Do Winter Depressives Experience Summer Nights in Winter?

The discovery of the antidepressive effects of light1 in seasonal affective disorder, winter type,2 has inspired explanations of pathogenesis of and therapy for this disorder in terms of circadian (dys)regulations. The original hypothesis of day length being the crucial variable was rapidly rejected.3 Subsequently, circadian phase4 and the daily total number of photons received by the patient3 were proposed as relevant factors. Unfortunately, neither of these proposals appeared to be compatible with all experimental data. In the present study, aspects of the previous hypotheses are put together into a new hypothesis, the outlines of which will be discussed.