What is the evidence for light therapy, specifically the newer "blue light" 470 nm therapy, for seasonal affective disorder (SAD)?
Laura Davies, MD
Professor of Psychiatry, University of Pittsburgh Medical Center; Chief, Division of Adult Academic Psychiatry, Western Psychiatric Institute and Clinic, Pittsburgh, Pennsylvania
Standardized and relatively attractive desktop-sized light units are readily available through Internet vendors; prices range from $200 to $400. These units typically deliver 10,000 lux of brightness with full-spectrum light. A typical course of therapy involves 30 to 60 minutes of light exposure each morning throughout the period of risk (ie, September through April). The major drawback of light therapy is the time involved: many patients lack the organization and motivation to persist with such a long course of therapy.
As a result, investigators are studying alternatives that may affect the circadian systems that mediate response to bright full-spectrum light. Two promising options are dawn simulation and negative air ionization at high flow rate, which can be administered during the final hours of sleep. Narrow-spectrum blue light (468-nm light at 607 microW/cm2, with a 27-nm half-peak bandwidth), administered via a light-emitting diode (LED), has been shown to suppress melatonin as does full-spectrum bright light. In one recent trial, narrow-spectrum blue light was shown to exert significant antidepressant effects.  However, as this form of light therapy also appears to require 45 minutes of daily morning administration, it is not clear whether it will offer any advantages over conventional light therapy.