BACKGROUND: Bright visible-spectrum light therapy has proven effective in the treatment of seasonal affective disorder (SAD) and recent basic research suggests that blue wavelengths approximately 470 nm account for that effectiveness. To more stringently test the importance of these wavelengths, bright red-light was used for the placebo (control) condition.
METHODS: Thirty subjects meeting DSM-IV criteria for SAD were randomized to narrow-band light-emitting diode panels emitting blue- or red-light in this 3-week, parallel, double-blind trial. Twenty-five subjects participated in an open-label blue-light follow-up. Subjects were divided in a blinded, post hoc manner into two groups: SAD only and those experiencing depression with seasonal intensification. The outcome was assessed using Hamilton Depression Rating Scale-17 item version (HAMD-17) and the Structured Interview Guide for the Hamilton Depression Rating Scale-SAD version. Responders were defined by Clinical Global Impression-Improvement scale.
RESULTS: HAMD-17 scores improved more under the blue-light condition (51%) than under the red-light condition (32%) (P=.05). Further, in the blue arm 60% of subjects responded compared with 13% in the red arm (P=.01). During the open-label phase, subjects from both double-blind arms improved over baseline. SAD alone patients responded numerically better to treatment than those experiencing depression with seasonal intensification during both treatment periods.
CONCLUSIONS: Narrow bandwidth blue-light therapy proved superior to red-light therapy. Blue-light therapy produced results similar to both previous 10,000 lux visible-spectrum light studies and many medication studies. The use of bright red panels supported claims that wavelengths of approximately 470 nm account for the documented effectiveness of light therapy.
