Ultraviolet rays are the invisible electromagnetic radiation placed in spectrum area between visible spectrum and roentgen radiation. Wave-length of the radiation lies in the range of 100-400 nano meters.
Ultraviolet spectrum is divided into three sub-bands:
UV-A - long wave-band (315 - 400 nano meters)
UV-B-medium (middle) wave band (280 - 315 nano meters)
UV –C ...