Lighting in intensive care units: A systematic review of patient outcomes and directions for future research

Objectives Patients admitted to ICUs are frequently exposed to disrupted light–dark cycles due to limited daylight exposure and inappropriate electrical lighting in terms of intensity, duration, timing, and spectral distribution. Such disruptions can impair circadian entrainment, thereby negatively affecting patient outcomes. Consequently, lighting interventions have been proposed to optimise the ICU environment and patient outcomes, but guidance for ICU lighting design remains limited. This review aimed to synthesise research from the past 10 years, examining the impact of lighting conditions and interventions on health outcomes in ICU patients. Methods The review was registered in PROSPERO and conducted in accordance with PRISMA guidelines. Six databases were searched for studies published between 2015 and 2026. Two independent reviewers applied inclusion and exclusion criteria, screened studies, and assessed methodological quality using established critical appraisal tools. Results A total of 12,674 studies were screened, and 28 studies met inclusion criteria. Of these, fourteen studies investigated lighting interventions and their effects on health outcomes, including dynamic lighting, static lighting, (bright) light therapy, and multicomponent lighting studies. The remaining studies investigated naturalistic lighting conditions through either comparisons of existing ICU lighting conditions or single observations. Studies showed high heterogeneity in findings, health outcomes assessed, and methodologies used to evaluate both lighting conditions and health outcomes. Conclusions Although some studies suggest potential benefits of specific lighting interventions, the limited evidence and inconsistent reporting of lighting conditions prevent definitive conclusions about their effects on health outcomes in ICU patients. Implications for clinical practice While current research does not yet provide clear guidance for ICU lighting design or the use of lighting interventions, the field is advancing. Prioritising consistent and transparent lighting assessment, alongside multidisciplinary collaboration and larger clinical trials, will help generate the data needed to inform future practice and support the development of meaningful ICU lighting standards.