A new methodology to measure total fluence during pulsed light treatment based on a conversion efficiency factor

This work presents an indirect approach for estimating the radiant exposure (H_e = Q_light/A), or fluence, during pulsed light (PL) treatment by observing the rate of melting of ice in a petridish and temperature increase in a metal tray kept inside the PL chamber. It was proposed that any change (physical/chemical/microbiological) produced due to PL treatment is a function of H_e and thus can be correlated to H_e using Pratap-Singh-Ramaswamy (PSR) conversion efficiency factor. This hypothesis was tested for two treatments that involved heat exchanges during PL treatment: a) melting of ice (due to latent heat) and b) rise of sample temperature (due to sensible heat). Gathered data showed a strong correlation between the measured heat exchange parameters (thermal energy received Q_h, ice melted m_ice, temperature rise T_rise) and the incident radiant flux (H_e) at a particular location, thus validating the hypothesis. The PSR factor for different processes were fitted using a first-order model, wherein PSR_thermal, PSR_latent and PSR_sensible were evaluated as the slope of Q_h, m_ice, T_rise v/s H_e curves, respectively, and corresponding system configuration terms (δ_h, δ_i and δ_T) were evaluated as intercepts. The value of PSR_thermal was almost 2–3 folds better for the ice melting latent heat method, suggesting it to be a better candidate for adopting this methodology. The proposed methodology gave a good fit between the calculated and actual H_e values. The concept was also validated using data for PL destruction kinetics for different microbes (E coli K12, G. stearothermophilus, C. sporogenes) were established as 0.3212, 0.2395 cm²/J and 0.0925 cm²/J. Overall, this study lays the foundation of a simple, rapid and cost-effective technique to estimate the absorbed pulsed light fluence.