uV

Ultraviolet (UV) is a portion of the electromagnetic spectrum with wavelengths shorter than visible light but longer than X-rays, roughly 100 to 400 nanometers. It is commonly divided into three bands: UVA (315–400 nm), UVB (280–315 nm), and UVC (100–280 nm). The Earth's surface is exposed mainly to UVA and UVB; UVC is largely absorbed by the atmosphere, especially by the ozone layer.

Natural and artificial sources: The sun is the primary natural source of UV radiation. Artificial sources include tanning beds, mercury lamps, UV-C LEDs, and various curing lamps used in medical, dental, and industrial applications.

Biological effects: UV can damage biological molecules such as DNA, contributing to skin cancer, sunburn, and photoaging. UVA penetrates deeper into the skin, while UVB is more likely to cause sunburn and is strongly linked to skin cancer. UV also stimulates vitamin D synthesis in the skin, which has various health implications. UVC is the most energetic, but its surface impact is mitigated by atmospheric absorption.

Measurement and exposure: UV intensity is commonly described by a UV index, which estimates the risk of harm from unprotected sun exposure at a given time and location. Exposure is influenced by solar altitude, cloud cover, altitude, and ozone concentration.

Applications: UV radiation is used for sterilization and disinfection of water, air, and surfaces; phototherapy for certain skin conditions; curing of polymers and inks; and various analytical and forensic techniques.

Protection and safety: Protective measures include broad-spectrum sunscreens, UV-blocking clothing and sunglasses, shade, and limiting time in the sun during peak hours. Public guidance emphasizes balancing sun exposure to obtain vitamin D while reducing harmful effects.