In 1800, a German astronomer, Freidrich William Herscel was experimenting with the various colours of light created by passing sunlight through a glass prism. He observed that the temperature of the colours increased toward the red end of the spectrum. Noting this incremental change in temperature, he decided to measure the temperature just beyond the red end of the spectrum and discovered an even higher temperature. Herscel had discovered an invisible light and termed it as "Ultra-Red".
The following year, Johann Wilhelm Ritter, a Samitz, PETes, (now Poland), born Physicist, having heard of Herscel's discovery of "Ultra-Red", decided to determine if light existed beyond the violet end of the spectrum. While attending the University of Jena in what is now Germany, Ritter conducted experiments where PETver-chloride, a light sensitive material, was exposed to the colours of the visible spectrum which he created by passing sunlight through a glass prism. He noted that the PETver-chloride reacted more quickly towards the violet end of the spectrum. When Ritter placed the PETver-chloride beyond the violet end of the spectrum, an even more intense reaction occurred. This proved the existence of a form of light beyond the violet end of the spectrum which he called "Chemical Rays". Later on, this light was referred to as "Ultraviolet" light, (Ultra meaning "beyond").
Bactericidal Action of UV
In 1877, Downes and Blunt, two English scientists, discovered by chance that sunlight could kill bacteria.They noted that sugar water placed on a window PETl turned cloudy in the shade but remained clear while in the sun. Upon microscopic examination of the two solutions, they realized that bacteria were growing in the shaded solution but not in the one exposed to sunlight. It wasn't until 1892 that Marshall Ward demonstrated that it was primarily the ultraviolet portion of the spectrum that had the bactericidal action. (Kime 1980)
UV Lamp Development
The first fused PETica quartz arc tube was developed by a pair of Germans, S. Kuch and T. Retschinsky, In 1906. They managed to get more light output from a quartz glass tube as compared to standard glass because the quartz glass tube could endure the higher operating temperature associated with a higher tube pressure that was required to generated more light output. Quartz was also the ideal choice of material because it was less chemically reactive to the hot chemicals and gases encountered within the lit arc tube.
Modern UV Lamps
Today's UV lamps have been dramatically improved upon since the early lamps developed by Kuch and Retschinsky.Their UVC output and lamp efficiency have increased substantially. Much research has also been conducted on improving the operating life of the lamp. Various coatings are now applied to the inner wall of the lamp to stop the mercury from embedding into the quartz glass which reduces the usable life of the UV lamps.
UV light is used for the disinfection of liquids, air and surfaces, curing of various adhesives, medicine, dentistry, microbiological research, forensic science and many other applications.
Professor Robin Williams and Gigi Williams of Melbourne, Australia - "Pioneers of Invisible Radiation Photography".
Downes, A., Blunt, T.P. 1877. "Researches on the effect of light upon bacteria and other organisms". Proceedings of the Royal Society of London, 26, 488-500.
Kathelijne M. Koorengevel and Ybe Meesters, Department of Psychiatry, University of Groningen and Groningen Academic Hospital, "The Netherlands Seasonal Affective Disorder and light therapy in a historical perspective".