Hide table of contents

Roko Mijic, Alexey Turchin

Epistemic status: Many different uncertainties here, but the idea has some good evidence in favor of it and a high potential payoff.

Tl;dr: We should urgently investigate putting special human-safe Far-UVC lamps all over our built environment to ‘kill’ virus particles whilst they are in the air, thereby vastly reducing covid-19 spread.

Inspired by: https://www.nature.com/articles/s41598-018-21058-w

One of the most promising and neglected ideas for combating the spread of covid-19 is the use of ubiquitous ultraviolet light in our built environment (trains, offices, hospitals, etc). Ultraviolet light is already being used as a disinfecting agent across the world; it goes by the acronym UVGI - “Ultraviolet germicidal irradiation”. The energetic photons of UVC light break chemical bonds in DNA and kill/inactivate both viruses and bacteria.

Ultraviolet light on earth exists on a spectrum between 200nm and 400nm. Light above 400nm is blue visible light. Light below 200nm is called “vacuum UV” because it is strongly absorbed by the oxygen in ordinary air and therefore cannot exist except in a vacuum or some other non-air medium. Within the 200-400nm range we have UVA, UVB and UVC, and at the short-wave edge of the UVC band we have “Far-UVC”, from roughly 200nm–220 nm.

Safety considerations

Human beings are also vulnerable to UV radiation. It causes skin cancer and serious eye damage.

However, recent research suggests that the Far-UVC band is actually safe for human skin because it cannot penetrate through the thin layer of dead skin cells on the surface of our skin.

This means that it might be possible to mount a long-term response to covid and other pathogens by constantly illuminating our built environment with light from specifically the Far-UVC band. If the Far-UVC light is indeed safe for humans, the Far-UVC could be on at all times and could destroy or deactivate viral particles before they can spread from person to person.

Why hasn’t this already been considered by relevant authorities? Far-UVC appears in a literature review by WHO, but it is not currently being acted upon as the amount of evidence in favor of safety and efficacy is small.

There is some uncertainty about whether Ozone generation by this band (200nm-220nm) would be problematic. Ozone is not great for your health. However, it seems to be the case that the 200-220nm band is not a strong producer of Ozone. In addition, UV degradation of surfaces might result from chronic UV exposure.

Balancing harms of action and inaction

Even if Far-UVC is somewhat harmful it might still be a good idea to implement. Small harms from Far-UVC light might be much less bad than large harms from covid-19, or from the economic damage caused by the lockdown which one author estimates to be roughly $10 million per minute, plus much personal hardship which will be caused by the forthcoming recession.

Furthermore, UV light is easier to defend a person against than a virus. Sun-creams, clothing and eyewear that defend against UVC may be less bad than a semi-permanent lockdown or an exponentially growing covid-19 outbreak that results in millions or tens of millions of deaths. UV in the built environment could even be managed intelligently - computer vision could identify where the people were and turn on UV lights only in unoccupied areas, though such a project would at best be ready by the start of 2021 (and then only with wartime levels of effort and purpose).

If the safety claims of Far-UVC are partially true rather than fully true, a combination of using Far-UVC with physical protection like eyewear may still cause only acceptable losses to cancer and eye damage. In the longer term, such “almost safe” Far-UVC could be combined with intelligent management at various levels of granularity; imagine a lift that is bathed in Far-UVC every time people leave it, or “walls” of Far-UVC separating people that automatically turn off momentarily when a person walks through them. The ultimate system might even adjust the power of the Far-UVC using AI.

Epidemiological considerations

Even an ideal Far-UVC solution that was harmless to humans, 100% lethal to covid-19 particles and easy to deploy at scale might not be sufficient to reduce R to exactly 0. But the key question is whether it could reduce R below 1 whilst also allowing most economic activity. An easy preliminary experiment to run would be to put virus samples in mouse cages - perhaps in aerosolized form - treat some cages with Far-UVC, leave other cages alone, see if infection rates go down in the treated cages.

