Far-UV: An Early Adopter Lay Person’s Pespective


I hope this presentation will give you an idea of things to consider when looking into “far-UV” (or UVC) devices, which can be a great additional weapon in our arsenal against SARS-CoV-2.

I want to make clear up front that I’m not an engineer or UV/clean air expert: everything in this post/presentation is from what I’ve learned from extensive research into this topic, capped off by buying two of the devices we’ll be talking about shortly.

Also, I haven’t and don’t receive any compensation in any shape or form from any of the companies I’ll be talking about. All opinions (and any mistakes I might make in the following sections) are my own.

What I’m going to talk about: - Far-UVC: What is it? - A super-interesting experiment! - Power, Distance, and Time + Inverse Square Law - Ergo X-One - Krypton Shield - Sterilray GermBuster Sabre - Early Adopter Phase Issues, Concerns - Conclusions - Sources & Resources

This is a summary of what I’ll be talking about. No need for me to repeat it all! 😁

Far-UV: What is it? We’ve known for about 80 years that ultraviolet (UV) light kills pathogens BUT…ultraviolet light can also damage our skin & eyes Longer wavelengths (UVA and UVB) are harmful “Far-UV” (or UVC) is a band of shorter wavelengths

It’s not new that UV light can kill pathogens. But the longer wavelengths (UVA and UVB) are NOT safe for people!

222 nm Far-UV When I say “Far-UV or Far-UVC,” it refers to 222 nm UVC 222 nm UV was patented by Ed Neister as a highly effective means to destroy pathogens (SterilrayTM) (US9700642B2, 11 July 2017) Significantly more effective vs. viruses than longer UV wavelengths SAFE for extended exposure to people!

Well, I decided NOT to do the video (I ramble too much, lol), but the slide above gets the point across. The key things are that 222 nm UV is HIGHLY effective in killing pathogens AND it’s safe for extended exposure for people.

This is from “Far UVC Radiation: An Emerging Tool for Pandemic Control. The link to the article is in the sources section at the end of this post.

The abstract above gives a good overview of the critical aspects of 222 nm in terms of how it affects people: in short, it has an EXTREMELY hard time penetrating the outer layer of our skin and the liquid surrounding our eyes. While you certainly can get too much exposure, you really have to abuse these devices to overdo it. Make SURE you read the instructions and understand how to use the tool.

This is an extract from Real Nano “Light Vaccine” Will end fit To COVID-19 Pandemic Control, with the source at the end of the post.

The takeaway from this extract from another study is, again, that 222 nm is highly effective against pathogens, particularly coronaviruses. It’s combination of lethality to viruses and safe employment around people could revolutionize our ability to kill SARS-CoV-2 and other harmful virus and bacteria.

From Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber, showing the diagram of the test room with 5 222 nm lamps.

In the above diagram, you can see in this experiment how 5 222 nm lamps were installed, along with an air inlet and outlet to provide controlled airflow, as well as a pathogen source and a sample point to monitor how much pathogen remained. The key thing here is that the pathogen (a benign virus) wasn’t just injected into the chamber once and left alone; it was pumped in continually throughout the test to simulate an infected person exhaling it.

From Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber, a chart showing the inactivation of the test pathogen over time, using 5 lamps and 1 lamp, in both cases on the high setting (I’m assuming 15 watts).

In the above chart, you can see that 1 lamp inactivated 90% of the bacteria and 5 lamps inactivated roughly 99% in about 15 minutes, after the “infected test subject” was exhaling into the chamber for 50 minutes prior to the lamps being switched on. Then the lamps maintained that level of inactivation, even though the pathogen inlet was still pumping bacteria into the chamber.

In practical terms, most of us couldn’t afford five 15 watt lamps, but we might be able to afford one. That would have a huge reduction capability in, say, a dining room, and when combined with HEPA filtration, Corsi-Rosenthal boxes, and/or ventilation, could drastically reduce the risk of exposure in that space.

Power, Distance, and Time Before buying a far-UV device, you need to understand the relationship between Power, Distance, and Time for Exposure: Power (Watts): more > greater range > more exposure > kills virus faster + shorter safe exposure (and vice versa) Distance from lamp: farther > less exposure > kills virus slower + longer safe exposure (and vice versa) Inverse Square Law: half the distance = 4X the power, twice the distance = 1/4 the power, 3X the distance = 1/9 the power, etc.

