Ultraviolet light is a type of electromagnetic radiation, which comes from the sun, is invisible to the human eye. It makes black-light posters glow, and is responsible for sunburns. However, exposure to UV radiation is damaging to living tissue. 

Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic (EM) spectrum. The spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.