"Blue in the Face. Editorial Sleep Medicine (2009); 10(3):277-278
Michael Terman.

"It has taken some time for data on the potential clinical benefits of short-wavelength exposure to appear. In a study of winter depression, bright narrow-band blue light was superior to dim red light. Although this result may indicate a benefit relative to placebo, it does not demonstrate the specific efficacy of blue light. Nevertheless, this study motivated the first mass-market initiative for light therapy apparatus, using blue light-emitting diodes, with distribution including the Costco chain. Many clinicians, naive to the issues, became enthusiasts. There was, however, concern in the ophthalmology community that such short-wavelength exposure could cause direct long-term damage to retinal structures, exacerbation of age-related macular degeneration, and a photosensitization hazard with common medications including certain psychotropic drugs. The ubiquitous yellowing of the lens with age, which largely blocks short-wavelength transmission, might indeed serve a protective function. Counteracting this lens filter with massive doses of blue light in the elderly might be counterproductive."

"By assiduous methodology that approximates the application of light therapy, the study allows us to put exaggerated, commercially inspired claims in perspective, and question whether blue light 'enrichment' represents a major conceptual, technological or clinical advance."

"The story actually long predates the discovery of melanopsin and its non-image-forming functions. The earliest light therapy studies (and commercial apparatus) used 'full-spectrum' fluorescent light - an ill-defined quantity that boosts short-wavelength exposure. The choice of lamp - which was inspired by industry consultants to the National Institute of Mental Health - was not based on physiological data, but rather on the face-relevant assumption that outdoor skylight contains a lot of blue-light and therefore should be good for you by comparison with indoor artificial light. ...the need for blue light augmentation was tested with lamps that attenuated short-wavelength emission. The antidepressant response remained robust. Nevertheless, the aggressive marketing of full-spectrum light therapy continues. For one thing, the profit margin is higher than for conventional fluorescent lamps."
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