Unlike HEPAs, which can be sized to a given room volume to provide a given number of air changes per hour and then left alone, far-UV devices use light that brings with it the need to understand the relationship between Power, Distance, and Time, along with the critical impact of the inverse square law.

Diagram illustrating the inverse square law, with 9 photons passing through a given area at distance r, then 4 times that area at distance 2r, and then 9 times the area at distance 3r.

You need to have a grasp of the inverse square law because it has a huge impact on how much the light from a lamp dissipates over distance. At a distance of 2 feet from a lamp – irrespective of the lamp’s power – the power is only one fourth the power at one foot; and at three feet, it will only be one ninth. The upshot is that it will take a LOT longer to kill viruses the farther away you are from the lamp.

On the flip side, power goes up when you move closer: from three feet to one, for example, the power jumps up NINE TIMES.

So, distance (combined with power) matters a LOT when considering whether a given far-UV device will work for a particular use case. Exposure always has to be taken into consideration, but in general closer is better: more power on target kills viruses faster.

There are MANY potential use cases: Together with filtration/ventilation or on its own, depending on use case, 222 nm UVC could radically reduce transmission in: Hospitals, medical clinics, dental clinics Schools Theaters Restaurants & Bars BusinessesAnd more…

While far-UV is only A tool and not THE tool, it has many potential use cases, both used by itself and in combination with filtration and ventilation.

Now let’s take a look at a few products:

The Ergo X-One

The Ergo X-One

The Ergo X-One is a small, palm-sized low power device marketed as a solution for personal protection in environments like restaurants, on planes, or other situations where you want a one-person protective shield from airborne pathogens.

Ergo X-One: Personal far-UV device Power: 3W Weight: 5.3 oz Size: 3.1 x 3.4 x 1 inches Battery: 4 hrs Warranty: ? Price: $2,688 HK (Don’t panic! This is about $340 USD)

The above slide shows the basic stats on the X-One. Note the power is only 3 watts – this is VERY low. I couldn’t find any warranty information, but for the sake of argument I’ll assume it’s one year. And don’t let the price listed on the buy page fool you: it currently retails for about $340 US.

But the question is, does it work? Can it do what the manufactures claims? Let’s take a look.

Per the manufacturer, the X-One produced a 1-log (90%) reduction in aerosols for these times at the given distances from the lamp. I wasn’t able to find information on the test pathogen(s). Inactivation times vary widely, but SARS-COV-2 inactivates more quickly under far-UV than many other pathogens.

The chart shows Ergo’s claims for how long the X-One takes to produce a 90% reduction in aerosols for various distances out to 75 cm. I couldn’t find any information on what microbes were used to establish these figures, unfortunately.

Let’s look at the times. I measured the distance from about an inch above our dining room table to the tip of my nose: 17.5”, which is about 44.5 cm. At that distance, according to the chart, the X-One would take about 30 seconds to inactivate 90% of their test pathogen. That’s a LONG time, and I can’t believe I wouldn’t inhale a considerable amount of the pathogen in those 30 or so seconds. A lot depends on air flow and other factors, but that doesn’t give me warm fuzzies, to be honest.

Chart showing time versus distance to inactivate 90% of test pathogens by the X-One, both with manufacturer data and estimated data from a review by Joey Fox (@joeyfox85) on Twitter.

One of the biggest factors is what type of pathogen they used: bacteria tend to take longer/more exposure to destroy than, say, coronaviruses. So I plotted the manufacturer data alongside some data I put together based on a review of the X-One by Joey Fox (@joeyfox85) on Twitter (note: any errors or screwups here are mine, not Joey’s!), where Joey estimated the inactivation time for SARS-CoV-2.

The blue line shows Ergo’s data, the green line show’s the extrapolation of the SARS2 figures. At 50 cm (19.6”), 15 seconds or so is a lot better than 31.5, but still isn’t great. When you get down around 25 cm – half the distance, quadruple the power, remember? – things start looking better. Remember, this is the time to inactivate 90% of the pathogen/virus. So 4-ish seconds is a lot better than 10.5.

But is that fast enough? That’s the question, isn’t it? And that’s a conundrum for early adopters like myself: I don’t want to experiment on myself with this stuff, but the technology can never be proven in the real world unless we learn what we can and apply it.

