LAUSR

Mobile whole‐room UVGI devices are used in healthcare settings to control surface‐borne pathogens. Unfortunately, no standard method comparing the efficacy of these devices is available. We accessed the effect of shadows on UVC 254 nm inactivation. The evaluation of a mobile whole‐room UVGI device used spores of Bacillus atrophaeus as a surrogate for Clostridium difficile and Staphylococcus aureus as a surrogate for MSRA. Inactivation after 10 min of exposure varied significantly depending on whether the spores received direct UV exposure (4.3 log reduction), both direct and reflected UV exposure (3.0–4.0 log reduction) or reflected UV exposure alone (<1.0 log reduction). The susceptibility (z‐value) for inactivation of B. atrophaeus spores on a glass surface was estimated to be 0.00312 m2 J−1. Staphylococcus aureus microbial log reductions were approximately 5.5 for direct UV exposure, 3.6–5.2 for both direct and reflected UV exposure and approximately 2.75 for only reflected UV exposure. Our measurement of reflected dose ranged from 0.46% to 1.47%. Based on our findings, B. atrophaeus spores should be considered as a model organism for testing the impact of shadows on mobile whole‐room UVGI device inactivation. Optimizing the reflected component of whole‐room UVGI is important, especially for UVC‐resistant organisms.