The basics of COVID-19

By now, almost everyone in the world knows the basics of COVID-19 and there are ample resources for more information. Over the last year, we’ve learned that COVID-19 is primarily transmitted through the air in enclosed environments. In addition to the basics of sanitation, social distancing, and mask-wearing, UV light in the germicidal range can inactivate COVID-19.

 How Does UV Light Disinfect?

Ultraviolet light has been used for decades for surface and air disinfection for its proven ability to retard bacterial growth and inactivate viruses such as Coronavirus.

The best way to explain how UV-C inactivates COVID is this - the wavelengths of light break down the outer “shell” of the virus breaking down the interior of the virus and not allowing it to replicate. If you’re so inclined, there’s a good summary video on this from Physics World here:

Where the confusion has abounded is the in the types of UV light there are as well as cheap consumer goods that provide little to know disinfection due to inadequate power and poor dosing.

Not All Ultraviolet light is Created Equal

Within the ultraviolet spectrum, there are three subspectra known as UV-A, UV-B, and UV-C. Each of these operates within its own spectral range. Over decades of study, UV-A and UV-B have been shown to retard bacteria growth and are generally safe for direct exposure to people. However, UV-A and UV-B emitting devices will not inactivate the Coronavirus or any virus.

Short-Wave UV-C is the only portion of the spectrum proven to inactivate Coronavirus, but there are Safety considerations

UV-C is effective for fighting the Coronavirus, but there are important safety considerations to make in its deployment. Direct exposure of UV-C to the eyes can cause nasty irritation and temporary blindness (similar to looking directly into the sun). UV-C shined directly on human skin will cause a sunburn-like irritation if skin is exposed over time. We’ll discuss how to avoid this more in our methods section.

A Note About Dosing

Academic research, as well as marketing materials from different manufacturers, often refers to “dosing” this refers to the specific wavelength of UV-C their device is using and how long that wavelength must be energized to inactivate the Coronavirus. Reputable UV-C manufacturers will have recommended dosing as part of their product literature.

When it comes to specific applications, dosing models can be applied through computer programs to provide guidance on how many fixtures, filters, etc should be used in a given space. A good rule of thumb:

17 mW of 254-nm lamp-emission radiant power per cubic meter (m3) of space to disinfect air.

This measurement is taken from the IES report linked to above.