We have previously shown that exposure of the eyes to bright light, but not ordinary room light, can reverse the winter depressive symptoms in patients with seasonal affective disorder (SAD). This light treatment may be effective during the morning, the evening or even during ordinary daylight hours. Normal subjects with no history of winter difficulties do not seem to benefit from this light treatment. This past year we have gone on to study whether light in a narrow band of the visual spectrum (blue or red) is as effective as the full-spectrum light used previously. We have also asked whether normal subjects who complain of mild winter difficulties might benefit from conventional bright light treatment. In a crossover study on 21 subjects we found that although full- spectrum light tended to be more effective than either blue or red light, this did not reach statistical significance, perhaps because the narrow-band light was clinically active to some degree. If this is so, it would suggest that the antidepressant effects of light in SAD are mediated by wavelengths that span the full visual spectrum. A separate study of full-spectrum light in 40 normal subjects, 20 with and 20 without a history of mild winter difficulties, such as low energy level or decreased productivity, showed that the former group benefited from light treatment whereas the latter group did not. The degree of improvement was related to the duration of treatment, 5 hours per day proving superior to 2 hours per day. Since there seems to be a high prevalence of normal subjects with mild winter difficulties, this finding may have widespread public health implications.
