The formal discovery that specific monochromatic wavelengths of UV light are bactericidal was made as early as 1928 (3). Since then UV lamps have been continuously developed and commercialized for a variety of sanitization and sterilization applications. The most common commercial sources of monochromatic UV light are continuous wave low and medium pressure mercury vapor arc lamps. Low pressure lamps are electrically efficient UV sources, but they are inherently low power devices (10’s of watts) suitable for a very limited range of disinfection uses, are not capable of complete microbial sterilization, do not inactivate cellular repair processes, and are difficult to control in inline processes due to high output variability. Medium pressure lamps are more powerful (100’s of watts), produce a wider UV spectrum, and generate sterilization levels of UV irradiance. They are constrained to an extremely limited application range, however, due to their very high operating temperatures (400 ºC – 1000 ºC), non-uniform output behavior, low electrical efficiency, and high cost (4). Finally, the extreme toxicity of mercury vapor poses a serious safety threat.
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