Ultraviolet is the name given to electromagnetic radiations with wave lenghts between 100 and 400, situated between the visible spectrum and x-rays. Ultraviolet rays are invisible and are commonly classified in three conventional bands:
- UV-A radiations (long waves) from 315 to 400nm.
- UV-B radiations (medium waves) from 280 to 315nm.
- UV-C radiations (short waves) from 100 to 280 nm.
(one nanometer corresponds to a millionth of a milimeter).
The most efficient artificial source of hight intensity UV-C rays are lamps which discharge mercury vapor at low pressure, and can supply homogeneous monochromatic radiation at 250-265 nm wave lenght.
The fundamental UV-C radiation with the maximum germicidal effect is represented by the 254 nm spectral line (the point at which nucleic acids of micro-organisms have their maximum absorption)
The need for limiting the presence of pathogenic germs in the air has brought about increasing interest in the use of the short UV-C band of UV rays. UV-C ultraviolet rays are bactericidal by their physical nature.
They act by producing the denaturation of the proteins in the bacteria or the breakage of cell ways through mechanical action, provoking the death of the micro-organism (destruction of the DNA).
The case against this positive reduction of bacteria is the considerable danger of these rays which, if they come into contact with the skin and eyes, can cause rashes and conjunctivitis. For this reason, normal lamps which exploit UV-C rays can be kept in operation only in the absence of persons, with the obvious reduction of their effectiveness over a period of time.