Now, would I trust it to protect me at a restaurant? No. Would I use it on a plane? Yes, as an extra layer of protection, or if I needed to eat (keep in mind some people MUST eat at periodic intervals), it would provide some protection by keeping my face low toward the tray table, especially if I coordinated it with low(er) CO2 readings from a monitor.

Why I chose the X-One: I wouldn’t trust it to keep me safe by itself at a restaurant, for example: I don’t think it can’t kill virus quickly enough at a practical distance But it CAN reduce risk & provide another layer of protection At the dentist (1/2 distance = 4X the power) Additional protection on planes or in the car, or anywhere you may need to briefly unmask People have put it on hats and other ingenious applications (see @RealSexyCyborg on Twitter)

Yes, I did buy an X-One – a pair, actually (they discount a bit if you buy two). But I bought them for specific niche use cases as you see above, not the ones touted by the manufacturer. Three watts just isn’t enough power, in my non-engineer opinion. Now, if they came out with a similar device that was maybe 10 watts or so – that would be a different matter!

Krypton Shield

The Krypton Shield

Now let’s take a look at the Krypton Shield, which is a pretty popular device in the 15W range. This is where most consumer products are found – 10 to 15W – from a variety of companies.

Note that I don’t own this one.

Krypton Shield: Power: 15W Weight: 3.7 lbs (includes stand) Dimensions: 30.5” x 8” (shipping box) Warranty: 1 year Claimed range/area of “disinfection”: 1,500 sq ft (~39 x 39 ft) (“Up to an additional 8 eACH”) Price: $2,500 USD

As you can see in the screen shot of the manufacturer’s web site in the previous image, the Krypton Shield is intended to be used on a stand, and that accounts for its weight and dimensions (for the shipping box).

The claimed area of “disinfection” is 1,500 square feet, equivalent to about 39 by 39 feet, and can provide up to an additional 8 estimated air changes per hour (eACH).

If you think back to the distance and time for 90% inactivation chart for the X-One and how long it took with distances under a meter (or half a meter), I find the claim that the Krypton Shield – which is only 5 times more powerful – can disinfect 1,500 sq ft (39’ x 39’) pretty tough to swallow. Technically, yes, I’m sure that at those distances the light is still zapping microbes, but the inactivation times are likely a matter of minutes, not seconds.

Specs of the Krypton-11

Taking a look at another Krypton product, the Krypton-11, we see that it’s a 15 watt device intended to be mounted on the ceiling, similar to the devices used in the experiment in the room-sized chamber we talked about earlier. In this case, the figures are a bit more believable: a 3 log+ (99.9%) disinfection coverage of up to 400 (20 x 20) sq ft per fixture, although even that is still probably stretching it. What they don’t tell you, unfortunately, is how long achieving that level of infection takes at various distances from the lamp: remember Power, Distance, and Time.

However, based on the experiment with the room-sized chamber, I would buy that a Krypton-11 or similar 15 watt device would be able to zap 90% or more of coronavirus in a room of roughly 150 sq ft (again, heartening back to the test chamber earlier).

Krypton’s “Disinfection” definition: All references to “disinfection” are referring generally to reduction of bioburden and are not intended to refer to any specific definition of the term as may be used for other purposes by the U.S. Food and Drug Administration or the U.S. Environmental Protection Agency. The disinfection technology as incorporated in Far UV Technologies products is not intended for use in the cure, mitigation or prevention of disease and is not certified or approved for use as or for the disinfection of medical devices by the FDA. Bioburden reduction is a function of fixture run time, distance to the UV light source, air flow, room size, shadow areas and/or other factors, and the level of reduction will vary within a specific space.

Krypton also has a pretty impressive caveat for “disinfection.” I’m not necessarily trying to ding the company for this, but am using it as an illustration of how vague and malleable a lot of the information is about these devices and how best to use them. And, again, I think Krypton is really overstating the capabilities of the Krypton Shield with the 1,500 sq ft number.

Now let’s take a look at a couple use cases:

Dr. Ashish Jha in a room with people, three Krypton Shields arrayed behind the podium and lecture area.

