(Issue: February 2021)

Germicidal Lighting

By Craig DiLouie, CLCP, LC


The COVID-19 pandemic has sparked significant interest in applying germicidal ultraviolet (GUV) lamps to buildings as a layer of disinfection supporting other methods such as managing traffic flow and cleaning. This spells opportunity for lighting management companies but also the need for caution due to the risks inherent in GUV technology. 

For decades, GUV lamps have been used to disinfect viruses and bacteria on surfaces, in manufacturing of certain products, and in water and wastewater treatment. While called “lamps,” with the category sometimes referred to as “germicidal lighting,” these sources do not provide useful visible illumination. They are instead emitters of energy in the ultraviolet portion of the electromagnetic spectrum that neutralize bacteria and viruses, including potentially SARS-CoV-2, the coronavirus that causes the disease known as COVID-19. 

UV is categorized as A, B, or C according to wavelength, offering different germicidal effects and risks based on dosage, which in turn depends on intensity (wavelength, proximity, power) and duration of exposure. The higher the intensity, the shorter amount of time required to neutralize pathogens. 

UV-A (315-400 nm) is typically used in products such as tanning beds, though it can have a germicidal effect at certain dosages. UV-B (280-315 nm) can have a germicidal effect at certain dosages as well, though it can be harmful to people and animals at high dosages. Bordering UV-A is a violet visible light band (400-405 nm) that has been demonstrated to be effective against certain bacteria and mold. 

UV-C (180-280 nm, typically applied at 254-255 nm) has been shown to be effective against viruses and bacteria, including SARS-CoV-2, making it preferrable for GUV applications. UV-C is generally hazardous to humans and animals while also degrading organic materials, however, creating a challenge in how to apply it to buildings. Threshold limits for repeated human exposure to UV are expressed in IEC 62471, Photobiological Safety of Lamps and Lamp Systems. 

In the past, UV-C was typically limited to specialized applications. The COVID-19 pandemic has stimulated the development of new approaches. As UV-C is a line-of-sight source, achieving true whole-room disinfection is often impractical, but it does make the emission controllable. Approaches vary in what portion of the room is disinfected, what pathogens are neutralized, whether the pathogens are neutralized in the air or on surfaces or both, and how long neutralization takes. Low- and high-pressure mercury lamps, excimer lamps, and LEDs are used for GUV applications, with LEDs now in rapid development.  

Room air disinfection: A device with an integral fan draws air past concealed GUV lamps. The device may mount on the wall. The device theoretically produces whole-room air disinfection, though it doesn’t disinfect surfaces. 

Upper-air disinfection: GUV lamps are installed in a wall-mounted emitter or integrated into indirect-direct luminaires providing separately controlled up/down visible light and upward GUV emission. The luminaire may be controlled so that the GUV emits only at certain times, until a certain dosage is achieved, or during unoccupancy. This approach requires sufficient ceiling height and air exchanges. 

Whole-room disinfection: Direct GUV devices are installed that disinfect air and surfaces. Note that “whole room” is again typically not entirely accurate, as GUV is dependent on line of sight. Several approaches may be used, some extraordinary in their novelty. 

One is to deploy direct GUV devices that operate only when the space is unoccupied, such as a hospital operating room. In other buildings, a GUV system could be operated overnight in a strategy called passive GUV disinfection. Larger applications might be cost-effectively served with a mobile robot. 

GE Current took another approach, which was to develop a direct GUV device that is designed to operate within safety limits by reducing intensity. The company’s 365DisInFx UV-C luminaire is a puck-shaped device that mounts on the ceiling for coverage of up to 50 sq.ft. at a 10-ft. mounting height. The tradeoff is amount of time required to neutralize pathogens—up to three hours for the large majority and six hours for nearly all of the remainder, according to the company. 

And another approach was commercialized by Ushio, which developed a 222-nm excimer (“Care222”) lamp that filters out harmful, longer UV wavelengths. Acuity Brands acquired the lamp for integration with select LED luminaires among three of its brands. The combination of the wavelength and controlled pulsing of the separately controlled GUV output is designed to enable operation within safety limits. According to a Columbia University study, the GUV component can neutralize the majority of airborne pathogens in about eight minutes and the rest in about 25 minutes. 

The right approach depends on the customer’s disinfection goals, application characteristics, and risk tolerance. Questions such as what pathogens need to be neutralized, where, and how quickly need to be answered. 

When evaluating product, lighting management companies should seek trusted brands, as the technology is still developing. They should request evidence that supports disinfection and safety claims, look for safeguards that protect users and maintenance personnel, examine what maintenance is required to ensure safe ongoing operation, and evaluate the product carefully, including any controls. Being able to do all this effectively requires education and caution, as faulty or poorly designed products, misapplication, and installation error pose significant risks. 

The pandemic is having a significant impact on American society. Even after it ends, many mitigation measures may become permanent, including GUV devices. Lighting management companies may benefit by getting to know the technology. 

Craig DiLouie, CLCP, LC, principal of ZING Communications, Inc., is a consultant, analyst and reporter specializing in the lighting and electrical industries, and a regular contributor to LM&M. You may contact Craig at cdilouie@zinginc.com.