Clinical and chronobiological effects of light therapy on nonseasonal affective disorders.

Light therapy (bright or dim light) was given at different times (morning or evening) to 27 unmedicated patients with nonseasonal depression (according to DSM-III-R criteria) and 16 normal volunteers. Circadian rhythms in body temperature were measured before and after light therapy. Bright light significantly improved clinical symptoms of depression, as measured by the Hamilton Rating Scale for Depression (HRSD), independent of the time of phototherapy. Dim light therapy had no effect on HRSD scores. Circadian rhythms of body temperatures in patients with affective disorder were more sensitive to the entraining effects of bright light than those of normal subjects, but these effects were not related to clinical improvement. Bright light exposure has an antidepressant effect on patients with nonseasonal depression, but the effect is unlikely to be mediated via the same circadian system that regulates body temperature.