ultraviolettes

Ultraviolets, or ultraviolet radiation, are electromagnetic waves with wavelengths shorter than visible violet light and longer than X-rays, roughly from 10 to 400 nanometers. The ultraviolet region is commonly divided into UVA (315–400 nm), UVB (280–315 nm), and UVC (100–280 nm). UV-C is largely absorbed by Earth's atmosphere, particularly the ozone layer, while UVA and UVB reach the surface to varying degrees and drive most of the biological effects associated with sun exposure.

Natural sources and exposure: The Sun emits copious ultraviolet radiation. Artificial sources include mercury-vapor lamps, UV LEDs, and tanning beds. UV intensity increases with altitude, latitude (closer to the equator), and during midday sun.

Health and ecological effects: Ultraviolet light can induce chemical changes in DNA and proteins. Moderate exposure aids vitamin D synthesis but excessive exposure raises risks of skin cancer, sunburn, photoaging, and cataracts. The ecological impact includes effects on phytoplankton, zooplankton, and biota that rely on UV-sensitivity for behavior or development.

Applications and safety: Ultraviolet radiation has uses in disinfection, sterilization of water and surfaces, forensic analysis, photolithography, and polymer curing. Protective measures include broad-spectrum sunscreens, protective clothing and sunglasses, and monitoring UV indices. Glass and certain filters can block UV but UVA can still penetrate ordinary glass.

History: Ultraviolet radiation was discovered in 1801 by Johann Wilhelm Ritter, who observed effects beyond the violet end of the visible spectrum and named the region ultraviolet.