The aim of the experiment was the investigate whether bright lights at night and darkness during the day could prevent the sleep-wake cycle being disrupted during night-shifts.
Czeisler et al (1990) Aim
Method and Procedure8 men who were not used to the shift were assigned shifts beginning at 23.45 for 6 nightsThey were asked to do office workThey were restricted from caffeine and alcohol (checked through urine analysis)One group worked in regular light (150 lux) while another worked in bright light (7000 lux)Then instructed to go home and sleep in total darkness from 9-5pmCore body temperature was recorded continuously for both groupsGiven cognitive tests and self-report mood and alertness questionnaires
150 lux group
ResultsThe workers exposed to normal light (150 lux) had their mean temperatures drop during the night (which occurs during sleep)The group exposed to bright light (7000 lux) successfully adapted their circadian rhythm as their temperature dropped at midday. They also had improved results on all tests after 2-3 days (i.e. improved mood, alertness, concentration, overall cognitive ability).