Type Wavelength
near ultraviolet 380 - 200 nm
vacuum ultraviolet 200 - 10 nm
UV-A or chemical radiation 400 - 315 nm
UV-B or Dorna radiation 315 - 280 nm
UV-C 280 - 100 nm
Sunlight consists of ultraviolet radiation for only a small 4 percent. The wavelength of
ultraviolet radiation ranges from about 10 to 380 nanometers and is sub-divided into
near- and vacuum ultraviolet. Vacuum ultraviolet is the area with wavelengths below
200 nanometers and it is to a large extent absorbed by air so that it can freely
propagate through vacuum only.
Beside this sub-division into near- and vacuum ultraviolet a sub-division into UV-A, -B
end -C is also commonly used. Ultraviolet radiation between 300 and 185
nanometers can be harmful for the human body and it may easily damage the eyes.
The ozone layer, that surrounds the earth on an altitude between 20 and 50 km,
protects us largely from this radiation. UV-radiation with wavelengths shorter than
315 nanometers (UV-B and -C) is also for a great deal blocked by glass.
There is no widely accepted standardisation of the wavelengths of the different types
of ultraviolet radiation. The table listed below is therefore an indication only. Notice
that for the ultraviolet spectrum different overlapping subdivisions exist.