The Science Behind UV-C Pathogen Reduction

How UV-C Neutralizes Pathogens

  • The germicidal ultraviolet (UV-C) bandwidth for disinfection is between 200nm and 280nm. In this range, UV-C is a powerful disinfectant that inactivates bacteria, viruses, and fungi at the genetic level. When exposed to UV-C, a pathogen’s DNA or RNA absorbs the light energy, causing structural damage that blocks its ability to replicate or function.

  • This process—rapid, residue-free, and chemical-free—stops pathogens in their tracks, making UV-C an ideal solution for fast, high-efficiency surface disinfection. Although UV-C is extremely effective in killing pathogens, direct contact is harmful to human eyes and skin.

  • Surface disinfection efficacy is directly related to the cumulative UV-C dosage delivered to the intended target. This is the amount of energy, in Joules (J), impacting a known surface area, in square centimeters (cm2). The equation for UV-C dosage is: 

UV-C Dose (J/cm²) = UV-C Intensity (W/cm²) × Exposure Time (seconds)

  • Intensity is most influenced by the UV-C source wavelength, distance from UV-C emitter to the intended target, and the angle at which the UV-C rays impact the target.

 

UV-C Disinfection Efficacy Factors

Emitter design plays a critical role in maximizing intensity—specifically through wavelength, distance to target, and incident angle. Recognizing these factors is key to improving overall disinfection performance.

Emitter Wavelength

  • Emitter wavelength plays a significant role in pathogen disinfection effectiveness. The wavelength most easily absorbed by nucleic acids, and therefore the most effective at inactivating a wide range of DNA, is 265 nm.

  • UV-C emitters are available in Low Pressure Mercury (LPHg), Medium Pressure Mercury (MPHg), and LED formats. While LPHg and MPHg sources exhibit narrow spectral power distributions (SPDs), UV-C LEDs offer broader SPDs, enhancing overall disinfection effectiveness.

  • LPHg bulbs often standardize on an emitted peak wavelength of 253.7 nm, whereas UV-C LEDs are available in various peak wavelengths—including 222 nm, 265 nm, and 285 nm—allowing for tailored spectral targeting based on microbial susceptibility.

  • The reduction in E. coli varies significantly between peak wavelengths. Comparative testing shows a substantial difference in log and percentage reduction between a 254 nm UV lamp and a 266 nm LED at equivalent dosages, as illustrated in the table and bar chart below.

 
 

Emitter Distance

  • Emitter-to-surface distance significantly affects UV-C disinfection efficacy. According to the Inverse Square Law, radiation intensity decreases proportionally to the square of the distance from the source.

  • Therefore, doubling the distance between the emitter and target surface reduces UV-C intensity to one-fourth. This substantially diminishes the delivered dosage and overall disinfection performance.


Angle of Incidence

  • Similarly, the angle of the UV-C light upon the intended target directly impacts disinfection effectiveness.

  • Maximum intensity and the greatest germicidal effect occurs when UV-C light strikes a surface perpendicularly, or at 0°.

  • As the angle of incidence increases, the germicidal effectiveness decreases. This is because the same amount of UV-C energy is distributed over a larger surface area, reducing the intensity per unit area.