Exposure to ultraviolet radiation (UVR) occurs from both natural and artificial sources. The main natural source is the sun. On the other hand, artificial UVR sources are widely used in industry and also used in hospitals, Iaboratories, etc. because of their germicidal properties. They are even used for cosmetic purposes. UVR can be classified into three regions according to its wavelength : as UVA (320-400nm), UVB (320-280nm) and UVC (280-200nm). The UVC has the greatest health effect on humans among the three. The sun radiates a wide range of spectrum of electromagnetic radiation including the UVR, however the radiation below 290 nm in wavelength does hot reach the surface of the earth for effective absorption by the strato-spheric ozone layer. As a result, UVR from a natural source consists of only UVA and a part of UVB. On the other hand, artificial UVR sources include UVC region and have serious effects on the human body, especially on the skin and eyes.
