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    Photons, clocks, and consciousness.
    J Biol Rhythms 2005 Aug;20(4):314-25
    Department of Neurology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
    Light profoundly impacts human consciousness through the stimulation of the visual system and powerfully regulates the human circadian system, which, in turn, has a broad regulatory impact on virtually all tissues in the body. For more than 25 years, the techniques of action spectroscopy have yielded insights into the wavelength sensitivity of circadian input in humans and other mammalian species. The seminal discovery of melanopsin, the photopigment in intrinsically photosensitive retinal ganglion cells, has provided a significant turning point for understanding human circadian phototransduction. Action spectra in humans show that the peak wavelength sensitivity for this newly discovered sensory system is within the blue portion of the spectrum. This is fundamentally different from the three-cone photopic visual system, as well as the individual rod and cone photoreceptor peaks. Studies on rodents, nonhuman primates, and humans indicate that despite having a different wavelength fingerprint, these classic visual photoreceptors still provide an element of input to the circadian system. These findings open the door to innovations in light therapy for circadian and affective disorders, as well as possible architectural light applications.

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    Photoreception for circadian, neuroendocrine, and neurobehavioral regulation.
    J Physiol Anthropol 2007 Mar;26(2):87-94
    Department of Neurology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
    In the art and science of lighting, four traditional objectives have been to provide light that: 1) is optimum for visual performance; 2) is visually comfortable; 3) permits aesthetic appreciation of the space; and 4) conserves energy. Over the past 25 years, it has been demonstrated that there are nonvisual, systemic effects of light in healthy humans. Furthermore, light has been used to successfully treat patients with selected affective and sleep disorders as well as healthy individuals who have circadian disruption due to shift work, transcontinental jet travel, or space flight. Read More
    Nonvisual ocular photoreception in the mammal.
    Methods Enzymol 2005 ;393:746-55
    Department of Ophthalmology and Visual Sciences, Washington University Medical School, St. Louis, Missouri 63110, USA.
    Rodents blind from outer retinal (rod and cone) degeneration still retain several light-dependent phenomena, including entrainment of the circadian clock and pupillary light responsiveness. This paradox is explained by the presence of intrinsically photosensitive retinal ganglion cells in the inner retina. These cells have unique properties, including a novel action spectrum, resistance to bleaching and adaptation under continuous light, and resistance to vitamin A depletion. Read More
    Sensitivity of the human circadian system to short-wavelength (420-nm) light.
    J Biol Rhythms 2008 Oct;23(5):379-86
    Department of Neurology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
    The circadian and neurobehavioral effects of light are primarily mediated by a retinal ganglion cell photoreceptor in the mammalian eye containing the photopigment melanopsin. Nine action spectrum studies using rodents, monkeys, and humans for these responses indicate peak sensitivities in the blue region of the visible spectrum ranging from 459 to 484 nm, with some disagreement in short-wavelength sensitivity of the spectrum. The aim of this work was to quantify the sensitivity of human volunteers to monochromatic 420-nm light for plasma melatonin suppression. Read More
    Regulation of mammalian circadian behavior by non-rod, non-cone, ocular photoreceptors.
    Science 1999 Apr;284(5413):502-4
    Department of Biology, Alexander Fleming Building, Imperial College of Science, Technology and Medicine, London, SW7 2AZ, UK.
    Circadian rhythms of mammals are entrained by light to follow the daily solar cycle (photoentrainment). To determine whether retinal rods and cones are required for this response, the effects of light on the regulation of circadian wheel-running behavior were examined in mice lacking these photoreceptors. Mice without cones (cl) or without both rods and cones (rdta/cl) showed unattenuated phase-shifting responses to light. Read More