Optical radiation

Rays differ in their frequency. Radio waves, for example, are very long-wave, while optical beams belong to the short-wave range. The frequency range of UV radiation covers only a very small part of the electromagnetic spectrum.

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Ultraviolet rays (UV) are short-wave energies that can be divided into three areas: UV-A (long wave 400 – 315 nm), UV-B (medium wave 315 – 280 nm), UV-C (short-wave 280 – 100 nm).


The long-wave UVA rays cause various photochemical processes, have a short-term pigment-forming effect (sun tan) and can cause indirect DNA damage and melanoma. UVA rays penetrate glass and transparent plastics. UV-A light is closest to visible, violet light and is colloquially known as black light. It is less energetic and is used in the curing of photopolymers, in photochemistry and also in reprography. UV-A light is also used for insect control.


Medium-wave UVB rays are more energetic than UVA rays and have a delayed pigment-forming effect, which manifests itself in increased melanin production (sunburn).
UVB is also responsible for the formation of previtamin D in the human body. This radiation is used for therapeutic purposes, among others. Even normal window glass is no longer permeable for UV-B and shorter UV rays.


UVC rays are shorter-wave and more energetic than UVA and UVB rays. They cover most of the entire UV range and have a strong germicidal effect in the 253.7 nm range. Like the visible wavelengths of light, UVC rays only travel in a straight line and their intensity decreases with increasing distance from the source. UV-C light is used to disinfect medical equipment, but also air, water and food. UV-C light kills viruses, germs and bacteria and should be harmless to humans when used correctly.

Dose and effect

The effectiveness of UV-C in the inactivation of micro-organisms is always directly related to the UV dose applied.

As a general rule, the simpler the structure of a micro-organism, the easier it is to inactivate by means of UV radiation. This is why viruses, bacteria and bacterial spores are generally much easier to destroy than complex micro-organisms such as yeasts and vegetative fungal cells (eukaryotic cells). Fungal spores, whose DNA is also protected by a pigmented cell wall and a concentrated cytoplasm, can only be inactivated by applying substantial doses of UV radiation.

To ensure thorough disinfection, intensive UV light is required. The smaller the distance to the surface to be treated, the more effective the process.

No formation of resistance

An important advantage of physical UV disinfection is that it does not cause the formation of resistance.

UVC disinfection also works when germs have already acquired resistance to conventional disinfection measures such as alcohol or antibiotics. UV disinfection works for all micro-organisms, whether they are common Escherichia Coli bacteria, SARS, Legionella or mould. A sufficient UVC dose, many years of application know-how and the necessary UV equipment technology are the prerequisites for the desired success. The number of scientific proofs of UV disinfection has been growing steadily in recent years.