The Discovery of UV Light

Ultraviolet radiation, commonly called ultraviolet light, is invisible radiation with a wavelength shorter than the wavelength of the light visible to humans and longer than x-ray radiation.

UV-C radiation was discovered in 1801 by the German physicist Johann Wilhelm Ritter on the basis of silver salts turning black in sunlight. In 1878, the scientists Downes and Blunt discovered that microorganisms are significantly reduced when exposed to sunlight. Subsequent research proved that the invisible part of the sun’s radiation, with a wavelength under 320 nm, has a germicidal effect.

UV Light Spectra and Their Names

Ultraviolet radiation is not visible to the human eye and contains the following parts of the spectrum according to DIN 5031-7:

Long-Wave (black light)UV-A (380 - 315 nm)
Medium-Wave UV (Dorn radiation)UV-B (315 - 280 nm)
Short-Wave UVUV-C (280 - 200 nm)
Vacuum UVUV-C (200 - 100 nm)
Extreme UVEUV (121 - 10 nm)

UV radiation with a wavelength under 300 nm is used to kill microorganisms on account of its having a high density of energy. UV-C light’s highly dense energy causes a corresponding reaction in microorganisms. After this amount, at a wavelength of 254 nm, bacteria, fungi, molds, and virus are killed or damaged, depending on the dose of radiation, by having their DNA destroyed and further cell division is halted.

Below 200 nm, radiation has waves that are so short and so powerful they are absorbed by oxygen (02), which results in it being split into two oxygen radicals (2O). Both of these oxygen radicals always subsequently react with one other oxygen molecule (O2), and ozone is created (O3).

Illustration: The Light Spectrum

UV-C Radiation Doses for Sterilization

Empirical studies have proven that the reduction of germs goes hand in hand with radiation’s duration and intensity. This factor is expressed as the product of mW x s/cm2 (radiation intensity x radiation duration per cm2).

In the following depiction of various microorganisms, we can see that it is possible to kill those showing higher sensitivity to UV-C radiation using a low dose (E. coli bacteria), whereas, for example, influenza viruses can only be made inactive using high-energy radiation. The table further shows that the requirements for germ elimination ultimately determine the UV dose (e.g., from 90% up to 99.99%). For germs occurring during food processing, it has been shown that higher doses are necessary for yeasts, molds, and spores. The same applies for inactivating microorganisms in the medical field.

Inactivating 99.9 % of germs:

BACTERIA (mW/cm2 x s)

Bacillus anthracis 13,7Pseudomonas aeruginosa 16,5
B. Megatherium sp. (veg.) 3,4Pseudomonas fluorescens 10,5
B. Megatherium sp. (spores) 8,0S. typhitmurium 24,0
B. paratyphosus 9,6Sarema lutea 59,0
B. subtilis (spores) 36,0Seratia marcescens 7,2
Corynebacterium diphteriae 10,0Shigella paradysenteriae 5,2
Eberthella typosa 6,3Spirillum rubrum 13,0
Escherichlia coli 9,0Staphylococcus albus 5,4
Micrococcus candidus 19,0Staphylococcus aureus 7,8
Micrococcus sphaeroides 30,0Staphylococcus hemolyticus 6,6
Neisseria catarrhalis 13,0Staphylococcus lactis 18,0
Phytomonas tumefaciens 13,0Staphylococcus viridans 6,0

YEASTS (mW/cm2 x s) FUNGI (mW/cm2 x s)

Saccharomyces ellipsoidens 18,0Penicillium roqueforti (green) 39,0
Saccharomyces sp. 24,0Penicillium expansum (olive) 39,0
Saccharomyces cerevisiae 18,0Penicillium digitatum (olive) 132,0
Brewing yeast 9,9Aspergillus glaucus (blue-green) 132,0
Baking yeast 11,7Aspergillus flavus ( yellowish) 180,0
Aspergillus niger (black) 396,0
Rhisopus nigricans (black) 330,0
Mucer racemosus A (light grey) 51,0
Mucer racemosus B (light grey) 51,0
Oospera lactis (white) 15,0

Various factors such as air temperature, humidity, and air speed must be taken into consideration when specifying the dose UV-C for sterilization. This model is based on many years of experience, the opportunity to measure microorganism levels on site, and subsequent work on further developing UV-C technology. Currently, this technology has made it possible to offer plug-in systems for ozone disinfection that include ozone controls and gauges – in addition to UV-C sterilization systems.

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