What is Far-UVC?

What is Far-UVC?

Far-UVC is ultraviolet light with a wavelength of about 222 nanometres. Like the UV lamps hospitals have used for decades, it inactivates viruses and bacteria. Unlike them, it is absorbed within a few thousandths of a millimetre of anything it hits, so it is stopped by the dead outer layer of skin and by the tear film of the eye before it reaches a living cell. That is why it can be used in a room full of people, and ordinary UV cannot.

Where it sits in the spectrum

Sunlight contains UVA and UVB. Neither UVC nor Far-UVC reaches the ground, because the ozone layer absorbs it, so neither people nor germs have ever had to cope with it. The UV lamps in air conditioning units and sterilising boxes run at 254nm. They are very good at killing germs and they also burn skin and eyes, which is why they only run in empty rooms and sealed ducts. 222nm sits further down the spectrum, where the light is absorbed so strongly by protein that it never gets past the surface of the skin.

How does it work on viruses?

A virus is less than a thousandth of a millimetre across and a bacterium not much more. 222nm light goes right through them. The light is absorbed by the genetic material and the proteins inside, damaging them so the organism can no longer copy itself or infect a cell.

The effect builds up with the dose, which is measured in millijoules per square centimetre. In the main study, from Columbia University in 2020, 1.2 to 1.7 mJ/cm² inactivated 99.9% of airborne human coronavirus. A 2018 study from the same group found that 2 mJ/cm² inactivated more than 95% of airborne H1N1 flu. You can read the 2018 paper here and the 2020 paper here.

Why is 222nm different from 254nm?

Both kill germs. The difference is how far the light gets into tissue. A living skin cell sits under a layer of dead cells about a hundredth of a millimetre thick. 254nm light gets through that layer and damages the cells beneath, which is what causes the sunburn-like reaction and, over time, the cancers. 222nm light is used up in the dead layer. In the eye, less than 0.001% of it gets through the tear film. In the same animal study, 254nm light produced DNA damage and skin changes; the same dose of 222nm produced nothing the researchers could tell apart from unexposed skin.

Where does the light come from?

The ProTech 2, like most Far-UVC devices, uses a krypton chloride lamp. An electrical discharge through the gas produces light with a strong peak at 222nm. The raw lamp also gives off a little light at longer, more harmful wavelengths, so a filter sits in front of it to take those out. The filter is the important bit. The safety studies were done with filtered lamps, and an unfiltered lamp is not the same product. We use Ushio's Care222 filtered module.

Does it sterilise the area?

No, and nothing does in a real room with people walking in and out. The aim is to keep the amount of live virus and bacteria in the air and on the surfaces down to a level where the risk of infection is small, all the time, rather than clean the room once and watch it fill up again. Far-UVC does this continuously and silently. It does not replace cleaning, hand washing or food hygiene; it covers the gap they leave, which is the air.

What it does not do

It only treats what the light reaches, so a surface in shadow or inside a cupboard is untreated. It takes minutes, not seconds, to bring airborne virus down at the dose we use with people present. And some viruses are tougher than others: norovirus has no outer envelope and needs a higher dose than flu or coronavirus, and a surface covered in dried vomit shields the virus underneath it, which is why cleaning after an incident still matters.

Read what the studies found, why it is safe, or how it compares with the alternatives.