ANALYSIS AND OPINION UV ILLUMINATION


Scrutinising craze for UV Covid-19 disinfection


With increased interest in using UV light to deactivate viruses, Robert Yeo, director at Pro-Lite Technology, discusses the safety and effectiveness of UVC devices


U


ltraviolet (UV) radiation has been in the media a lot recently. As life


slowly starts returning to normal (or as normal as possible) and we start venturing out more following the coronavirus lock-down, our attention turns to how we can minimise the risk of acquiring the virus ourselves, or of transferring it to others, particularly the more vulnerable members of society. Governments were clear from the outset that we should wash our hands thoroughly after contact with a potentially infected surface.


Then, on 23 April, President


Donald Trump speculated during a White House coronavirus task force briefing that disinfectants and UV light were possible treatments for the virus. It is indeed the case that exposing your insides to UVC light will probably prevent you from falling victim to the virus, but that’s because the carcinogenic radiation will do you first. As of 30 April, a New York


Times article, titled ‘Trump’s disinfectant talk trips up sites’ vows against misinformation’, reported that there were 780 Facebook groups, 290 Facebook pages, nine Instagram accounts and thousands of tweets promoting UV light therapies that were posted after Trump’s comments. This is in addition to more than 5,000 other social media posts promoting


6 Electro Optics June 2020


disinfectants as a virus cure. As an example of businesses seeking opportunities in UV light therapies, one Colorado-based firm was quoted on 30 April by Bloomberg as promoting the use of UV LED light that it claims could be delivered into the lungs by means of a catheter inserted into the throat (article title: ‘Colorado firm sees opportunity in trump’s criticized UV idea’). However, the consensus from the medical community is that this technique is still at the research stage and as yet of unproven clinical efficacy. Each new day brings ever


more messages into my email inbox from firms offering me deals on UV LED light ‘wands’, devices which are being promoted as a means of sterilising surfaces and killing viruses. As to their effectiveness and safety, well that’s the subject of this article. Mr Trump has certainly managed to raise the public’s awareness of UV radiation. My aim is to balance the discussion with some science and facts.


Measuring UVC radiation Scientists believe that UVC radiation may ‘deactivate’ the Sars-Cov-2 virus that is responsible for the Covid-19 respiratory disease. Although this thesis has yet to be proven, tests performed on related coronaviruses, including the Sars coronavirus, have revealed


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that UVC germicidal radiation is effective as a means of deactivating these viruses. In general, germicidal UV radiation is understood to damage (mutate) the RNA and DNA nucleic acids in a virus, which prevents replication, leading to its deactivation. A key metric in the


effectiveness of the UVC radiation is the ‘dose’ delivered. Dose is the product of a lamp’s irradiance and the cumulative exposure time. Irradiance is


“Each new day brings ever more messages into my email inbox from firms offering me deals on UV LED light ‘wands’”


the total light (radiant flux) received at a surface per unit area of the surface exposed. It is expressed in units of Watts per square metre (W/m2


product of irradiance and time (in seconds) and is expressed in units of Joules per square metre (J/m2


).


Covid-19 is understood to be spread by coming into direct contact with respiratory droplets, or by transfer from an infected surface via a person’s hands to their mouth, nose or eyes. The extent to which the


Covid-19 virus is spread via airborne transmission is not fully understood, but scientists think that airborne transmission is a real danger. Germicidal UV lamps are therefore being proposed both to irradiate contaminated surfaces and to irradiate the air in a room. While UVC radiation is of


). Dose is the


proven utility in terms of its effect on viruses and bacteria, exposure to the human skin and eyes must be avoided. Notwithstanding the recent ill- informed speculation by certain politicians on the use of UV light on (or indeed within) the human body as a possible treatment for Covid-19, UVC is known to have a very harmful photobiological effect. Specifically, the use of UVC germicidal radiation for hand sanitisation is strongly discouraged. Also note that neither UVB (280-315nm) nor UVA radiation (315-400nm) provides for any significant germicidal disinfection. UVC lamps should be operated in strictly controlled environments, often within light-tight enclosures, to avoid the possibility of exposure to our skin or eyes. As with all sources of artificial optical radiation, UVC germicidal lamps must comply with the risk group labelling and


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