The above photo shows Dr. Ashish Jha, one of my least favorite human beings, giving a lecture. Behind him you can see three Krypton Shields, with what looks like might be another far-UV device in the upper left corner near the screen. In this case, Jha is likely well protected, but the inverse square law means that protection is going to fall off rapidly for the folks farther away. And you can tell this was taken earlier, when more people took the pandemic seriously, as many in the audience are wearing masks.

But, Jha notwithstanding, knowing what I know as a lay person who’s looked into this technology a lot, I would hazard to say this is a good use case. Using multiple devices like the Krypton Shield in various configurations at moderate range (I’m guesstimating here, but let’s say 10-15 feet) could provide good protection to a decent-sized area, especially when combined with HEPA or Corsi-Rosenthal boxes and/or ventilation.

The Krypton Shield used in a dining room or kitchen setting.

The above photo, taken from the Krypton Shield web site, shows what I suspect is a great use case for this device: protecting a dining room setting, where lots of aerosols are going to be generated. An overhead lamp would no doubt be better and provide more even illumination/microbe killing power, but at distances of, again, 10-15 feet, I’d accept that the Krypton Shield could provide good protection (ideally with HEPA/CR box and/or ventilation, as well).

Sterilray Sabre

The Sterilray GermBuster Sabre

The Sabre is, as far as I know, the most powerful 222 nm device available in the consumer market, and – IMHO – has the widest range of potential applications. It’s also, sadly, the most expensive by a considerable margin. Note that the photos of the Sabre were taken from Sterilray’s web site.

Sterilray GermBuster Sabre Portable far-UV device for rooms and larger areas Power: 150W Weight: 3 lbs 6 oz Dimensions: 30” x 3.5” Manufacturer estimated “highly effective” range: ~70 ft 110V or EGO batteries (2.5 Ah recommended = 69 minutes) Lamp warranty: 4 years Price: $4,300 USD

With 150 watts, the Sterilray Sabre is 10 times more powerful than the Krypton Shield, although it’s roughly the same size and weight with the Krypton Shield’s stand retracted. While it’s not published as such, in discussions with the manufacturer, they believe the Sabre is “highly effective” out to roughly 70 feet; even if you didn’t believe that, with 150 watts of power, I’d certainly believe it’s extremely effective out to 30 or 40 feet. The Sabre is covered with a 4 year warranty, with a projected lamp life of 30,000 hours.

An interesting feature of the Sabre is that it can be plugged into a 110V outlet or powered using a DC adapter and a 2.5 Ah EGO battery from the EGO line of lawn care products, which gives an untethered power source for up to 69 minutes.

A classroom setting with a Sterilray Sabre sitting on a wall mount.

The photo above shows a classroom type setting with a Sabre perched on dedicated door mounts (in this case mounted on a white board). While I would orient the device more toward room center, I personally believe it would provide excellent protection to this entire space. This is a use case of specific interest to me, as my wife takes and gives classes in very similar settings to this one.

Sterilray Sabre on a vertical stand in a dining room area and near a Christmas tree.

The above shots show a Sabre on the optional vertical stand, providing protection for a dining room and a living room during the holidays. While potential overexposure has to be kept in mind, according to the manufacturer, you could be exposed to the Sabre for 24 hours at 10 feet and not exceed the threshold exposure limit for skin (although with eyes you have to be more careful). But that would literally be standing still, which likely isn’t going to happen in these scenarios. As above, this use case is of direct interest to me, as we have family members and friends who’ve long since given up masking.

The Sabre providing protection at a dentist’s office.

While it would be nice if dentists, medical practices, and hospitals would provide protection to their patients, it’s up to us individually in this obscene “you do you” environment to try and keep ourselves save. In the above photo, the Sabre is providing protection in a dental office. In this case it’s hooked up to an EGO battery. Note that this would also be a great scenario for using the Krypton Shield, and you could combine it with something like the X-One (held in your hands as close as possible to your mouth and nose) to provide more protection. And, of course, people also use personal and even larger HEPAs, but the benefit of far-UV is that it kills quickly (when in “effective” range), faster than HEPAs can cycle the air.

Portable (including w/EGO battery) high-power far-UVC protection: Business events (e.g., hotel ballroom settings, classes, etc.) Hotel rooms (like where my wife and I were infected) Gatherings with friends, family Medical procedures that may require unmasking

Yes, I bought one. Because of the price, this was NOT an easy decision. But after COVID-19 finally caught up to us at the beginning of Mach 2023 (I believe from lingering aerosols in a hotel room), the decision became a lot easier: I do NOT want to get hit with this virus again, and ditto for my wife. But I also had very specific use cases, mainly protecting my wife during business events and myself if I have to travel for work. Those and others as I mentioned above drove this investment decision.

