"Lewy and colleagues have shown that human melatonin secretion can be suppressed by bright artificial light but not by light of regular indoor intensity. This finding stimulated attempts to modify winter depressive symptoms with bright artificial light. After this proved successful in a single patient, studies in four separate groups of patients at the NIMH (National Institutes on Mental Health) showed that extending the day with five to six hours of bright full-spectrum light had significant antidepressant effects whereas dimmer, control light treatments did not."