The Electromagnetic (EM) Spectrum is simply a name scientists use when referring to the entire range of radiation types. Radiation is energy that travels and spreads out as it moves. Examples include visible light and radio waves. Other examples of EM radiation are ultraviolet and infrared light, microwaves, X-rays and gamma-rays.
Ultraviolet radiation is that part of the electromagnetic spectrum between visible light and x-rays. Ultraviolet, or UV light, is divided into three regions, based on wavelength. UVA, (know as longwave or blacklight), is radiation with wavelengths between 315nm and 400nm. UVB ( midrange) spans wavelengths from 280 to 315nm and UVC (shortwave) covers 280nm down to about 30nm.
Shorter wavelengths of light are more energetic than longer wavelengths. Unlike x-rays, UV radiation has a low power of penetration, with effects on the body limited to skin and eyes. Direct and indirect exposure to UV, especially in the UVB and UVC range, include sunburn, aging and carcinogenic changes. UV protective eyewear, clothing and creams are recommended whenever exposure to UV is possible.
An interesting characteristic of UV radiation occurs when it falls upon certain substances know as phosphors (phosphorescent substance), where it causes the phosphors to emit specific visible radiation which is known as fluorescence. A similar effect is phosphorescence in which the emission lasts longer after the UV source is removed. Many practical applications have been developed that take advantage of these unique properties triggered by UV light.