Lux vs. wavelength in light treatment of Seasonal Affective Disorder

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Abstract
Objective: Published dosing guidelines for treatment of Seasonal Affective Disorder (SAD) refer to photopic lux, which is not appropriate for short‐wavelength light. Short wavelengths are most potent for many non‐visual responses to light. If SAD therapy were similarly mediated, standards utilizing lux risk overestimating necessary dose. We investigated antidepressant responses to light using two light‐emitting diode (LED) sources, each emitting substantial short‐wavelength light, but ®) or blue‐enriched white‐appearing light in 18 moderately‐depressed adults (12F, 49.1 ± 9.5 years). Equivalent numbers of photons within the short‐wavelength range were emitted, but the white source emitted twice as many photons overall and seven‐fold more lux. Results: Depression ratings (SIGH‐ADS; http://www.cet.org) decrease averaged 82% (SD = 17%) from baseline (P < 0.0001) in both white‐ and blue‐light groups. Both sources were well tolerated. Conclusion: Short‐wavelength LED light sources may be effective in SAD treatment at fewer lux than traditional fluorescent sources.