DARK GOGGLES AND BRIGHT LIGHT IMPROVE CIRCADIAN-RHYTHM ADAPTATION TO NIGHT-SHIFT WORK

We compared the contributions of bright light during the night shift a nd dark goggles during daylight for phase shifting the circadian rhyth m of temperature to realign with a 12-hour shift of sleep. After 10 ba seline days there were 8 night-work/day-sleep days. Temperature was co ntinuously recorded from 50 subjects. There were four groups in a 2 x 2 design: light (bright, dim), goggles (yes, no). Subjects were expose d to bright light (about 5,000 lux) for 6 hours on the first 2 night s hifts. Dim light was <500 lux. Both bright light and goggles were sign ificant factors for producing circadian rhythm phase shifts. The combi nation of bright light plus goggles was the most effective, whereas th e combination of dim light and no goggles was the least effective. The temperature rhythm either phase advanced or phase delayed when it ali gned with daytime sleep. However, when subjects did not have goggles o nly phase advances occurred. Goggles were necessary for producing phas e delays. The most likely explanation is that daylight during the trav el-home window after a night shift inhibits phase-delay shifts, and go ggles can prevent this inhibition. Larger temperature-rhythm phase shi fts were associated with better subjective daytime sleep, less subject ive fatigue and better mood.