Illuminating Engineering Society

Germicidal UV (GUV) refers to using ultraviolet radiant energy to inactivate bacteria, mold spores, fungi or viruses. When the process is applied in a given location, it has generally been referred to as ultraviolet germicidal irradiation (UVGI). Because of the public’s concern about ionizing radiation (e.g., X-rays and gamma rays), the term GUV avoids needless concerns about a link with that type of radiation. Another non-technical term is germicidal light, although “light” is technically only visible radiation.

No. Germicidal ultraviolet (GUV) – refers to short-wavelength ultraviolet “light” (radiant energy) that has been shown to kill bacteria and spores and to inactivate viruses. Wavelengths in the photobiological ultraviolet spectral band known as the “UV-C,” from 200 to 280 nanometers (nm), have been shown to be the most effective for disinfection, although longer, less energetic UV can also disinfect if applied in much greater doses. UV-C wavelengths comprise photons (particles of light) that are the most energetic in the optical spectrum (comprising UV, visible, and infrared) and therefore are the most photochemically active. 

Yes, UV-C kills living bacteria, but viruses are technically not living organisms; thus, we should correctly say “inactivate viruses.” Individual, energetic UV-C photons photochemically interact with the RNA and DNA molecules in a virus or bacterium to render these microbes non-infectious. This all happens on the microscopic level. Viruses are less than one micrometer (µm, one-millionth of a meter) in size, and bacteria are typically 0.5 to 5 µm.

Yes, if the virus is directly illuminated by UV-C at the effective dose level. UV-C can play an effective role with other methods of disinfection, but it is essential that individuals be protected to prevent UV hazards to the eyes and skin as elaborated in Section 4. UV-C should not be used to disinfect the hands!

No. UV-A and longer (visible) wavelengths do not have germicidally effective emission wavelengths to inactivate viruses. Their relative disinfection capability is very minimal on the order of 1,000 times less effective in terms of fluence rate than the low-pressure mercury germicidal lamp. There have been only very special applications of wavelengths in the UV-A and violet (e.g., 405 nm), which require very high doses not practical in an occupied environment and were not recommended for viral sterilization. The trace amount of UV-B that is emitted from some white-light fluorescent lamps probably has similar efficacy.

Light-emitting diodes (LEDs) have been available for some time in the UV-A region. The advantage of UV-A or visible-light LEDs would be that they can easily be incorporated into LED-based luminaires, and there might be no need for protective gear. However, the efficacy of violet or UV-A energy that is not harmful to the skin or eyes is minimal.

UV-B (280 to 315 nm), particularly the shorter wavelengths near 300 nm and below, can be relatively effective as a germicidal source, but in accidental exposures there is a significantly higher risk for severe sunburn and even delayed effects for both skin and eyes, because UV-B penetrates the skin more deeply.

Yes, particularly in the late spring and early summer when the sun is high in the sky and the UV index is high. At a UV Index of 10, the duration to achieve at least a three-log kill of bacteria (99.9% killed) is estimated as less than one hour.[5]

[5] Lytle CD, Sagripanti J-L. Predicted inactivation of viruses of relevance to biodefense by solar radiation. J Virol. 2005;79(22):14244-52.