This is an important source of uncertainty and further research is needed.

Scaleup considerations

Even a perfect system is useless if it cannot be scaled up and implemented across the globe. Far-UVC can be produced from Krypton Chloride (Kr-Cl) Excimer Lamps, but modern Aluminium Nitride (AlN) Far-UVC LEDs are a better solution for the long term. In the even longer term, collimated Far-UVC could be produced by lasers. This is an important source of uncertainty and further research and expert input is needed.

Power considerations:

The amount of Far-UVC energy required to kill 99% of the viral particles is estimated to be around 20J/m^2. With a power of, say 5W/m^2, a system would need 4 seconds to mostly sterilize a viral aerosol that could travel from person to person. However a lower power system would still have some benefits - we know that people can be infected by air that was contaminated 30 minutes earlier. Higher power in these wavelengths could be difficult to achieve with Kr-Cl Excimer Lamps as the overall efficiency from electricity to Far-UVC is ~10% (White's Handbook of Chlorination and Alternative Disinfectants, under figure 17.14). AlN Far-UVC LEDs would likely have a much higher conversion efficiency.


One of the greatest benefits of Far-UVC is that it would be a very general weapon against pathogens. Far-UVC kills/deactivates bacteria, viruses and other pathogens. MRSA, C-DIFF, influenza, etc are all killed by UVC, as is the next problematic pathogen, whatever it is.


There are many different reasons that Ubiquitous Far-UVC might not work out, but if it did work out it could have huge benefits. For this reason the authors believe that it should get more attention at this critical time. Scaleup and safety and efficacy trials must all be carried out as quickly as possible, preferably in parallel. More importantly, the idea needs more attention from experts in the relevant fields - UV physics, epidemiology, and people who study the etiology of skin cancers. As of writing there are reports that the US government estimates the epidemic could last for 18 months, so a plan like Far-UVC that will take months to implement may still be a critical component of a response later this year.

Appendix. Other ways to use UV light to fight coronavirus

One of the explanations of the flu and other infections seasonality is that the Sun's UV kills viruses. However, people spend a lot of time indoors even during summer, and especially during self-isolation. Most of our infections are happening indoors: at home, in transport and in working places. UV from Sun could be part of the explanation of the lower instances of coronavirus in southern countries.

If we replace light bulbs everywhere with light sources which also emit UV light of some special wavelength, we will kill most of the airborne viruses and will clean fomites. Thus, we will create artificial summer everywhere and will lower R0 of coronavirus below 1.

The main obstacles are the duration of exposition and possible harm to people. Recently in Moscow 20 children had burns in their eyes after a school teacher forgot to turn off the UV cleaner in the classroom.

There are several other ideas, besides Far-UVC light, to prevent human eye and skin damage:

1) Intellectually controlled UV lighting. UV light source turns on the maximum level when there are no people in the room. We already have motion detectors for lighting, but here they will work in reverse. Light with motion detection could also direct light in directions, where there is no motion, so no people. On the video, one can see UV light sources on sale with motion detectors:

The power of light could be temporarily increased after the sound of sneezing. But it will make all the system more complex and its large-scale implementation will take longer time. If Krypton Chloride Excimer bulbs are used, their lifetime is not great, so they can’t run constantly. But if we can get the Aluminium Nitride LEDS then lifetime and efficiency will be better.

2) Not “too strong” sources of UV, which are producing Sun’s intensity of UV and which act mostly on fomites. As we know, humans can survive at least 1 hour of sunlight UV exposure without strong damage (on beaches). We could use it as a reference point to calibrating UV sources.

3) Strong UV lighting + gloves. Everyone will wear gloves, masks and glasses outside. In that case, no skin will be exposed to the UV lighting (and to viruses). Wearing PPE will be effective anyway. Women in the East are wearing full cover clothes, and they are ok.

