The Effects of Bright Light Exposure on ICU Nurses

In the majority of intensive care units, nurses work 12 hour shifts that consist of days and nights. Shift work outside of 6am-6pm has been reported to cause fatigue, induce sleep disorders, and cause metabolic disturbances. This shift to a nocturnal 'day' rather than diurnal, can result in reduced work performance, processing errors, accidents at work, absenteeism, and reduced quality of life. More chronically, those working at night have been shown to experience higher risks of heart disease, cancer and shorter median durations of life span. Much of this elevated risk is thought to be due to altered exposure to light, the dominant environmental cue regulating our circadian rhythms. As diurnal organisms much of our biology is regulated by the solar day. Acutely, bright light exposure (i.e., sun) regulates the phase of the biological clock principally through the suppression of melatonin, which biologically mediates increased alertness and in essence, 'our daytime alertness'. During the night melatonin gradually increases and induces tiredness and ultimately sleep. This, in part, is biology behind the use of melatonin in those with sleep disturbances or to mitigate jet lag, with cross-continental or transoceanic flights. In this study, the investigators will randomize nurses in the hospital to receive either high intensity white light (3,000 lux) or standard ambient white fluorescent (\~400 lx) light for 10 hours during their night shift. This high illuminance light, rich in blue spectrum, is what diurnal creatures, like humans, are exposed to during the day. The lights may subsequently be equipped with blue filters (442 nm) to heighten the exposure to the rich blue spectrum light. Exposure will commence at the beginning of the night shift (\~7pm) and continue for 10 hours. The rationale for terminating exposure prior to shift end is to foster an onset of sleep biology. At the end of each shift, the nurses will complete the Stanford Sleepiness Scale and the Psycho