CANDLE: The critical analysis of the nocturnal distribution of light exposure - A prospective pilot study quantifying the nocturnal light intensity on a critical care unit.

Patients with critical illness have disrupted circadian rhythms, which can lead to increased morbidity, mortality and length of intensive care unit stay. Light intensity within the intensive care unit influences the circadian rhythm and may therefore impact on patient outcome. We performed an observational single-centre pilot study monitoring nocturnal light exposure of intensive care unit patients between November and December 2016. As there are currently no medical guidance on recommended light levels, we audited our findings against building regulation standards. The median light intensity was 1.5 lux, which is below the 20 lux standards; however, there were significant outliers. There was positive correlation between patient illness severity based on SOFA score and maximum lux (R = 0.45, P = 0.026); however, there was no relationship between patient illness severity and median lux exposure (R = 0.23, P = 0.28). As illness severity increased so did the time spent greater than 20 lux (R = 0.59, P = 0.0021), and the individual occasions where lux breached the 20 lux limit (R = 0.52, P = 0.009). There was no relationship between illness severity of neighbouring patients and maximum lux (R = -0.11, P = 0.69) or neighbouring illness severity and median lux (R = -0.04, P = 0.87). This preliminary work will form the basis of future projects, including national guidance and evaluating the impact of environmental light on patient-centred outcomes.