Seasonal affective disorder is not yet accepted as a distinct psychological disorder. Rather, other mood disorders (major depression, bipolar depression, dysthymia) can be qualified with a "seasonal pattern specifier." What this means, is that the primary mood disorder appears to vary according to the seasons of the year. Whether this represents a distinct psychological disorder, or simply that seasonal variations in weather and sunlight can trigger a depressive or manic episode, remains to be clarified. However, our studies show that numerous sessions in our machine serve to improve the symptoms of depression in a large percentage of people with all types of mood disorders.