Fig. 1.

Melatonin profiles from seven subjects who showed more melatonin suppression after the dim week than after the bright week (subjects C08, C09, C10, C13, C25, C26 and C28). Vertical lines indicate the period of 500-lux light exposure on the test nights. At all other times the light intensity was <15 lux. Profiles were averaged so that the 3 hr of light exposure were aligned. The clock times shown are for subjects who had the light exposure from 1:00 to 4:00. The others had the light from 0:30 to 3:30. Before group averaging, each profile was converted into percentages of its respective baseline post-value. The baseline post-value was the average melatonin level of the last four samples collected in the 3-hr interval during the baseline night, e.g. 2:30, 3:00, 3:30 and 4:00.