Yes, I bough a Sterilray Sabre.

Is it safe to unmask while protected by a device like the Sterilray Sabre?

I know I’m going to upset or shock some people, maybe many people, but yes, within a range of 30 to 40 feet (although closer would be better!), I think I would feel pretty comfortable unmasking while protected by a Sabre. Granted, I wouldn’t try it in a bar where near field aerosols would likely be super dense, but a family gathering with non-masking family and friends or a business event…yes. It would be absolutely surreal, yes, but I trust the science and technology (and the Sabre’s 150 watts) enough to do it. Note that I would also use the Sabre outside (BBQ, birthday party, that sort of thing) to help further reduce the risk of transmission, as we know that outside infection can indeed happen.

Now let’s talk just a moment about why I would even consider unmasking “under the light” rather than using it only as an additional mitigation on top of masking (which, of course, is perfectly fine!!). My friend, I don’t believe things are not going to improve in terms of society recognizing the pandemic is real any time soon. Our leaders aren’t going to have a change of heart, our fellow citizens, friends, and family who have “moved on” aren’t going to suddenly have a mass epiphany and row back upstream to where we are – that could happen eventually, but I’m not optimistic. Instead, social and economic pressure is rapidly growing on those of us who are still masking. This is, I believe, having a direct impact in terms of lost business on more and more people because an increasing number of patrons or business affiliates don’t want to do business with folks who are still masking. We’re being painted as fringe lunatics, and that image is gaining more traction every day.

Now, it’s easy to say, “To hell with them!” But that’s not an easy, or even workable, option for more and more people who are trying to keep their businesses afloat, or who are being forced into workplaces that are unsafe and being pressured to lose their masks. I think this anti-mask trend is just going to continue gaining steam, and customers and business partners in most cases have other options and can just walk away, and bosses can and will make demands that put people in danger. Small business owners, in particular, can only endure so many losses like that before they start suffering serious pain, and not all of us can easily walk away from our current jobs and find new ones (with very few employers being “COVID aware”).

I believe that far-UV/222 nm technology, properly employed, may help us bridge that gap, at least in certain situations, and also add an excellent layer of protection on top of masking, HEPAs, CR-boxes, and ventilation (plus CO2 monitors) in many other settings. While we have little control over institutional adoption of this technology, consumer devices can help us stay safe in unsafe workplaces. They can help people safely (or with vastly reduced risk, since few things are truly “safe” nowadays) connect with business affiliates and customers. They can help improve safety during travel (especially in hotel rooms when you can’t travel with a full-size HEPA). They can keep our elders safer in long-term care facilities that have become slaughterhouses for our parents and grandparents. Portable devices like the X-One – although I’d like to see more powerful versions – can help keep our kids safer/reduce risk in our in-person educational Petri dishes.

Again, far-UV isn’t “the” solution, but it’s a powerful addition to our arsenal that can expand our ability to block transmission chains, either used alone when other tools aren’t practical or available, or used in tandem with masking, room/building filtration, and ventilation.

HOW I bought a Sterilray Sabre It’s currently sold direct through Sterilray and Wayfair Wayfair had a sale with a SIGNIFICANT discount Wayfair offers 24 month 0% interest financing Will be taking a 2023 tax deduction for business use

Of course, WHY I bought it likely isn’t as much interest to you, I’m sure, as HOW I could afford it. I’ll say right up front that I understand this kind of thing is currently for those of us who live in privilege, and one of the reasons I’m preaching about this technology is to help speed up adoption and mass production that can make it more affordable for everyone. Frankly, I think the government should put far-UV devices into production under the Defense Production Act, but that’s another thing.

The bottom line is that I was able to get it on sale at Wayfair at a significant discount, and they offer 24 month 0% financing that made the monthly payment do-able (note: I got mine just before a major price increase due to a recent increase in the price of component parts). On top of that, since I bought this for mainly for business purposes, I’ll be writing most of it (minus personal use) off on our 2023 taxes.

Again, something like the Sterilray Sabre isn’t necessarily for everyone, even if it was much less expensive. But for the specific use cases that drove my purchasing decision, I believe it was a sensible investment.

