The effect of Bright light on Fatigue and sleepiness in night shift work nurses

In this study we assessed the effect of bright light emitted by light box on fatigue, and sleepiness in nurses. 44 healthy female shift work nurses were allocated into two groups of intervention and control. In the first stage, bright light was emitted to the nurses in the intervention group by the light box, and bright light was not emitted to the control group. In the next stage (one month later), we emitted bright light to the control group of first stage and vice versa (cross over). Main outcome measure, we assessed after intervention were fatigue and sleepiness. We measured fatigue (Visual Analogue Scale) and, sleepiness (Karolinska Scale), every hour, during next 24 hours. Almost all the time during 24 hours of the assessment of Visual Analogue Scale the trend of changes in two groups were in opposite direction. The mean value of two groups were statistically different.  In addition, about Karolinska Sleepiness Scale, the effect of intervention on the mean values of KSS during 24 hours was significant and the mean values in two groups were significantly different and the trend of changes in two groups were in opposite direction. The bright light exposure in nurses resulted in changing the trend of fatigue in opposite direction compared to the controls. The minimum of fatigue occurred at 4 am which was time of maximum fatigue in controls. Also, the trend of changes of KSS was in opposite direction in cases and minimum sleepiness was at 4 am.