What is ultraviolet (UV) light?
Ultarviolet (UV) light is a type of light that is similar to visible light but with different wavelengths, which makes it invisible to the human eye. UV light is usually divided into three categories, UVA, UVB and UVC, according to its wavelength.
How does ultraviolet light work?
UV light has been used for many years to sanitize locations such as hospital rooms and medical equipment. UV sanitization uses UVC light, which can remove viruses and bacteria by damaging their genetic material, DNA or RNA.
What's the difference between conventional UVC light and far-UVC light?
Conventional germicidal UVC light usually has a wavelength of around 254 nanometers and is very efficient at killing viruses and bacteria.However,this type of UV light can penetrate into our eyes and into our skin, so if people are directly exposed to conventional germicidal UV light over long periods of time they may be at risk for eye damage and potentially skin damage. As a result, conventional UVC light can't be used where people could be directly exposed to the UV light.
Far-UVC light has a shorter wavelength, usually around 222 nanometers. Far-UVC light also efficiently kills viruses and bacteria, but all available evidence shows that it is potentially safe for human exposure. This means that far-UVC lights, shining from above, can potentially be used to kill airborne viruses - including coronaviruses - in public places and when people are present.
How do we know that far-UVC light kills human coronaviruses and particular the coronavirus that causes COVID-19?
Columbia scientists were the first to show that far-UV light efficiently kills human coronaviruses:
In more recent ongoing studies, Columbia scientists have clearly shown that far-UVC light efficiently kills the SARS-CoV-2 coronavirus that causes COVID-19. These ongoing studies have not yet been published.
How do we konw that far-UVC light is safe?
Far-UVC light can penetrate only a very short distance in biological material. It can't penetrate the layer of dead cells on the surface of our skin, nor the tear layer covering the surface of our eyes, so it can't reach any living cells in the human body.
A number of different research groups, including at Columbia University, have performed extensive safety studies with far-UVC light and human skin, mouse skin, and mouse syes, and all evidence suggesting that far-UVC light has no harmful effects. Examples are:
Columbia studies on far-UVC safety in human and mouse skin:https://pubmed.ncbi.nlm.nih.gov/28225654/
Japanese studies on far-UVC safety in mice:https://pubmed.ncbi.nlm.nih.gov/32222977/
UK study on far-UVC safety in human skin:https://pubmed.ncbi.nlm.nih.gov/32452563/
Are there regulations concerning the safe use of UV and far-UVC light?
National and international safety regulations limit how much UV light can be used in public locations. These UV limits, established by the American conference of Governmental Industrial Hygienists and the International Commission on Non-Ionizing Radiation Protection, have been in place for more than 20 years. Far-UVC lamps are required to conform with these existing safety regulations.
How and where do you anticipate far-UVC light being used in the future?
As the COVID-19 crisis slowly off,there will be many situations where people are moving closer together in indoor spaces: Hospitals, buses, planes, trains, train stations, schools, restaurants, offices, theaters, gyms-to name but a few. In all these situations it would be beneficial to have overhead far-UVC lights that are continuously killing microbes, including the COVID-10 virus-and so limiting the spread of the virus from one person to another.
Can far-UVC light prevent the spread of other viruses such as influenza and measles?
Yes, in addition to COVID-19, far-UVC light is expected to be effective in reducing the spread of all viruses including influenza, measles, as well as the next potential pandemic virus.
Are far-UVC lights currently available? Can you recommend a manufacturer?
There are several manufacturers of far-UVC lamps and their fixtures and they are rapidly building up their capacity. However, Columbia University cannot recommend particular brands or manufacturers.
Will far-UVC light eliminate the need for social distancing, face masks or hand-washing?
All of there strategies help reduce the spread of COVID-19, but none are completely effective on their own. Together with all these existing techniques,far-UVC light has the potential to be a new and powerful tool to limit the spread of COVID-19 and other infectious diseases.