Visual radiation

Of the radiation energy to which we are exposed on a daily base, we are only aware of a small part as light or warmth. The far greater part of this electromagnetic energy, however, remains unnoticed. This also includes ultraviolet radiation.

The energies can also be explained with a wavelength model. Radiation differs through frequency, for example, radio waves are of long wavelength, while visual radiation is in the short wave range. The frequency range of UV radiation only includes a very small part of the electromagnetic range.

UV radiation

Ultraviolet radiation (UV) is a type of short wave energy and beside visible light and infrared rays is in the group of optical radiation. It is therefore possible to bend, deflect, refract and reflect this radiation.

The term ‘ultraviolet’ (in the sense of ‘beyond violet’) is based on the fact that the UV range with the shortest wavelength starts with those wavelengths that the human eye sees as blue-violet colour.  Due to this fact UV rays are invisible for the human eye.

UV radiation is divided into three areas:

UV-A (long wavelength):
UV-B (medium wavelength):
UV-C (short wavelength):
400 - 315 nm
315 - 280 nm
280 - 200 nm

 

Arten von UV-Strahlung: UVA, UVB, UVC - Schaubild

Which types of radiation are germicidal?

Healing powers have been attributed to the sun since ancient times. The scientists Arthur Downes and Thomas P. Blunt discovered as far back as 1878, that micro-organisms do not reproduce when exposed to direct sunlight.

After this discovery, it took some time before the correlation between a specific wavelength and the maximum reaction was recognised at 250 to 270 nm, being part of the UV-radiation from the short wave C range (UV-C). 

Since the Fifties of the last century, with the discovery of the structure of DNA as a double helix by the researchers James Watson and Francis Crick, the secret of this explanation was found. 

Why does UV-C radiation have disinfecting properties?

Connection between dosage and effect

The effectiveness of a disinfection method based on UV-C radiation is directly connected to the dosage used (= duration x energy / surface). High intensity during a short duration, or low intensity over a long time period are practically interchangeable and almost have the same disinfecting effects. The dosage as an important element is demonstrated as µW*s/cm², and frequently also in J/m². 

As a rule, the following applies: the simpler a microorganism is formed, the easier it can be inactivated by UV radiation. This is why viruses or bacteria (procaryotic cells) in general can be much more easily destroyed than complex microorganisms such as yeasts and vegetative fungi (eucaryotic cells). Especially mould spores, which have a DNA that is protected through a pigmented cell wall and concentrated cytoplasm, do need a huge amount of UV energy to be combated in this manner.

Effect on humans

Wirkung von UV-Strahlung auf den menschlichen Körper

Harmless use of UV-C

UV-C-radiation does not permeate solid bodies - even no window glass (borosilicate, duran) or transparent plastics (acrylic glass, polystyrene, etc.).

As with the visible wavelengths of light, UV-C radiation only moves in a direct line and decreases in intensity by increasing distance to the source. Consequently, the further the distance towards the UV source the less dangerous it is. Equipment with protective slats or fully enclosing vessels therefore never can be hazardous. 

If protracted direct eye or skin contact with a freely emitting UV source is unavoidable, simple precautions such as protective glasses or suntan cream with a high protection factor are sufficient.  

Do you have questions?

Contact our specialist advisors today:

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