AimTo find out whether disturbances in the sleep-wake cycle created by working at night could be prevented by a treatment program of exposure to bright light during the night, and darkness during the day.
Method and procedure8 young men (aged 22-29) who were not used to shift work were asked to arrive at 23:45 for 6 nights of sedentary, office-based shift-work. They were asked not to drink caffeine or alcohol and this was checked by urine analysis.
One of the participants worked in ordinary indoor light (150 lux).
The other group were exposed to extreme bright light (7000 lux - equivalent to early morning light) during this nightshift and then instructed to go home and sleep in complete darkness from 9-5pm.
The core body temperature of participants (which falls during sleep) was recorded over the course of the research for both groups. They were given cognitive tests and self-report mood and alertness questionnaires.
ResultsMean temperatures of the group with ordinary light fell during the night, whereas after 4 days the temperature of the group exposed to bright light fell at midday.
The 'bright light' group had successfully adapted their circadian rhythms to the night-time work schedule, whereas the 'ordinary light' group had not (they continued experiencing the sleep pattern of the circadian rhythm at night when working)
The group exposed to the bright light showed improved results on all tests after 2-3 days, including improved mood, alertness, concentration, overall cognitive ability as well as shift in urinary excretion rate.
ConclusionDisturbances in the sleep-wake cycle, including associated declines in alertness, performance and quality of sleep, can be treated effectively with scheduled exposure to bright light at night and darkness during the day.