The ultraviolet spectrum is a part of the electromagnetic spectrum that lies between visible light and X-rays. It consists of wavelengths ranging from about 10 nanometers to 400 nanometers. Ultraviolet (UV) light is not visible to the human eye but can have significant effects on living organisms, including skin damage and vitamin D production in humans. Ultraviolet light is divided into three categories: UVA, UVB, and UVC. UVA rays have the longest wavelengths and can penetrate deep into the skin, while UVB rays are responsible for sunburns. UVC rays are the most harmful but are mostly absorbed by the Earth's atmosphere, preventing them from reaching the surface.