Most light radiating devices emit a peak primary wavelength as well as other secondary wavelengths, referred to as spillage wavelengths. Similarly, while Far-UVC excimer lamps emit peak primary wavelengths of either 207nm or 222nm depending on the type of lamp, they can also emit secondary wavelengths below 200nm and above 230nm.
Far-UVC light in the 200nm to 230nm range is safe, but wavelengths below 200nm and above 230nm are not (230nm to ~350nm). It is therefore critical to use an optical filter to eliminate these harmful wavelengths and ensure safety. This is true despite spillage into the harmful UV spectrum being below Threshold Limit Values (TLVs), as shown in a study by Wood et al using an unfiltered 222nm Far-UVC handheld wand that resulted in skin damage. The importance of filtering 222nm Far-UVC was further proven by Bernard et al’s study that used Woods et al’s results to conclude that even power outputs as low as 3% in the harmful UV spectrum lead to DNA lesions; providing further evidence that filtered 222nm Far-UVC is safe but unfiltered 222nm Far-UVC is not.
All Far-UVC research on mice and humans to prove safety was done using optical filters, and therefore to replicate these safety results in real life, optical filters are necessary. UVX lamps use a proprietary filter to replicate research outcomes. In fact, recent tests on mice and humans were conducted using the same lamps and filters as UVX’s.