Ultraviolet (UV) light is a type of electromagnetic radiation with wavelengths shorter than visible light but longer than X-rays, ranging approximately from 10 to 400 nanometers (nm)

. It is invisible to the human eye but can be seen by some insects like bumblebees

. UV light is subdivided into three main types based on wavelength:

• UVA (315–400 nm): Also called near UV or black light, it penetrates deep into the skin and can cause tanning and premature aging. Most UVA reaches the Earth's surface because it is not strongly absorbed by the ozone layer

• UVB (280–315 nm): Responsible for sunburn and DNA damage, UVB is mostly absorbed by the ozone layer, with only about 5% reaching the surface. It affects the outer skin layers and increases the risk of skin cancer

• UVC (100–280 nm): The most energetic and harmful type, UVC is completely absorbed by the Earth's atmosphere and does not reach the surface. It is used artificially for sterilization because of its ability to kill bacteria

UV radiation comes naturally from the Sun and constitutes about 10% of the Sun's electromagnetic output. It can also be produced artificially by electric arcs, mercury-vapor lamps, tanning lamps, and black lights

. UV light has higher energy photons than visible light, capable of inducing chemical reactions and causing fluorescence. Short-wave UV (UVB and UVC) can damage DNA and sterilize surfaces, while UVA mainly causes skin aging and tanning

. In summary, ultraviolet light is a form of invisible, high-energy electromagnetic radiation from the Sun and artificial sources, divided into UVA, UVB, and UVC bands with differing biological effects and atmospheric penetration