Sterilization Technology Using an Ultraviolet-radiation Source

Abstract

1. About UV-radiation sterilization Ultraviolet (UV) radiation is classified according to its wavelength as UV-A (wavelength: 315–400 nm), UV-B (280–315 nm), and UV-C (100–280 nm). UV-C, which is the UV radiation contained in sunlight, is absorbed by the ozone layer. UV-A and UV-B, which reach the surface of the earth, cause sunburn, but their sterilization effect is low. UV-C (with short wavelength) imparts high energy per photon, and it can be efficiently absorbed by the DNA and RNA possessed by bacteria and viruses and thereby destroy the genetic information held by the DNA, suppress cell division and proliferation, and sterilize things (i.e., inactivate microorganisms). The maximum absorption of UV by DNA is around the wavelength of 260 nm. Accordingly, as for the light source for UV sterilization, two kinds of lamps are widely used: (i) low-pressure mercury lamps (which efficiently emit the 254-nm bright line of mercury) and (ii) mediumand high-pressure mercury lamps, which have lower luminous efficiency but higher radiation density that low-pressure mercury lamps and generate broad light emission around 260 nm. In recent years, LEDs in the deep-ultraviolet radiation region have also been developed, and they are expected to be a “mercury-free” light source in the future. In this article, the usefulness of such UV-radiation sterilization, including the features and practical examples of various UV-radiation light sources, is explained.