The mechanism of the damaging effect of ultraviolet radiation
Biological objects are able to absorb the energy of incident radiation. When a light photon interacting with a molecule, it knocks out an electron from its orbit. The result is a positively charged molecule, or a small ion, acting as a free radical. Free radicals disrupt the structure of proteins and damage the cell membrane. Since the energy of a photon is inversely proportional to the wavelength, short-wave ultraviolet radiation has more damaging to biological objects.
Damage living organisms by ultraviolet radiation always photochemical, it is not accompanied by a significant increase in temperature and may occur after a relatively long latent period. For the damage is quite low doses of radiation operating in a long time. In contrast, damage caused by infrared radiation (500-1400 nm), occurs immediately, requires simultaneous exposure to a high dose and is accompanied by an increase in tissue temperature at least 10°. Since the damage from infrared light can accumulate, prolonged or repeated mild impacts can cause the same changes, as a strong single irradiation.
The photon energy is directly proportional to its frequency, that is, inversely proportional to the wavelength: the shorter the wavelength of electromagnetic radiation, the more energy the photon has. From the entire spectrum of electromagnetic waves (cosmic rays, gamma rays, x-rays, ultraviolet radiation, visible light, infrared light, microwaves, radio waves), ultraviolet radiation consists of waves of minimum length, the energy of its photons largest of the entire optical spectrum.
To ultraviolet part of the spectrum includes wavelengths from 100 nm to 400 nm. Ultraviolet radiation with a wavelength less than 180 nm in a vacuum, so in normal conditions it is unlikely to represent a danger to human health. Photobiology emit in the ultraviolet spectrum three zones: UV-A 380 nm to 320 nm (near UV), UV-B 320 nm to 290 nm (medium UV), UV-C from 290 nm to 200 nm (far UV).