Ultraviolet Radiations : The ultraviolet (UV) light has higher energy than visible light. Hydrogen lamps, deuterium lamps and other sources of ultra-violet are used for a variety of purposes in physical, chemical and biological laboratories. These applications include spectroscopy. The sterilisation of instruments, the initiation of chemical reactions and the detection of purines and other substances which fluoresce when irradiated with UV light in chromatography and other separation techniques. Ultraviolet sources may be recognised by their intense pale blue illumination, for example mercury vapour lamps and high voltage sparks and arc emitted at the time of welding.