Ultra Violet light
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency of approximately 30 PHz) to 400 nm (750 THz), shorter than that of visible light but longer than X-rays. UV radiation is present in sunlight, and constitutes about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.
There are 3 kinds of UV light depending on the wavelength : UVA, UVB and UVC. UVA is the closest to the visible light. It fades colors in plastics and clothes and contributes to smog. UVB (315-290) is mostly absorbed by the ozone laqyer in the atmosphere but the ammount that makes it through can damage the DNA molecules in living cells and cause sunburn. UVC is very dangerous but it is all blocked by the earth’s atmosphere.