Cost ratios comparing the X-One, Krypton Shield, and Sterilray Sabre

One thing I did want to touch on, once you pick your jaw up off the floor from the Sabre’s price tag, is some basic cost ratios. While the Sabre, for example, is far more expensive than the Krypton Shield (let alone the X-One), in terms of dollars per watt of power it’s a steal: 29 versus 167 for the Krytpon Shield and 113 for the X-One. Also, the warranty is four times longer than the Krypton Shield (and presumably the X-One).

While I couldn’t find the expected lamp life for the Krypton Shield, the life of the lamp for the 15 watt Krypton-11 was listed as 9,000 hours, less than a third of the Sabre’s. That translates to 143 dollars per thousand hours for the Sabre versus 278 for the Krypton-11 (and I’m assuming the same for the Shield). This means that for the $4,300 investment for the 30,000 hours (and 10 times more power) of the Sterilray Sabre’s lamp, you’d have to buy four (technically three and a third, but since you can’t buy just a third of a device, you’d have to ante up for the fourth) Krypton Shields for the same amount of use: that would translate to $10,000.

My point here is not to say that everyone needs a Sabre, but to illustrate some of the qualitative value that products like the Sabre bring to the table that’s hidden behind the breathtaking price tag. And that’s something you REALLY need to consider if you plan to use these devices a lot.

Now, having said that, there are no doubt use cases where you might want to have, say, several far-UV devices to cover either oddly shaped areas where the light from a single device can’t reach, the far end is too far for effective coverage, or you’re covering a more closely spaced group of people and need multi-directional coverage to minimize shadowing (someone standing between you and the lamp: any aerosols in that “shadow” won’t be killed until they enter the light, and you don’t want to breathe them in; this might be addressed in some situations with fans to keep the air moving and/or elevating the lamps or mounting them to the ceiling to provide “look down” coverage). Which devices, again, depends on your intended use case. If you want to cover a hotel ballroom, say for a huge wedding reception or a big business event, you’re going to need a few high power devices like Sabres. If you’re covering a smaller event, a few Krypton Shields might do the job.

Granted, there are issues with potential liability, insurance, and so on, but I’d love to see entrepreneurs set up businesses providing far-UV event protection…IF there was enough demand. That, I think, is the problem right now: there just aren’t enough people who give a damn about protecting others from transmitting SARS-CoV-2 (and other pathogens in circulation!) to create a sufficient demand for this sort of service. Another idea would be to learn enough to provide consulting services for businesses, schools, etc., that might be interested in deploying this technology on an institutional basis. Again, however, I don’t see any indication the demand is there – yet, at least. I would love to be wrong, however!

WHy are Far-UV Products so Expensive? Relatively new technology Not enough demand (yet) to drive more production > economies of scale > reduced prices VCR player in 1977: ~$5,000 in adjusted dollars CD player in 1982: ~$3,000 DVD player in 1996: ~$1,000

The bottom line for why these devices are so insanely expensive is really that the technology is in its infancy on the consumer market, just as VCRs, CD players, and DVD players were in years past. They were all insanely expensive when first introduced, but early adopters helped drive demand, demand resulted in production that achieved economies of scale, and that lowered prices. As I think I mentioned earlier, this is why I’m preaching about this technology: we KNOW far-UV/222 nm is an extremely efficient killer of pathogens and is safe for extended exposure. We just have to drive demand that will eventually make this more affordable for more people, and lead to a wider range of more effective devices.

What About Filters? Many 222 nm lamps have filters to suppress dangerous wavelengths Some, like Sterilray’s, are designed to suppress those wavelengths without one Some believe filters are essential; some do not Who’s right? Depends on who you ask & trust

I’m bringing this up because this is big point of contention among different engineers and experts. The point of filters on 222 nm lamps is to make sure the longer – harmful – wavelengths are suppressed. This is especially the case with many of the cheaper lamps that could be dangerous without a filter (but some of the super cheap ones have crappy filters, too – be careful what you buy!). However, some lamps, like Sterilray’s, don’t have filters because they’ve been engineered to suppress those wavelengths as part of the lamp design. The “you must have a filter” folks have issues with this approach.

