CME: Light Therapy: Why, What, for Whom, How, and When (And a Postscript about Darkness).

Light therapy has become established as an evidence-based treatment for Seasonal Affective Disorder. Light impacts the timing and stability of circadian rhythms as expressed in sleep, mood, alertness, and cognition. Forty years of clinical trials and open treatment have led to guidelines for patient selection, using light alone or in combination with antidepressants (or lithium for bipolar depression). Mood and sleep disturbances can also respond to adjunct light therapy in a broader set of psychiatric, neurologic and medical illnesses. We specify criteria for choice of treatment devices: optimum dose (10,000 lux), spectrum (white light), exposure duration (30-60 minutes) and timing (early morning). Protocol adjustment requires continual monitoring with attention to rate of improvement and management of potential side effects.