The development of UVGI traces back to 1878 when Arthur Downes and Thomas Blunt found that sunlight, particularly its shorter wavelengths, hindered microbial growth. Expanding upon this work, Émile Duclaux, in 1885, identified variations in sunlight sensitivity among different bacterial species. A few years later, in 1890, Robert Koch demonstrated the lethal effect of sunlight on Mycobacterium tuberculosis, hinting at UVGI's potential for combating diseases like tuberculosis.
Subsequent studies further defined the wavelengths most efficient for germicidal inactivation. In 1892, it was noted that the UV segment of sunlight had the most potent bactericidal effect. Research conducted in the early 1890s demonstrated the superior germicidal efficacy of UV-C compared to UV-A and UV-B.
The mutagenic effects of UV were first unveiled in a 1914 study that observed metabolic changes in Bacillus anthracis upon exposure to sublethal doses of UV. Frederick Gates, in the late 1920s, offered the first quantitative bactericidal action spectra for Staphylococcus aureus and Bacillus coli, noting peak effectiveness at 265 nm. This matched the absorption spectrum of nucleic acids, hinting at DNA damage as the key factor in bacterial inactivation. This understanding was solidified by the 1960s through research demonstrating the ability of UV-C to form thymine dimers, leading to microbial inactivation. These early findings collectively laid the groundwork for modern UVGI as a disinfection tool.