Like electricity, ultraviolet light is as old as the universe. It just took someone to notice. In 1877, British Physiologist Arthur Downes and scientist Thomas P. Blunt noticed. They put solution-filled test tubes outside and discovered that sunlight could kill and inhibit the development of pathogenic bacteria.
Some 25 years later, the German Ophthalmologist Ernst Hertel built on this knowledge, determining that light in the UV-C wavelength, rather than UV-A or UV-B, is the most effective for killing microorganisms. Around the same time, the Danish Professor Niels Finsen won the Nobel Prize for Physiology in recognition of his work in treating lupus vulgaris bacteria on human skin with concentrated light (See image). In the 1930s and 1940s, William F. Wells, a Harvard University sanitary engineer, made a significant stride in the knowledge and application of UV-C light for disinfection by proving its effectiveness in killing airborne microorganisms. It was Wells who discovered that bacteria and viruses can be transmitted to people through the air they breathe.
UV has been proven effective against a broad spectrum of microorganisms. Viruses contain RNA or DNA and are thus susceptible to irradiation. Bacteria and fungi both contain DNA and are similarly vulnerable to UV light. Spores are also susceptible to UV. With the longstanding use of UV for disinfection, there is a plethora of information regarding dosages necessary to inactivate different microorganisms. Bacteria are generally easier to inactivate than viruses, with fungi and spores being even harder to inactivate with UV. (Read the paper)
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