UV 222 – Safe for exposure and effective at eliminating microorganisms?

Apr 25, 2022

A UK study published by Scientific Reports in March 2022 showed UV light at a 222 nanometer wavelength emitted from krypton chloride lamps inactivated Staphylococcus aureus bacteria and proved safe for human exposure. UV light is a long proven technology for inactivating bacteria and viruses and is widely advocated by ASHRAE and the EPA. The common concern about traditional UV applications is its hazardous effect of direct exposure to skin or eyes caused by improperly deployed systems. In this blog we will discuss UV 222 and details of this latest study.

Background on UV

According to the World Health Organization, UV light falls between ~ 100 nm and 400 nm. This is between the visible spectrum and X-Rays. UV light is divided into three different categories. UVA (315 to 400 nm) – responsible for skin tanning effect, UVB (280 to 315 nm) – responsible for delayed tanning and skin burns and UVC (~100 to 280 nm) – the most damaging variety used for its germicidal qualities. A 1942 study showed a reduction in transmission of measles and mumps in irradiated classrooms with UV 254 with the downside of skin and cornea damage with direct exposure.

UV 222 from Krypton Chloride Lamps

The properties of krypton chloride (KrCl) lamps allow it to emit 222 nm wavelength (rather than 254 nm) while filtering other wavelengths that may cause adverse health effects. According to the study, 222 nm wavelength had minimal negative impact on health. However, another study shows that these lamps did not fully eliminate other wavelengths and have exposures outside the safe range of 207 nm to 230 nm. This second study stated that these lamps should be treated the same as other UV based lamps.

3D schematics of the bioaerosol chamber configuration showing room dimensions, the position of the lamps, pathogen source and collection point (top) with an illustrative example of the Far-UVC lamp emissions (bottom).

How the UK Study was executed

Using a 14 square meters chamber, the room was provided with ventilation and 5 KrCL based lamps at a height of 2.12 meters aimed toward the chamber bottom. The ventilation provided three-air-changes per hour. The area was sampled for up to 50 minutes with high, medium and low intensities. The results showed high intensities reduced 98% of airborne Staphylococcus aureus, medium intensities reduced 92% of airborne bacteria and the low setting reduced 29% of airborne bacteria. For each of the tests, industry exposure limits for UV were not exceeded.


While the UK study on UV 222 shows promise at eliminating adverse effects of UV while still delivering on germicidal qualities of UV 254, data is still inconclusive. If you are considering UV or any other air cleaning technology, we encourage you to reach out to Indoor Science for a consultation.