For my part, I think it boils down to how well you’ve researched the product and grilled the manufacturer, then you have to decide for yourself. Some of the “you must have a filter” folks are people whose opinions I really value. On the flip side, using Sterilray as an example, the company has been developing this technology since 2005 or so, and after extensive discussions with them, I value their opinion – even though yes, they’re trying to sell a product – as well. Maybe a filter would further reduce any potentially harmful emissions, but from what I (as a lay person) understood, the Sterilray folks seem to know what they’re doing and I had no qualms or reservations about buying a Sabre.

Now, if it was a cheap lamp AND it had no filter, run very far away, as quickly as possible. You don’t want any part of that.

Can you make a DIY far-UV/222 nm device from parts to save money?

My answer to this – again, as a lay person who’s done a lot of research – is no. Please do not do this. It’s one thing for an engineer who really understands this technology (like Naomi Wu on Twitter) to build their own, because they understand the safety issues involved, know how to source quality parts and assemble them, and also have the knowledge and equipment to properly test whatever gadgets they come up with to make sure they’re safe. Buying cheap far-UV lamps to save money and rigging up the power supply, etc., is a great way to potentially injure yourself and others.


Conclusions (1) We KNOW that 222 nm UVC… - Is extremely effective at killing virus and bacteria - Is safe for extended exposure for people One manufacturer theorizes 2 ft of distance per Watt is “highly effective” You MUST learn enough to properly use these tools When possible, combine Far-UVC with good filtration & ventilation

I think most of what’s in the above slide is pretty self-explanatory. One thing I’d elaborate on is the theoretical 2 ft per Watt thing. Is that legit? As a lay person, I don’t know, and it was specifically labeled a theory. But it would be GREAT if we had one or two rules of thumb for using these devices, wouldn’t it? Or an app that we could plug a few simple variables into and know, for a given distance, how long our safe exposure was and how long it would take to kill virus (90% reduction seems to be the typical benchmark, but how long that takes is the big question). Or even some sort of range card that would show us exposure times and 90% viral reduction times for various distances, the minimum safe distance/time, and the maximum “effective” distance/time to kill virus. Far-UV in institutional settings, schools, for example, needs to be carefully engineered. But those of us using consumer products need to have a useful “wind gauge” for real-world use.

Another point to emphasize that I didn’t really make clear earlier: far-UV devices are great at killing airborne pathogens, but they do NOT clean the air. In fact, over time they can create particulates in the air that, in quantity, can potentially be harmful (although this is pretty far out on the end of the safety bell curve and wouldn’t be near the top of my worry list). So, whenever possible, combine far-UV with good filtration and ventilation, which you should be doing as a matter of course because clean air is much better for you!

Conclusions (2) OPINION: People tend to overestimate exposure risk of 222 nm and underestimate device power to sanitize a given space OPINION: Most far-UV device manufacturers are overstating the effective practical range/area of coverage for their products Pathogen inactivation times at manufacturer-stated range/area can be many seconds or even minutes Early Adopters need to adjust expectations and use cases accordingly

Just to ping on a couple points again, I think people hear “UV” and think it’s the “bad” UV and are hesitant to keep these devices close at hand. Again, you do NOT want to abuse the device and need to understand its parameters for safe use, but if you can stand in front of a 150W Sabre for 24 hours at 10 feet and not exceed the daily exposure limit for your skin (again, eyes take less), you could cozy up a bit more to a Krypton Shield, for example, to reduce the kill time for pathogens trying to get to you, and still be well under the daily exposure limit.

As a corollary to that and drive the point home again, many/most manufacturers are overstating what their products can do in the real world. I don’t know about you, but I want to know what the maximum “effective” distance is for a given device so I can make sure those I’m trying to protect are in fact being protected.

Of course, we ALSO have yet to clearly define what “effective” means, right? We don’t have a good standardized gauge for that. Maybe it could be along the lines of “takes X amount of time <some very low number of seconds?> to inactivate 90% <or 99%?> of test virus Y <ideally a human coronavirus> at distance Z” as a standardized threshold. We need something along those lines that we can apply across all these devices to have an idea of where the boundary of safety really starts falling off. Right now, the manufacturers can tell us anything and people don’t know any better.

I suspect those things will come along, but as early adopters we don’t have that advantage and have to figure this stuff out as we go…

Sources and Resources

Far-UV: An Early Adopter Lay Person’s Pespective

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