Ultraviolet is at wavelengths between about 100 nm and 380 nm, which corresponds to a frequency range between 30 PHz (petahertz) and 789 THz(terahertz). According to DIN 5031, the UV range is divided into three wavelength ranges, designated UV-A, UV-B and UV-C, to which different wavelengths are assigned.
For example, the UV radiation of UV-A, which is relatively rich in sunlight, is between 315 nm and 380 nm and causes tanning of the skin. UV-A radiation is considered harmless. UV-B with wavelengths between 280 nm and 315 nm reaches the earth's surface and is more energetic than UV-A. UV-C, with wavelengths between 100 nm and 280 nm, is the shortest-wave UV light and is absorbed in the earth's atmosphere. Radiation in the UV-C wavelength range cannot be perceived by humans. However, this short-wave radiation can destroy molecular chains and thus genetic material and is therefore harmful to humans. On the other hand, UV-C light can be used to kill viruses and bacteria.
In addition to the ultraviolet discussed here, there is also extreme ultraviolet light( EUV), which has wavelengths between 10 nm and 100 nm and is used in semiconductor lithography to increase integration density.