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J Pineal Res. 2019 Jan 29:e12562. doi: 10.1111/jpi.12562. [Epub ahead of print]

Melatonin suppression is exquisitely sensitive to light and primarily driven by melanopsin in humans.

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Lyon Neuroscience Research Center, Integrative Physiology of the Brain Arousal Systems, Waking team, Inserm UMRS 1028, CNRS UMR 5292, Université Claude Bernard Lyon 1, Université de Lyon, F-69000, Lyon, France.
Department of Visual Neuroscience, Singapore Eye Research Institute, Singapore.
The Ophthalmology & Visual Sciences ACP, Duke-NUS Medical School, Singapore.



Light elicits a range of non-visual responses in humans. Driven predominantly by intrinsically photosensitive retinal ganglion cells (ipRGCs), but also by rods and/or cones, these responses include melatonin suppression. A sigmoidal relationship has been established between melatonin suppression and light intensity, however photoreceptoral involvement remains unclear.


In this study, we first modelled the relationships between alpha-opic illuminances and melatonin suppression using an extensive dataset by Brainard and colleagues. Our results show that 1) melatonin suppression is better predicted by melanopic illuminance compared to other alpha-opic illuminances, 2) melatonin suppression is predicted to occur at levels as low as ~1.5 melanopic lux (melanopsin-weighted irradiance 0.2 μW/cm²), 3) saturation occurs at 305 melanopic lux (melanopsin-weighted irradiance 36.6 μW/cm²). We then tested this melanopsin-weighted illuminance response model derived from Brainard and colleagues' data and show that it predicts equally well melatonin suppression data from our laboratory, although obtained using different intensities and exposure duration.


Together, our findings suggest that melatonin suppression by monochromatic lights is predominantly driven by melanopsin, and that it can be initiated at extremely low melanopic lux levels in experimental conditions. This emphasizes the concern of the non-visual impacts of low light intensities in lighting design and light-emitting devices. This article is protected by copyright. All rights reserved.


circadian; dose-response relationship; humans; light; mathematical model; melanopsin; melatonin


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