Ultraviolet radiation (UV, ultraviolet)
Is an electromagnetic radiation invisible to the human eye, with a wavelength in the range of from 100 to 400 nm. Discovered in 1801, it is able to trigger photochemical reactions in numerous materials and organisms. If a living organism or a material is exposed to the ultraviolet radiation in small doses, caused photochemical reactions may have a positive effect on them. UV radiation triggers vitamin D production. Ultraviolet radiation ma be divided into the following, considering their influence on living organisms:
Wavelength in the range of 315 – 400 nm. They constitute 95% of all UV radiation accessing the Earth. It is not stopped by clouds, window panes, or car windows; whether sitting in the car or a sun-exposed room, or in a cloudy day in summer or winter, we are exposed to the same amount of UVA. Having longer wave, UV-A rays penetrate skin to its deep layers, even to the dermis.
Wavelength in the range of 280 – 315 nm. They constitute 5% of all UV radiation accessing the Earth. It is filtrated by clouds and window panes. As its wavelengths are shorter, they do not penetrate the skin very deep, only to the epidermis. It is responsible for the instances of erythema and skin burns, as, despite their shorter length, their energy is much higher than that of UVA.
Wavelength in the range of 100 – 280 nm. Thanks to the high energy level of photons, absorption of this radiation by a substance may visibly influence its physical and chemical characteristics. UV-C may cause photoluminescence, photoelectric phenomena, photochemical reactions (oxidation, reduction, decomposition, polymerisation). It is characterised by high biological activity. UV-C is lethal for vegetative and endospore forms of microorganisms, as well as for viruses. Its biocidal influence on microorganisms is caused when the radiation is transmitted inside the cells and damages organism's DNA and cellular proteins, which often perform crucial functions in metabolism. As a result, the cell dies. Ultraviolet radiation with its bactericidal functions are also able to mutate, inactivate specific sera and bacterial toxins.
UV-C radiation was used to disinfect water and machinery already in the 19th century. The first water disinfection system was made in 1909. UV was first used for air disinfection in 1930s. The first air-string UV disinfection guidelines were written already in 1940s.
Thanks to the use of UV-C, disinfection:
- is not hazardous for the users of the rooms;
- is safe for the environment;
- is performed without using chemicals and high temperature;
- may be performed 24 h a day, 7 days a week.
As of now, exposure to ultraviolet radiation is the most commonly used physical disinfection method.