Light exposure at night may disrupt the circadian timing system and is associated with various health disorders.
Previous definitions of circadian spectral sensitivity primarily focused on dark-adapted conditions with limited wavelength sensitivity.
This research suggests that light-adapted circadian spectral sensitivity may be predominantly blue, with a narrower range than previously thought.
Extended exposure to light-adapted conditions showed that the circadian spectral sensitivity includes a peak at 477 nm and a range of 438 to 493 nm.
The findings could aid in developing LED light sources that minimize circadian disruption in daily life.
Simplified
Electric light has enabled humans to conquer the night, but light exposure at night can disrupt the circadian timing system and is associated with a diverse range of health disorders. To provide adequate lighting for visual tasks without disrupting the human circadian timing system, a precise definition of circadian spectral sensitivity is required. Prior attempts to define the circadian spectral sensitivity curve have used short (≤90-min) monochromatic light exposures in dark-adapted human subjects or in vitro dark-adapted isolated retina or melanopsin. Several lines of evidence suggest that these dark-adapted circadian spectral sensitivity curves, in addition to 430- to 499-nm (blue) wavelength sensitivity, may include transient 400- to 429-nm (violet) and 500- to 560-nm (green) components mediated by cone- and rod-originated extrinsic inputs to intrinsically photosensitive retinal ganglion cells (ipRGCs), which decay over the first 2 h of extended light exposure. To test the hypothesis that the human circadian spectral sensitivity in light-adapted conditions may have a narrower, predominantly blue, sensitivity, we used 12-h continuous exposures of light-adapted healthy human subjects to 6 polychromatic white light-emitting diode (LED) light sources with diverse spectral power distributions at recommended workplace levels of illumination (540 lux) to determine their effect on the area under curve of the overnight (2000-0800 h) salivary melatonin. We derived a narrow steady-state human with a peak at 477 nm and a full-width half-maximum of 438 to 493 nm. This light-adapted Circadian Potency spectral sensitivity permits the development of spectrally engineered LED light sources to minimize circadian disruption and address the health risks of light exposure at night in our 24/7 society, by alternating between daytime circadian stimulatory white light spectra and nocturnal circadian protective white light spectra.
Key numbers
5×
Variation in Melatonin AUC
Comparison of melatonin AUC across different LED light sources.
477 nm
Peak Circadian Potency Wavelength
Identified peak of the .
55 nm
Full-Width Half-Maximum
Width of the .
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Conflict of Interest Statement: M.M.-E., A.H., and R.G. are inventors on patent application PCT/US2019/041728 assigned to Circadian ZircLight Inc., which discloses circadian optimized spectrally engineered light sources including day and night LEDs using the Circadian Potency function described in this article, and issued patents US9827440, CN105265025, EP2982224, JP6391669, CA2908659, KR101986700, AU2018241062. M.M.E. is the chairman and CEO and holds equity and receives compensation from Circadian ZircLight, Inc. and Circadian Technologies Inc. R.G. and A.H. are employees of Circadian Technologies, Inc.
