Abstract
Light treatment stands as the first active clinical intervention for major depression, with an underpinning in basic lab research on the circadian timing system and seasonal physiological changes in animals. By contrast, pharmaceutical treatments were discovered as side effects of drugs targeted at other medical disorders. The first randomized, controlled clinical trial showed that winter depression (seasonal affective disorder) could remit by truncating long winter nights with bright artificial light in late evening and early morning. Morning light proved most effective, which implicated a change in circadian timing. Seasonality, however, is not essential for the light effect: The much larger cohort of patients with non-seasonal depression also responds to morning light. Bipolar depression can remit as quickly as after a single night awake, but with high risk of relapse after sleep the next night. By adding daily morning light treatment after the night awake, the remission is sustained. Circadian rhythm sleep disorders, especially with sleep onset insomnia, can be normalized by timed light treatment, avoiding recourse to hypnotic drugs. New applications of light treatment with promising initial data include attention deficit hyperactivity disorder, fibromyalgia and other pain disorders, and symptoms of Parkinson's disease and dementia.