Exposure to ambient light in patients with winter seasonal affective disorder.

In a study of the quantitative relationship between ambient light and depression in winter seasonal affective disorder, 13 outpatients and 13 normal comparison subjects each wore a light monitor for 1 week. The patients and normal subjects showed similar light exposure profiles; among the patients, severity of depression was inversely related to photoperiod, and there was a trend toward a correlation between greater severity of depression and later time of onset of morning light exposure. These findings suggest that vulnerability to short photoperiods may be related to depression in winter seasonal affective disorder.