ultravioletten

Ultraviolette licht, in English often called ultraviolet light, refers to electromagnetic radiation with wavelengths shorter than visible light and longer than X-rays, roughly 10 to 400 nanometers. The ultraviolet region is commonly divided into UVA (about 315–400 nm), UVB (280–315 nm), and UVC (100–280 nm).

Most UVC and much of UVB are absorbed by the Earth's atmosphere, particularly the ozone layer, so only UVA and a portion of UVB reach the surface. The sun is the primary natural source, while artificial sources such as mercury lamps, UV LEDs, welding arcs, and black lights provide additional ultraviolet illumination for specific applications.

Biological effects of ultraviolet radiation are significant. UV exposure can cause skin sunburn, photoaging, and increases the risk of skin cancer, but it also enables vitamin D synthesis in the skin. Prolonged or unprotected exposure can damage eyes and may affect immune function. Because different wavelengths interact with materials differently, UV is also used to study fluorescence, reactions, and spectra.

Uses and applications include disinfection and sterilization with UV-C, curing of inks and polymers, forensic analysis, fluorescence photography, and UV astronomy, where shorter-wavelength radiation reveals information about hot stars and interstellar matter. Protective measures are important in contexts involving UV sources: broad-spectrum sunscreen, protective clothing, and UV-blocking eyewear reduce risk, as does limiting exposure during peak hours and using shielding when appropriate.

History notes: Johann Wilhelm Ritter demonstrated ultraviolet radiation in 1801 by observing effects beyond violet light, and the term ultraviolet was coined to describe this region of the spectrum.