Attention deficit hyperactivity disorder BLT Bright light therapy CCT Correlated colour temperature CIE Commission Internationale de l'Eclairage CRSWD Circadian rhythm sleep-wake disorders DLMO Dim-light melatonin onset EEG Electroencephalogram GHT Geniculohypothalamic tract IGL Intergeniculate leaflet ipRGC Intrinsically photosensitive retinal ganglion cell LED Light-emitting diode PRC Phase response curve RGC Retinal ganglion cell RHT Retinohypothalamic tract RN Raphe nuclei SAD Seasonal affective disorder SCN Suprachiasmatic nuclei SSRI Selective serotonin reuptake inhibitor SWA Slow wave activity UV Ultraviolet Somnologie 3 • 2019 147

In the human, cone photoreceptors (L, M, and S) and the melanopsincontaining, intrinsically photosensitive retinal ganglion cells (ipRGCs) are active at daytime light intensities. Signals from cones are combined both additively and in opposition to create the perception of overall light and color. Similar mechanisms seem to be at work in the control of the pupil's response to light. Uncharacterized however, is the relative contribution of melanopsin and S cones, with their overlapping, short-wavelength spectral sensitivities. We measured the response of the human pupil to the separate stimulation of the cones and melanopsin at a range of temporal frequencies under photopic conditions. The S-cone and melanopsin photoreceptor channels were found to be low-pass, in contrast to a band-pass response of the pupil to L-and M-cone signals. An examination of the phase relationships of the evoked responses revealed that melanopsin signals add with signals from L and M cones but are opposed by signals from S cones in control of the pupil. The opposition of the S cones is revealed in a seemingly paradoxical dilation of the pupil to greater S-cone photon capture. This surprising result is explained by the neurophysiological properties of ipRGCs found in animal studies. Distinct neural pathways process signals originating in cone photoreceptors for visual perception. Luminance pathways combine signals from separate classes of cones synergistically, providing a spectrally broadband indication of the overall light intensity at each location in the retinal image. Red-green and blue-yellow chromatic channels combine signals from separate classes of cones in an opponent (subtractive) fashion, providing sensitivity to the relative spectral content of light and supporting the perception of color independent of luminance (1).A parallel set of pathways contributes to the response of the pupil of the eye to light. Most familiar is a synergistic cone effect that causes the pupil to constrict in response to increased luminance. Illustrating a commonality of principles that characterize neural mechanisms for perception and pupil response, rectified signals from red-green and blue-yellow opponent channels also contribute to the pupil's light response (2-7).Recently, it has been discovered that mammalian retinas contain an additional photoreceptor class that also operates under daylight conditions. Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin, which has a peak spectral sensitivity (480 nm) between that of S and M cones (8, 9). Among other, "non-image-forming" functions of the eye, melanopsin-containing ipRGCs contribute to a delayed and sustained constriction of the pupil (10). Studies in patients with loss of photoreceptor function (11) suggest that melanopsin may also contribute to conscious visual perception.The discovery of an additional photoreceptor class raises the fundamental question of how melanopsin signals are combined with those from the cones. Do melanopsin signals add to con...

Ocular light exposure has important influences on human health and well-being through modulation of circadian rhythms and sleep, as well as neuroendocrine and cognitive functions. Prevailing patterns of light exposure do not optimally engage these actions for many individuals, but advances in our understanding of the underpinning mechanisms and emerging lighting technologies now present opportunities to adjust lighting to promote optimal physical and mental health and performance. A newly developed, international standard provides a SI-compliant way of quantifying the influence of light on the intrinsically photosensitive, melanopsin-expressing, retinal neurons that mediate these effects. The present report provides recommendations for lighting, based on an expert scientific consensus and expressed in an easily measured quantity (melanopic equivalent daylight illuminance (melaponic EDI)) defined within this standard. The recommendations are supported by detailed analysis of the sensitivity of human circadian, neuroendocrine, and alerting responses to ocular light and provide a straightforward framework to inform lighting design and practice.