ABSTRACT
Night-time melatonin secretion was measured in five depressed inpatients with seasonal affective disorder before and after 1-week of morning and evening exposure to bright (3000 lux) and dim (300 lux) light. Analysis of variance by ranks showed no differences in timing of melatonin secretion but statistically significant differences in plasma melatonin levels. There was a decrease of the area under the curve after bright light and a very robust rebound after exposure to dim light. The failure to constitute a parallel group of patients in a crossover design did not permit to control for an ordering effect of light exposure. These findings raise many questions concerning the diurnal sensitivity to different intensities of light in seasonal affective disorder.
