Multispectral Antimicrobial Blue Light (aBL) Systems for Continuous Decontamination of Food-Contact Surfaces and Environmental Matrices

Antimicrobial blue light (aBL) within the visible violet–blue spectrum has emerged as a promising non-chemical strategy for microbial control, yet its performance across environmentally realistic matrices and surfaces remains insufficiently characterised. Here, we evaluate a continuous-exposure aBL LED system operating within the visible 407–421 nm range for its antimicrobial efficacy against Escherichia coli K-12 MG1655 and Bacillus cereus NCTC 11143 across liquid cultures, agar surfaces, and representative built-environment materials (glass and steel bar). Bacterial inactivation was quantified using culture-based enumeration and flow cytometric viability profiling. The system delivered a controlled irradiance of 0.72 mW/cm2 at 58 cm, corresponding to cumulative doses of 2.59–62.23 J cm−2 over 1–24 h of exposure. Significant, time-dependent reductions in viability were observed across all matrices relative to fluorescent-light controls, with near-complete or complete loss of recoverable cells on solid surfaces following prolonged exposure. Flow cytometric analyses revealed progressive transitions from viable to injured and dead cell populations, consistent with photodynamic inactivation mediated by endogenous photosensitiser activation and reactive oxygen species generation. These findings demonstrate that continuous visible-light aBL illumination can achieve effective multisurface microbial inactivation under moderate irradiance conditions compatible with occupied environments, supporting its translational potential as a sustainable, non-chemical decontamination strategy for healthcare, food-processing, and built environments.