The UV spectrum is divided into three areas:
- UV-A, long wave, 315-400 nm
- UV-B, medium wave, 280-315 nm
- UV-C, short wave, 200-280 nm
The radiation from the UV-A "group"
is also a part of the natural sunshine on the surface of the earth. This UV-A radiation causes different photochemical processes. It has a perceptible pigmenting – but in praxis no eythematic influence.
The radiations from the UV-B "group"
shows both pigmenting and erythematic influence. They also form pre-vitamin D. This kind of radiation is mainly used in therapy.
Short waved UV-C "radiation"
has a strong germ fatal effect and also causes erythema and conjunctivitis. This kind of radiation can be made artificial when a mercury low-pressure in UV-C lamps is discharged.
Radiation with wavelengths below 200 nm form ozone.