Pulsed UV‐C Disinfection of Escherichia coli With Light‐Emitting Diodes, Emitted at Various Repetition Rates and Duty Cycles

Abstract

A 2010 study exposed Staphylococcus aureus to ultraviolet (UV) radiation and thermal heating from pulsed xenon flash lamps. The results suggested that disinfection could be caused not only by photochemical changes from UV radiation, but also by photophysical stress damage caused by the disturbance from incoming pulses. The study called for more research in this area. The recent advances in light‐emitting diode (LED) technology include the development of LEDs that emit in narrow bands in the ultraviolet‐C (UV‐C) range (100–280 nm), which is highly effective for UV disinfection of organisms. Further, LEDs would use less power, and allow more flexibility than other sources of UV energy in that the user may select various pulse repetition frequencies (PRFs), pulse irradiances, pulse widths, duty cycles and types of waveform output (e.g. square waves, sine waves, triangular waves, etc.). Our study exposed Escherichia coli samples to square pulses of 272 nm radiation at various PRFs and duty cycles. A statistically significant correlation was found between E. coli’s disinfection sensitivity and these parameters. Although our sample size was small, these results show promise and are worthy of further investigation. Comparisons are also made with pulsed disinfection by LEDs emitting at 365 nm, and pulsed disinfection by xenon flash lamps.

Efficacy of Pulsed 405-nm Light-Emitting Diodes for Antimicrobial Photodynamic Inactivation: Effects of Intensity, Frequency, and Duty Cycle

“…In a study by Wengraitis et al, 20 Escherichia coli biofilms exposed using UV-C LEDs showed a change in sensitivity with duty cycle. Results showed a fourfold increase in sensitivity as the duty cycle dropped from 90% to 10%, suggesting a strong correlation between duty cycle and bacterial inactivation.…”

“…Results showed a fourfold increase in sensitivity as the duty cycle dropped from 90% to 10%, suggesting a strong correlation between duty cycle and bacterial inactivation. 20 …”

“…In these UV studies, 19,20 the exposure time, rather than the peak intensity, was altered to keep the dose constant. The longer exposure times could possibly have resulted in increased inactivation through the action of radicals generated in the bacterial suspensions.…”

“…A study using UV-C LEDs 20 compared different duty cycles and frequencies, but the exposure time rather than the peak intensity of the light was varied to keep the dose constant. Varying frequencies in the range 0.5–100 Hz were found to have an effect on inactivation, but there was no clear trend showing whether higher or lower frequencies were more or less effective for the various regimes.…”

“…Pulsed operation of UV light-emitting diodes (LEDs) has reportedly resulted in improved antimicrobial efficacy 19,20 ; therefore, it is of interest to investigate whether the same principle can be applied to 405-nm light.…”