ultraviolet

Ultraviolet radiation is electromagnetic radiation with wavelengths shorter than visible light and longer than X-rays, roughly spanning 10 to 400 nanometers. It is commonly divided into UVA (315–400 nm), UVB (280–315 nm), and UVC (100–280 nm), with the vacuum ultraviolet (about 100–200 nm) being unable to propagate in Earth’s atmosphere. The boundary definitions vary, but these categories are widely used in science and industry.

Most UV reaching Earth originates from the Sun, yet the atmosphere absorbs much of it. UVC is almost completely blocked by the ozone layer and air, while UVA and part of UVB reach the surface. Artificial sources include mercury-vapor and metal-halide lamps, UV-C lamps used for disinfection, and LEDs emitting in the UV range.

Applications of ultraviolet radiation are diverse. UV is used for disinfection and sterilization of water and surfaces, polymer curing and ink drying, and in forensic and biochemical analysis. UV light also drives fluorescence, enabling spectroscopy and imaging. In astronomy, ultraviolet observations from space avoid atmospheric absorption and reveal phenomena not visible in other bands.

Biological effects depend on wavelength and exposure duration. UV exposure can damage DNA, cause sunburn, cataracts, and skin aging, and elevates cancer risk. Conversely, UVB exposure can stimulate vitamin D production in the skin. Protective measures—sunscreen, protective clothing, and eyewear—are advised when exposure is frequent or intense.