Assessment of Nitric Oxide Release In Vitro via Low-Level Daylight-Equivalent Blue or Red Light Irradiation

Conflicting evidence exists on whether blue or red light modulates nitric oxide (NO) release within skin cells. Using environmentally relevant doses, irradiances and spectral distribution akin to low-level sunlight, we provide evidence that broad-spectrum blue or red (including infrared) light fails to significantly increase NO release in skin cell monolayers compared to unexposed controls for each individual timepoint assessed. We discuss observed discrepancies between our work and recent photobiomodulation (PBM)-based studies presenting measurable upregulation, noting that significant NO induction typically requires high-powered light-emitting diodes (LEDs) or lasers used in clinical settings within a specific narrow spectral band. Thus, while our findings show no significant effect, they provide an important counterpoint for public health discussions on visible light exposure at terrestrial levels, particularly low-level exposures, between 15 and 30 min midday UK visible light exposure.