Architectural and Operational Drivers of Bedside Light Exposure Across Neonatal, Paediatric, and Adult Intensive Care Units: A Multicentre Real-World Study

Light is a critical regulator of circadian physiology, yet its delivery in intensive care units (ICUs) is primarily determined by architectural features and clinical workflows rather than by biological timing. This multicentre study (34 ICUs across nine hospitals) investigated bedside light exposure (illuminance and correlated colour temperature [CCT]) in neonatal (NICU), pediatric (PICU), and adult ICUs under routine operational conditions. Measurements were performed at the patient’s eye level during morning, afternoon, and evening/night periods, with ceiling luminaires switched on and off, and stratified by window proximity. Extreme operational heterogeneity was observed, with median morning bedside illuminance spanning more than a tenfold range across centres, and most ICUs failing to reach either the biologically referenced daytime level of ≥200 lux or the EN 12464-1 bedside task reference level of 500 lux. Artificial lighting increased illuminance but did not consistently mitigate spatial inequities related to window proximity. Spectral characteristics varied markedly at the same time. The use of artificial lighting frequently altered CCT, often reducing it by more than 1500 K, thereby overriding natural daylight cues and shifting the spectral environment toward an earlier circadian phase. These findings highlight the need to treat ICU lighting as a designable, population-sensitive environmental exposure, integrating architectural layout, operational practice, and temporal intent to support both clinical care and circadian health.