Effects of Distance, Temperature, and Relative Humidity on the Irradiance of Ultraviolet‐C Germicidal Lamp: A Quantitative Study.

Ultraviolet germicidal irradiation (UVGI) as an engineering control against pathogenic microbes necessitates a clear understanding of operational parameters and environmental effects on inactivation rates. Here, we investigated the variation laws of ultraviolet‐C (UV‐C) irradiance under the influence of distance, ambient conditions of temperature, and relative humidity (RH) in a dark chamber using 30‐W low‐pressure mercury lamps, and all data were analyzed with curve fitting methods. UV‐C irradiances in each plane were measured as the distance adjusting between 0.5 and 1.2 m, and a threshold of 70 μW/cm2 was utilized to calculate the effective irradiation area. For the temperature and RH, UV‐C irradiances were measured at 1 m perpendicular from the lamp axis at the lamp midpoint, with the ambient temperature increasing from 15.5°C to 40°C and RH adjusting from 10% to 97%. Results showed that the UV‐C irradiance and effective irradiation area exhibited a notable decrease as the distance increased, both corresponded to polynomial 2nd order fits. The UV‐C lamps operate at maximum efficiency at 20°C. Temperature above or below the optimum value will decrease UV output, especially when the ambient temperature exceeds 38°C and the irradiance decreases by 16% compared to the observed maximum. However, the impact of RH on radiant power is negligible with the UV‐C irradiance maintaining an overall steady state (84–91 μW/cm2) in the 10%–97% RH range. The use of the measurement and modeling techniques demonstrated in this study may help understand various ambient conditions that influence the irradiance of UV‐C and improve reliability and working performance of UVGI systems through better design. [ABSTRACT FROM AUTHOR]