The development and progression of winter depression and the effect of light therapy was assessed in 31 of 83 subjects who reached a Beck Depression Inventory (BDI) score of 15 (indicating severe depression) and were consequently given light therapy. The subjects were regularly evaluated with the BDI at 2-week intervals during the months before and after light therapy. The BDI score increased rapidly during the 4 weeks before treatment and fell immediately after treatment. A marked decrease in depression score was also seen with the Hamilton Depression Rating Scale (HDRS) and HDRS/SAD extension rating scale. Although light therapy had a beneficial effect in most of our subjects, it had little or no beneficial effect in a subgroup of non-responders, possibly because of a difference in the nature of the depression suffered.
