Night workers often experience high levels of sleepiness because of misalignment of the sleep/wake cycle from the circadian pacemaker, in addition to acute and chronic sleep loss.
Exposure to light, in particular short-wavelength light, can improve alertness and neurobehavioral performance. This randomized controlled trial examined the efficacy of blue-enriched polychromatic light to improve alertness and neurobehavioral performance in night workers.
Participants were 71 night shift workers (42 males; 32.8 ±10.5 years) who worked at least 6 hours between 2200 and 0800. Sleep/wake logs and wrist actigraphy were collected for 1–3 weeks, followed by 48-hour urine collection to measure the circadian 6-sulphatoxymelatonin (aMT6s) rhythm. On the night following at least two consecutive night shifts, workers attended a simulated night shift in the laboratory, which included subjective and objective assessments of sleepiness and performance. Workers were randomly assigned for exposure to one of two treatment conditions from 2300 to 0700 hours: blue-enriched white light (17 000 K, 89 lux; n = 36) or standard white light (4000 K, 84 lux; n = 35).
Subjective and objective sleepiness increased during the night shift in both light conditions, but no significant effects of light condition were observed. The 17 000 K light, however, did improve subjective sleepiness relative to the 4000 K condition when light exposure coincided with the time of the aMT6s peak.
This study suggests that, while blue-enriched light has potential to improve subjective sleepiness in night shift workers, further research is needed in the selection of light properties to maximize the benefits.
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