Why 222nm in Occupied Spaces
Results from laboratory testing and clinical studies suggest that 222nm far-UVC is capable of inactivating viruses and bacteria in short time periods at energy levels that do not harm eyes and skin, allowing it to be used in occupied rooms.
The key property of 222nm far-UVC that makes it different from other UV wavelengths is that the 222nm wavelength easily penetrates and inactivates both viruses and bacteria, while having minimal penetration into the biologically sensitive nucleus of human cells.
Since the proteins on the top layers of our skin and in the cornea of our eyes absorb 222nm far-UVC, the 222nm wavelength does not penetrate these tissues to depths associated with sunburn, skin cancer, cataracts, photokeratitis, and other conditions. In contrast, possible acute and chronic damage to eyes and skin may result from the more generally employed 254nm UV wavelength used in many germicidal lamps, although this UV wavelength can be used in interior spaces under certain conditions that sharply limit human exposure. In addition, although lamps in the 405-430nm wavelength range can also be used in occupied spaces, they are not as effective against viruses as lamps with lower-range UVC wavelengths.
When designing for a proposed space, exposure to the 222nm far-UVC should not exceed the level that a typical worker can experience without adverse health effects. In order to meet the American Conference of Governmental Industrial Hygienists (ACGIH®) safety guidelines for exposure, the 222nm source must generate a narrow band of the 222nm far-UVC without the longer UV wavelengths that are harmful to humans.
The Care222 far-UVC disinfection technology from Ushio utilizes an excimer lamp that employs a specially designed short pass filter to remove harmful wavelengths, resulting in a narrow band of UV centered at 222nm. Excimer lamps are arc discharge light sources with a special chamber filled with noble gas, completely mercury-free and without electrodes. Acuity Brands luminaires with Care222 far-UVC disinfection technology employ proprietary integrated controls to modulate pulses of the 222nm far-UVC for an appropriate dose to operate within the ACGIH safety guidelines.
Bacteria and viruses on surfaces in direct view of the Care222 far-UVC can be rendered harmless when exposed for the appropriate dosage.
An April 2020 study published in Applied and Environmental Biology concludes that a number of human pathogens were all killed or inactivated by 222nm UV at lower fluence rates than with 254nm UV.
Various research studies document the dosing levels of the Care222 far-UVC required for effective pathogen reduction across a wide range of microorganisms.
Acuity Brands’ products with Care222 far-UVC disinfection technology will be designed to operate within today’s ACGIH established safety guidelines. Recent research studies suggest that even higher doses of 222nm far-UVC exposure can be experienced without apparent harm to eyes or skin.
Lighting System Featuring Care222 far-UVC Disinfection Technology Application Design Guide
For UV disinfection systems to be effective and without harm to skin or eyes, these factors are at play:
Safety and effectiveness are both UV wavelength dependent.
In just THREE STEPS, design an Acuity Brands lighting system featuring the Care222 far-UVC Disinfection Technology:
STEP 1 Calculate planar irradiance in μW/cm2 at locations where pathogen reduction is desired and where people will interact
STEP 2 Convert planar irradiance to Dose in mJ/cm2
STEP 3 Confirm design is providing sufficient quantities of the Care222 far-UVC based on expected performance to achieve targeted pathogen reduction within safety guidelines.
The Discovery and Science behind 222nm
The use of far-UVC, specifically the 222nm wavelength, was pioneered at Columbia University. Researchers at Columbia discovered that 222nm far-UVC penetrates living surfaces only by about 1 µm. It does not have enough range to penetrate the dead-cell layer at the surfaces of our skin, nor does it have enough range to penetrate through the cornea to the lens in our eyes. Yet, 222nm far-UVC has enough range to traverse viruses and bacteria which are much smaller in size than human cells, making this an ideal strategy to aid in the reduction of pathogens in public spaces. Learn more here and read the latest published research on coronaviruses.
In addition to the Columbia University research, a joint research study conducted by Kobe University and Ushio concludes filtered 222nm far-UVC radiation causes no injury to human skin. The research results have been published here on the online journal, PLOS ONE.
To see these two references, and many other relevant research reports, view our 222nm Wavelength UV Published Research page.
*All references to “disinfection” are referring generally to the reduction of pathogenic 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 Acuity Brands products is not for use as or for medical devices.
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