SCIENCE / MEDICINE : Light, Dark Reset Internal Clocks

Carefully timed doses of bright light and total darkness can help night shift workers quickly reset their internal clocks so they stay alert on the job and sleep soundly during the day, scientists reported last week in the New England Journal of Medicine. The approach appears to be the first quick, practical cure for the night shift blues, the on-the-job sleepiness and daytime insomnia that plague many of the nation’s 7 million night workers.

According to the principal developer, Dr. Charles A. Czeisler of Boston’s Brigham and Women’s Hospital, the technique works this way: People moving to the night shift reported to work--in this case, a hospital lab--at midnight and spent the next eight hours sitting at a desk. While they worked, a bank of lights 4 feet away shone with 16 cool-white 40-watt bulbs.

Then they drove home, pulled down blackout shades in their bedrooms and stayed in total darkness from 9 a.m. to 5 p.m. After just two days, the time on their internal clocks shifted almost 10 hours. So instead of hitting the low point in their daily cycle about 5 a.m., this happened around 3 p.m. when they were still asleep. Those who got the light-dark treatment noticed an immediate improvement in their alertness and performance and were able to sleep two hours longer a day.