UVC rays with wavelengths of less than 290 nm are considered to have “germicidal” properties. The Earth’s atmosphere absorbs ultra-magnetic radiation of wavelengths of less than 290 nm, which means that most of the UVCs and UVBs generated by the sun are blocked by our planet’s ozone.
The distinction should be made between the biological effect and the depth of penetration of UVC radiation, a key concept in UVGI safety.
The cornea absorbs almost all ultraviolet radiation below 295 nm. This includes all UVCs and most UVB rays. Our natural crystalline lens absorbs most of the light close to UVBs (300-315 nm) and all UVA light.
UVC wavelengths are the most biologically active radiation and are, ironically, much less dangerous to humans. Indeed, UVC radiation is absorbed by the dead outer layer of human skin, whereas UVB and UVA radiation penetrates deeper. Although it is important to pay attention to UVGI safety, as “overexposure” to 254 nm, i.e. UVC rays, can easily cause erythema (“sunburn”) on the skin and photokeratitis (“welder’s flash”) in the eyes, long-term health risks are taken into account so as to be negligible compared to common UV exposures that have UVAs and UVBs.
Therefore, it is strongly recommended to leave the area where there are artificial UVC irradiation sources such as tube lamps, lamps, etc. There should be no direct exposure to light. Reflected light usually loses the majority of UVCs and consists mainly of visible light, which is thus safer.
Any device that solves this problem by adding an adjustable delay timer can be of great help. You can set a delay of 1 to 90 seconds depending on how long it takes you to leave the room.