Electromagnetic radiation invisible to humans with wavelengths shorter than "normal" and visible light and beyond the violet. Ultraviolet radiation causes chemical reactions in many substances. It is also involved in the formation of ozone in the atmosphere. In living organisms, prolonged exposure can lead to harmful changes and mutations. Due to its physical and biological properties, UV radiation is further subdivided into UV-A radiation (wavelength 400 - 315 nm), UV-B radiation (315 - 280 nm) and UV-C radiation (280 - 100 nm). UV-A radiation directly adjoins visible light. UV-C radiation borders directly on the range of ionising radiation. The shorter the wavelength, the more energetic the radiation and the more damaging it is. The Italian pomologist Alberto Piròvano (1884-1973) experimented with irradiating grapevine cultivation material with UV light as early as 1912 in order to deliberately induce changes in the cell material.