Bright light and LEET effects on circadian rhythms, sleep and cognitive performance

Shift work and jet lag can disrupt circadian rhythms, with detrimental effects on alertness, performance and sleep. This study examined the effects of two interventions to adapt circadian rhythms, sleep and performance to a 10-h phase delay of the work-rest cycle. Bright light was administered from 2200 to 0200 each night to promote phase delay of circadian rhythms. Low energy emission therapy (LEFT) was administered for 20 min prior to daytime sleep periods to promote sleep. Twelve subjects received bright light, 12 subjects received LEFT, 11 received both interventions and 10 control subjects received only placebo treatments. Bright light accelerated phase delay of the circadian melatonin rhythm after the work-rest schedule shift. Further, subjects who received bright light had greater total sleep time (TST) and improved sleep continuity. LEFT treatment produced a trend (p = 0.16) for increased TST, but LEET did not affect the melatonin circadian rhythm. After the schedule shift, cognitive performance measures showed few significant differences. Some minor improvements in cognitive performance were produced by light treatments but not by LEET. (C) 1997 John Wiley & Sons, Ltd.