Light levels in a modern intensive care unit: Impact of time of year, window directionality, and outdoor light levels

The intensive care unit (ICU) environment is designed for the care of acutely ill patients, with lighting conditions reflecting the needs of the busy clinical setting. Earlier ICU studies suggested that daytime and nighttime light levels were misaligned with those required for circadian rhythm entrainment, which can impact patient sleep-wake cycles and recovery from critical illness. In this investigation in San Diego, California, a coastal US city with over 260 days of sunshine annually, we performed a detailed evaluation of light levels in a contemporary academic medical-surgical ICU constructed in 2016, which features modern lighting and floor-to-ceiling windows in each of the 24 rooms. Using light meters mounted on poles and located directly behind the head of each patient's bed, our analysis of nearly 90,000 hours of data revealed daytime ICU light levels consistently lower than 150 lx, similar to studies in older ICUs and many magnitudes lower than outdoor levels at identical times. Hence, despite the modern design, we found that little to no light from the ~100 ft2 windows reached the patient. While daytime light levels were low across all ICU rooms, those with windows facing South and Northwest featured higher light levels than those facing Southeast and Northeast, suggesting a contribution of window direction to ICU light levels.