What is the germicidal spectrum of ultraviolet light for killing microorganisms?

What is the germicidal spectrum of ultraviolet light for killing microorganisms?

• A. 50-90 nanometers
• B. 100-180 nanometers
• C. 200-280 nanometers
• D. 300-350 nanometers

Answer: (C)

Ultraviolet germicidal effectiveness comes from the UV-C portion of the spectrum, about 200 to 280 nanometers. In this window, DNA and RNA absorb UV light strongly, forming pyrimidine dimers (especially thymine dimers) that block replication and transcription, so the microorganisms cannot reproduce and are inactivated. This is why UV disinfection sources used in labs and clinics are designed to emit around 254 nanometers, a typical UV-C wavelength produced by common low-pressure mercury lamps. Wavelengths outside this range are much less effective in typical disinfection scenarios because longer wavelengths (UV-A) absorb less by nucleic acids and can penetrate differently, and very short (vacuum) UV is blocked by air and not practical for surfaces or water. So the germicidal spectrum for killing microorganisms sits in the 200–280 nanometer range.

Ultraviolet germicidal effectiveness comes from the UV-C portion of the spectrum, about 200 to 280 nanometers. In this window, DNA and RNA absorb UV light strongly, forming pyrimidine dimers (especially thymine dimers) that block replication and transcription, so the microorganisms cannot reproduce and are inactivated. This is why UV disinfection sources used in labs and clinics are designed to emit around 254 nanometers, a typical UV-C wavelength produced by common low-pressure mercury lamps. Wavelengths outside this range are much less effective in typical disinfection scenarios because longer wavelengths (UV-A) absorb less by nucleic acids and can penetrate differently, and very short (vacuum) UV is blocked by air and not practical for surfaces or water. So the germicidal spectrum for killing microorganisms sits in the 200–280 nanometer range.