More, cheaper, lamps
Right now, if you want to get 222 nm ultraviolet light (the standard for far-UVC), you need what’s called an excimer lamp. These work the way fluorescent light bulbs do: by putting an electric charge into a tube containing a gas, forcing the gas to emit light. You can use different gases and interacting elements to get different wavelengths of light; in far-UVC, the usual combination is krypton and chlorine gas.
This approach has a few problems. Krypton-chloride lamps produce mostly 222 nm light, but not exclusively. Excimer lamps have to include filters to avoid emitting other wavelengths; some filters work better than others, and a malfunctioning filter could be a safety risk by letting more dangerous wavelengths through. The krypton-chloride tubes also don’t last forever and have to be periodically replaced, raising the price of far-UVC disinfection.
The dream, then, has been “solid-state” lamps. These would forgo the gas-in-a-tube approach in favor of mechanisms that emit only a specific wavelength of light. The most prominent approach to date has been LEDs, like those used in computer/TV screens and in modern light bulbs. LEDs get less efficient the shorter the wavelength you use, which poses a challenge.
That said, we did eventually get LEDS that emit blue light, which is on the short end of the visible light spectrum, and startups like NS Nanotech have come a long way in making LEDs for far-UVC.
The big news this week, though, is in another approach: secondary harmonics. Basically, you can design crystals that, when lasers are shot through them, double the frequency of the laser light, which halves the wavelength. So if you shoot a 444 nm blue laser into an appropriate crystal, you get exactly 222 nm far-UVC light back.
Emerging from stealth this month, Uviquity, a Raleigh-based startup staffed by a group of veteran photonics engineers and backed with $6.6 million in seed money, told me they have gotten this process working in their lab. Blue lasers are an old technology at this point (they’re where the name Blu-ray comes from), and have a mature supply chain, meaning building them is relatively cheap and easy.
The crystal that Uviquity uses is made from aluminum nitrate, which is not exactly hard to come by — “aluminum is plentiful and nitrogen is plentiful,” as CEO Scott Burroughs told me. “It doesn't require a whole new technology or infrastructure in order to build these devices,” Burroughs continued. “Once we realized that, we also realized just how well positioned this would be in order to scale up very rapidly.”
It’s hard to overstate the importance of this kind of far-UVC emitter, once it goes to market. It could enable far-UVC lamps to see cost reductions mirroring the drastic drops seen in LEDs and other chips over the years. Making far-UVC disinfection exponentially cheaper could start to make the idea mainstream and speed adoption.
Something in the air
A big part of the appeal of far-UVC is that, unlike higher-wavelength UV — which can cause sunburns, cataracts, and worse — far-UVC is safe for humans’ eyes and skins. But its effect on air quality has been less clear. As I explained in my piece:
When far-UV light hits oxygen molecules, it breaks some of them to form O3 — better known as ozone. Ozone itself is hazardous, and responsible for about 365,000 deaths a year worldwide. Ozone also interacts with volatile organic compounds (VOCs), small carbon-based molecules suspended in the air … These compounds interact with the ozone to create particulate matter. And particulates in the air — smog, basically — can also kill.
That sounds bad, but the basic chemistry leaves a lot of important questions unanswered. How much ozone and particulate pollution do far-UVC lamps actually make in practice? How hard is it for ventilation to clear that up? Are the levels of additional exposure big enough to be a major concern?
There’s still a lot we don’t know here. As a new report from the research group Blueprint Biosecurity explains, a lot of the uncertainty about far-UVC-related ozone is really uncertainty about why ozone is bad for you.
If ozone’s effect on mortality is because of ozone itself, then ventilating rooms indoors could be harmful; there’s more ozone outside than inside, and better ventilation would just pull it indoors. But if ozone is harmful mostly because it creates other secondary pollutants, then ventilation is a good idea.
We don’t know, and that makes understanding the best way to use technologies like far-UVC and ventilation very difficult.
That said, some new research is making me tentatively more optimistic that the ozone effects of far-UVC are not concerningly large. One recent paper studied an office where either one far-UVC lamp (as recommended by the manufacturer) or four (way in excess of recommendations) were placed. The single lamp didn't do anything to ozone or particulate levels in the room. The four lamps did. The conclusion, then, is that if used in moderation, far-UVC lamps could disinfect without ruining indoor air.
Another paper did find modestly higher ozone levels with a single far-UVC lamp — but it found that if the lamp is placed on the ceiling, it both minimizes exposure to ozone by humans, and maximizes the lamp’s effectiveness at disinfecting the air.
These are still early days for far-UVC, both in the engineering challenge of designing cost-effective lamps, and in the epidemiological challenge of understanding its effects on the air. What we need more than anything is additional research.
But I am modestly more confident than I was last year that we’re heading toward a world where these lamps are ubiquitous. Potential pandemic threats, like bird flu, or even a new dangerous respiratory virus engineered in a lab with the help of AI, would face a formidable new foe that can kill them in midair. With luck, in 10 or 20 years, childhood flus, tubercular infections, and even pandemic viruses could be withering away due to the efforts of this new weapon.
—Dylan Matthews, senior correspondent and lead writer
