Ultrafiolet

Ultrafiolet is the portion of the electromagnetic spectrum with wavelengths shorter than those of visible light and longer than X-rays, approximately spanning from 10 to 400 nanometers. It lies between X-rays and visible light, and its study includes both natural phenomena and engineered applications. In common classifications, ultrafiolet is divided into three main bands: UVA (about 315–400 nm), UVB (about 280–315 nm), and UVC (about 100–280 nm). Some discussions also reference far UV and vacuum ultraviolet for wavelengths outside the ranges that reach the Earth's surface.

Natural sources and artificial generation

The sun is the primary natural source of ultrafiolet radiation, though its impact at the Earth's surface is partially modulated by the atmosphere and ozone layer, which absorb shorter-wavelength components. Artificial sources include UV lamps, mercury lamps, certain types of LEDs, and other specialized light sources used in lighting, curing, disinfection, and analytical instrumentation. UV radiation is also produced in channels such as flame and arc processes.

Interactions and health effects

Ultrafiolet photons have enough energy to drive photochemical reactions, including the formation of thymine dimers in DNA, which underlies some biological effects. UVA and UVB reach the surface with differing penetrative and biological profiles: UVA penetrates deeper into the skin, UVB mainly affects the outer layers, and UVC is largely absorbed by the atmosphere and is rarely encountered outdoors. Health impacts range from vitamin D synthesis and photoprotection benefits to risks of skin cancer, aging, and eye injury with excessive exposure.

Applications and safety

Ultraviolet radiation is used for disinfection (particularly UV-C), fluorescence and spectroscopy, polymer curing, and forensic analysis. Protective measures include sunscreen that blocks UVA and UVB, sunglasses, and clothing to reduce exposure.