Efficacy of Pulsed 405-nm LEDs for antimicrobial photodynamic inactivation: effects of intensity, frequency, and duty cycle

Objective: This study investigates possible advantages in pulsed over continuous 405-nm LED-light for bacterial inactivation and energy efficiency.
Background: Alternative non-antibiotic methods of disinfection and infection control have become of significant interest. Recent studies have demonstrated the application of systems using 405-nm light-emitting diodes for continuous disinfection of the clinical environment, and also for potential treatment of contaminated wounds.
Methods: Liquid suspensions of 10³ CFU/ml populations of Staphylococcus aureus were subject to pulsed 405-nm light of different frequencies, duty cycles and intensities, and for different lengths of time.
Results: Pulsed exposures with the same average irradiance of 16 mWcm² and varying duty cycle (25%, 50%, 75%), showed very similar performance compared with continuous exposures, with 95-98% reduction of S. aureus achieved for all duty cycles. The pulsing frequency was varied in intervals from 100 Hz - 10 kHz and appeared to have little effect on antimicrobial efficacy. However, when comparing pulsed with continuous exposure, an improvement in inactivation per unit optical energy was achieved, with results showing an increase of approximately 83% in optical efficiency.
Conclusions: These results suggest that under pulsed conditions a lower energy consumption and lower perceived brightness could be achieved, thus potentially providing improved operating conditions for medical/infection-control applications without compromising antimicrobial efficacy.