Short-wavelength enrichment of polychromatic light enhances human melatonin suppression potency

The basic goal of this research is to determine the best combination of light wavelengths for use as a lighting countermeasure for circadian and sleep disruption during space exploration, as well as for individuals living on Earth. Action spectra employing monochromatic light and selected monochromatic wavelength comparisons have shown that short-wavelength visible light in the blue-appearing portion of the spectrum is most potent for neuroendocrine, circadian, and neurobehavioral regulation. The studies presented here tested the hypothesis that broad spectrum, polychromatic fluorescent light enriched in the short-wavelength portion of the visible spectrum is more potent for pineal melatonin suppression in healthy men and women. A total of 24 subjects were tested across three separate experiments. Each experiment used a within-subjects study design that tested eight volunteers to establish the full-range fluence-response relationship between corneal light irradiance and nocturnal plasma melatonin suppression. Each experiment tested one of the three types of fluorescent lamps that differed in their relative emission of light in the short-wavelength end of the visible spectrum between 400 and 500 nm. A hazard analysis, based on national and international eye safety criteria, determined that all light exposures used in this study were safe. Each fluence-response curve demonstrated that increasing corneal irradiances of light evoked progressively increasing suppression of nocturnal melatonin. Comparison of these fluence-response curves supports the hypothesis that polychromatic fluorescent light is more potent for melatonin regulation when enriched in the short-wavelength spectrum.