In January 2024, I wrote a big piece on a relatively new, and very promising, approach to fighting respiratory diseases like Covid, tuberculosis, and flus. It’s called “far-UVC,” a type of ultraviolet light, at wavelengths of roughly 200 to 235 nanometers, that can kill the vast majority of airborne pathogens it targets, without damaging human skin or eyes the way longer-wavelength UV does.

The potential here is massive. Imagine being able to place a few lamps in key rooms where disease transmission is common — like schools and daycares, hospitals, retail stores, and offices — and kill off the vast majority of diseases being spread through the air. The benefits, both in immediate public health and the ability to head off the spread of pandemics like Covid in their early days, would be massive. The lamps can kill over 99.9 percent of Covid viruses in the air — and would be similarly effective against new outbreaks that spread through the air.

So why don’t we have far-UVC in operation right now? There have been at least two major factors holding the tech back to date, but in the year and a half since my piece came out, we’ve gotten some promising information on both of them.

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........

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