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 ("On the influence of light upon protoplasm", Proc. Roy. Soc. 28, 199-213, 1878). Much later it was recognised that there is a specific wavelength dependency with a reaction maximum in the area of 250 to 270nm, which is in the shortwave frequency band of C type waves (UVC - rays).

The exact explanation for this phenomenon took a very long time to explain and was only unravelled with the discovery and later on research of the DNA (Deoxyribonucleic Acid) in the 60ies.