terms of UV output. Solid-state ultraviolet sources (i.e., UV LEDs) exist and the technology is improving, but it remains to be seen if the technology can compete with the cost and performance of low-pressure mercury lamps.

Applying GUV is not as simple as replacing fluorescent lamps with low-pressure mercury lamps. Just as effective lighting design for the visual needs of occupants requires an understanding of the spectrum and amount of light hitting a surface over a given period of time, the effectiveness of germicidal ultraviolet is proportional to the wavelengths employed and the exposure dose: the product of the source output, the area irradiated, and time (typically in mJ/cm2, or J/m2). Without the right region of the electromagnetic spectrum, aimed at the target, for a sufficient period of time and at the right intensity, many GUV products can be a waste of money at best, but worse, can create a false sense of confidence that can be accompanied by a relaxation in mechanical cleaning efforts and overall caution.



Germicidal ultraviolet, used incorrectly, can result in eye and skin injuries that could increase long-term cancer risk. The safety issues with GUV can be minimized by using it in ways that avoid exposure to people and pets. GUV can be permanently integrated into mechanical ductwork to inactivate airborne pathogens, out of sight from building occupants. Likewise, GUV can be employed within plumbing systems to address waterborne pathogens. It is also used in upper room air disinfection, treating the air at 7 feet above the finished floor and higher, with ceiling fans used to circulate room air through the beam. GUV can also be integrated into portable devices for surface disinfection in settings such as patient rooms, where it can be placed in the room when unoccupied and left for a period of time to inactivate surface pathogens that are within line of sight of these portable units. Importantly, pathogens located in the shadows are not inactivated.

These uses of GUV require careful maintenance and attention. It is easy for an out of sight, out of mind mentality to lead to failed GUV lamps in HVAC ductwork that go unnoticed, or that nobody knows even exist. Additionally, safety sensors and timers are not always reliable. In the home, the presence of children and pets may not be detected by sensors, thus regardless of the commercial or residential space, it is important to implement protocols that will prevent people or pets from walking into spaces while they are actively being treated with GUV.

Another reason for caution regarding the use of GUV products is the lack of standard testing procedures, particularly important for understanding product output in terms of intensity and spectrum. There are presently no industry standardized methods of measurement to characterize the performance of GUV products. Manufacturers of these products employ their own largely proprietary methods for determining product performance, which makes comparisons between products very challenging, especially when comparing products between multiple manufacturers. Additionally, the presence of a safety label (e.g., UL) does not mean that the product has been tested for anything more than electrical safety.

Fortunately, help is on the way. Experts with a wide-range of backgrounds are working with the Illuminating Engineering Society ( and the International Ultraviolet Association ( to publish the first-ever industry standardized methods of measurement to instruct laboratories on how to take accurate and repeatable measurements of ultraviolet radiation. The first of these American National Standards (i.e., ANSI standards) to be published by the IES and IUVA will be methods of measurement for the sources themselves, including arc discharge sources like low-pressure mercury lamps, and solid-state sources such as UV LEDs.

These methods will enable laboratories to accurately and repeatably test UV sources to enable manufacturers to publish accurate, comparable performance data about the light sources used in upper room air disinfection systems, in duct work, and in mobile surface disinfection units. These ANSI/IES/IUVA standards will be issued later this year.

If you are looking for examples of the successful implementation of GUV, upper room air disinfection for combatting tuberculosis is currently the most well-documented application of GUV. In 2009, the National Institute for Occupational Safety and Health published a report summarizing much of this work and providing guidelines for upper-room ultraviolet radiation for tuberculosis. Another useful resource was published by the Illuminating Engineering Society in 2020: IES Committee Report 2-20-V1, Germicidal Ultraviolet (GUV) – Frequently Asked Questions. Researchers are continuing to learn more about the COVID-19 virus, and hopefully soon, new knowledge will provide more opportunities to inactivate this virus safely, efficiently, and effectively with germicidal ultraviolet.

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