UV Lights & Germ Prevention

Certain wavelengths of UV are more effective in destroying microorganisms.

Ultraviolet light is electromagnetic radiation with a wavelength longer than x-rays but shorter than visible light. UV light is sometimes used for disinfection and sterilization, although certain wavelengths are more effective for this application than others.

Effects

UV harms microorganisms by damaging their genetic material -- typically DNA but also RNA in the case of many viruses. Bacteria and fungi can repair DNA damage up to a certain limited extent, but enough damage will make it impossible for the cell to reproduce. UV with wavelengths in the 250 to 270 nanometer range is best, since DNA absorbs more UV at these wavelengths. Not all species and strains of bacteria and viruses are equally susceptible, although viruses are typically more vulnerable than bacteria.

Function

A UV light works by passing an electric current through mercury vapor in a glass tube. The current energizes or excites some of the electrons in the mercury atoms. These electrons then fall back down to a lower orbital, releasing energy in the form of electromagnetic radiation as they do so. UV disinfection systems are one popular approach to disinfecting treated effluent; germicidal UV lamps help disinfect circulating air in some hospitals and health care environments.

Considerations

It's important to remember that UV light is dangerous to humans also. Exposure to high intensity can damage human eyes, and long-term exposure can increase the risk of skin cancer. UV sterilization or disinfection systems should always be designed in such a manner that humans are not directly exposed to the radiation.

References

• Environmental Health Perspectives: The Characterization of Upper-Room Ultraviolet Germicidal Irradiation in Inactivating Airborne Microorganisms
• National Drinking Water Clearinghouse: UV Disinfection
• PennState Department of Architectural Engineering: Ultraviolet Germicidal Irradiation
• EPA: Ultraviolet Disinfection