4) Wearable headlight UV will direct UV light in the opposite direction to the person’s eyes but will cover everything he inhales or touches, as well as his hands. The light will be strongest near the human face (but not affecting the face), and will attack droplets which the person is about to inhale. However, the light will dissipate in the distance of 1- 2 meters to safer levels. UV headlamps already exist and on sale, but may be not strong enough for disinfection. It will be especially effective if wearables Far UVC light sources will be used.

5) UV flashlight - Torch that emits UV radiation in a wide beam. Runs off main power. Could be used by cleaners as an additional step when cleaning surfaces.


  1. Simpler, easier, cheaper and faster to build than other solutions
  2. Less harm to people, as UV light can be directed, and is not always on
  3. Proving ground (an MVP, in startup terms) for more advanced implementations
  4. Mobile; could be used in multiple locations


  1. Less effective than always on UV lights and lamps
  2. Requires additional time/effort on top of normal cleaning routines

Artificial light exists currently almost everywhere, where contemporary humans live: in homes, in any shop, in cars and even on the streets. All we need is to replace electric lamps. Large amounts of lamps could be manufactured in 0.5-1 year, and smaller amounts for critical places like elevators in the even shorter notice.

However, there is a problem of actual testing the technology until it will be approved as safe and effective by the FDA. It is technically difficult to make deep UV (220nm) light-emitting diodes.

A good start will be to put UV lights in the places of short use: elevators, shops, restrooms.

It is much more convenient to wear protection against light than protection against viruses, and after a few months of lockdown, the idea of returning to almost normal life but with sun cream and/or gloves will be quite nice.


Welch, D., Buonanno, M., Grilj, V. et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep 8, 2752 (2018). https://doi.org/10.1038/s41598-018-21058-w

Narita K, Asano K, Morimoto Y, Igarashi T, Nakane A (2018) Chronic irradiation with 222- nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses. PLoS ONE 13(7): e0201259. https://doi.org/ 10.1371/journal.pone.0201259

Willie Taylor, Emily Camilleri, D. Levi Craft, George Korza, Maria Rocha Granados, Jaliyah Peterson, Renata Szczpaniak, Sandra K. Weller, Ralf Moeller, Thierry Douki, Wendy W.K. Mok, Peter Setlow DNA damage Kills Bacterial Spores and Cells Exposed to 222 nm UV Radiation Applied and Environmental Microbiology Feb 2020, AEM.03039-19; DOI: 10.1128/AEM.03039-19

Colorado company uses UV lighting technology to kill 99.9 percent of bacteria and viruses. Fox Denver, 7 Macrh 2020


Sorted by Click to highlight new comments since:

This seems well-researched and examined, and it may be neglected, important and even has some level of tractability. Given the timeliness of the topic, I'm quite surprised this is not much more upvoted; it feels like one of the better posts on the EA Forum I've seen. Thanks for writing!

In the BBC today: Coronavirus: Robots use light beams to zap hospital viruses


You don't mention this, and maybe there is no research on it, but do we expect there to be much opportunity for resistance effects, similar to what we see with antibiotics and the evolution of resistant strains?

For example, would the deployment of large amounts of far-ultraviolet lamps result in selection pressures on microbes to become resistant to them? I think it's not clear, since for example we don't seem to see lots of heat resistant microbes evolving (outside of places like thermal vents) even though we regularly use high heat to kill them.

And even if it did would it be worth the tradeoff? For example, I think even if we knew about the possibility of antibiotic resistance bacteria when penicillin was created, we would still have used penicillin extensively because it was able to cure so many diseases and increase human welfare, although we might have done it with greater care about protocols and their enforcement, so with hindsight maybe we would do something similar here with far-ultraviolet light if we used it.

I think that for viruses it will be difficult to become completely radiation resistant, as it would require complete overhaul of their makeup: thicker walls, stronger self-repair.

