Q：How to divide the wavelength bands of UV light?
A: The main source of UV light in nature is the sun. All species in the ecological system of the earth are under the influence of UV radiation from the sun. Based on biological influence, UV light is usually divided into three sub-bands: UVA, defined by wavelength between 400 and 320 nm, can penetrate through clouds and glasses, into rooms and cars, and into the dermis of skin, which can cause sunburns and is the main cause of skin aging and wrinkles. UVB, defined by wavelength between 320 and 280 nm, can promote the synthesis of Vitamin D in skin, but can also lead to sunburns and skin swelling, having the strongest carcinogenicity. UVC, defined by wavelength between 280 and 200 nm, would be completely absorbed by the ozone sphere before it can reach the ground. UVC has a strong destructive effect on the DNA of bacteria and virus, which is the main wavelength band used by UV disinfection lamps. Besides, UV radiation with wavelength less than 200 nm would be strongly absorbed by air, and that's why it is called vacuum UV light.