An evaluation of scheduled bright light and darkness on rotating shiftworkers: trial and limitations

The effectiveness of a program of scheduled bright light and dark to alter the circadian pacemakers of rotating shiftworkers were evaluated. Thirteen industrial workers were exposed to scheduled bright light of 6,000-12,000 lux on at least half of their 12-hr night shifts for 3 months, as well as ambient light of 1,200-1,500 lux. All 10 workers evaluated with urinary melatonin levels had morning melatonin suppression on the night shift, and 50% had a statistically significant circadian change. Although a few significant changes were noted concerning reported sleep and alertness, most findings concerning self-perceived alertness and performance at work, and sleep patterns were mixed and inconsistent. The major complaint was increased difficulty adjusting to being off work after the night shift during the light phase. The alteration in urinary melatonin levels is the first objective demonstration that the bright light technology can alter the circadian pacemakers of workers in an industrial setting. At this worksite, a number of interventions to lessen the effects of rotating shiftwork are being evaluated. Criteria are proposed that should be considered in evaluating a worksite for the use of bright light technology.