I like this idea. On the other hand, the other promising environmental measure analysed by WHO, ventilation, seems very straightforward and intuitive - but it's still neglected (I haven't observed any emphasis on that recently, at least). If people can't open their windows and turn off the air conditioning during epidemics, I wouldn't be very hopeful concerning UV lamps.

What are the chances that the virus will flow from the apartment beneath mine into the mine one during ventilation?

Epistemic status: not my expertise, I'm guessing.

It's hard for it to flow upwards, and it'll probably disperse a lot (since it doesn't reproduce outside a host, I guess this minimizes the chance of being infected)... but yeah, if your apartment is close to an infected person, there's a chance that the wind will carry virions to your apartment; that's why hospitals are supposed to place infected people according to the airflow.

There's probably a trade-off between probability of external contamination vs. time virions stay viable on surfaces in an environment. It seems like, at least for other respiratory infections, for most collective environments, we should be more concerned about the latter.

What's your opinion here? Of course, there's a point where the external environment becomes so contaminated (in a hospital, or if everyone in your building is infected) that you better insulate your personal environment as best as you can.

I heard about infection in HK via vent tubes.

If I were in a space with many people, I would like the windows will be open. At home, not.

I agree that preventing exposure to virions is a priority, but I am concerned with indoor air quality overall, especially if people are staying indoors for long periods: https://en.m.wikipedia.org/wiki/Indoor_air_quality?wprov=sfla1

Some internal air cleaner exist, including the ones with UV purification. My friend Denis Odinokov suggested to make a system to clean external air, which should consist of a tube with HEPA filter, ventilator and UV light source, which will create a positive air pressure inside the apartment. I think it is too difficult to hand-make at home. But it is another business opportunity of our time.

Just pointing out quickly that this was also posted on Lesswrong and that there are 39 comments with additional discussion over there (as of July 2023).

In a scenario where this tech works as well as we are dreaming of and has generalized in hundreds of millions of buildings: isn't there a risk of a general weakening of our immunity systems, making us more vulnerable over the medium-long run? 

Basic logic behind this question: certain/many classes of virus eradicated from many modern buildings => our bodies are generally less prepared to encounter it in other settings.

(epistemic status: I'm very ignorant in these fields)

I'm interested in the $10 million per minute number. What is the model? Is that for the whole world?

Quick check is that U.S. GNP for one year is $10^12 ( source: https://www.google.com/search?q=us+gnp ), $10 million = $10^7 and there are about 10^6 minutes in a year, so we're saying that the shutdown would be equivalent to turning off the entire US economy.

This has come up a lot, for example I was involved in discussions with Delhi and Seoul airport about installing a UV disinfector for baggage handling. We couldn't get good evidence in favour, whereas the evidence for ventilation was strong. It might be useful in very clean contexts, or changing rooms, or where ventilation/hand washing is not possible. A prime concern is that UV depends on line-of-sight, and sufficient time and proximity to the UV source.

I think there is evidence that wind or ventilation is highly effective both in hospital and domestic/public settings ( see findings tab of covidinfo.info, staff safety section ) as long as not with air lower than 40% relative humidity.

Are you sure hand washing, bleach/cleaning, humidity control and maybe room ionisers wouldn't be more reliable, effective and cheaper, perhaps in combination with ventilation?

Also, for those with high prevalence deficiencies, secondary prophylaxis with Zn, Se, D3 etc and co-factors for absorption from gut (Mg) or into cells (quercetin) could be very cost-effective, as it's already recommended for other health reasons, especially daily vitamin D.

Considering just one of those, humidity, here are two papers and a podcast on the role of humidity in preventing infection and (surprisingly) reducing severity:




Generally, with COVID19 and its virus, whenever an article is confident about a single technical or medical fix, I have found it worth being skeptical, and interrogating the data, and comparing to other options, especially if they seem boring, unglamorous, hard work or expensive by comparison.

Curated and popular this week
Relevant opportunities