Optical design applied to an effective inactivation of airborne pathogens

The inactivation or airborne pathogens inside closed spaces is a critical issue that raised overwhelmingly during the current SARS-CoV 2 pandemic. Among the different technologies to achieve air sanification, the ultraviolet germicidal irradiation is a trending technique, also due to the fast development of more and more effective ultraviolet LED sources, that are expected to replace the mercury vapor lamps in the next few years. The positioning of LEDs inside cavities with highly reflective surfaces permits an enhancement of the internal irradiance and the development of compact devices. Optical simulations, by means of ray tracing, are fundamental, since an accurate irradiance estimation in presence of multiple internal reflections, scattering, light leaks outside the cavity and the sources angular emission distribution is not possible with only analytical calculations. Ray tracing permits to model the spatial irradiance inside the cavity by varying the components parameters to maximize the inactivation rate as a function of the air flow field. We discuss, on the basis of the experience on several related projects, the advantages of using the numerical approach to simulate these devices, focusing the attention onto the critical parameters which must be controlled to retrieve a reliable estimation of the system performance.