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      Your body has a non-linear "dose-response" to light. This graph shows you how light of various intensities translate to a shift in your circadian timing.

      When you see light in the morning, it makes your day shorter, and when you see bright light at night, you stay up later.

      "Phase shift" shows how much you can move your body clock in just one night if you see it for long enough (a few hours) at the right time of day, typically before bed. Also, you can see how the light compares to being outdoors on a sunny day, which can shift your body's internal clock by up to 3 hours. This is how your body adjusts its clock when traveling to another timezone.

      To find this number, we're using a best fit from several published studies, with subjects who viewed light exposures ranging from 90 minutes to 6 hours.

      ...
      What's this?

      "EDI" is "equivalent daylight illuminance" and expresses how much melanopic stimulation a light has with a similar level of daylight (D65). Melanopic irradiance describes how the melanopsin-containing cells in your retina react to light. These cells provide the major input to the circadian pacemaker at high light levels. At lower levels, and when things are changing, the rods and cones appear to provide an important part of the response. For melanopic quantities, values below 5 equivalent daylight lux have little effect in shifting your circadian phase, and more than about 500 equivalent daylight lux is expected to saturate the melanopic response. [Lucas 2014, Gooley 2010]

      ...
      What's this?
      If you have a 'lux' or 'lumen' value, these numbers can give you an easy way to compare light sources. Two devices with the same visual brightness often have a different circadian impact.

      All the spectral data feeds are licensed for reuse under a
      Creative Commons Attribution 4.0 International License.

      Download spectral data for this page as a .CSV

      We spent some time and money getting all this data,
      so we thought other people should be able to use it.

      Everything else (code, analysis, images, etc.) is
      Copyright f.lux Software LLC 2011-2015.

      If you've read this far, you can also make a table...

      Data sources

      NOAA/NGDC Energy Spectra

      Selected references

      al Enezi, Jazi, et al. "A 'melanopic' spectral efficiency function predicts the sensitivity of melanopsin photoreceptors to polychromatic lights." Journal of biological rhythms 26.4 (2011): 314-323.
      Bierman, Andrew, Mariana G. Figueiro, and Mark S. Rea. "Measuring and predicting eyelid spectral transmittance." Journal of biomedical optics 16.6 (2011): 067011.
      Brainard, George C., et al. "Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor." The Journal of Neuroscience 21.16 (2001): 6405-6412.
      Brown, Timothy M., et al. The melanopic sensitivity function accounts for melanopsin-driven responses in mice under diverse lighting conditions. PloS one 8.1 (2013): e53583.
      Chang, Anne-Marie, et al. "Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness." Proceedings of the National Academy of Sciences 112.4 (2015): 1232-1237.
      CIE. (1926). Commission Internationale de l’Éclairage Proceedings, 1924. Cambridge: Cambridge University Press.
      CIE. (1932). Commission Internationale de l’Éclairage Proceedings, 1931. Cambridge: Cambridge University Press.
      CIE 170-1:2006. "Fundamental Chromaticity Diagram with Physiological Axes" Commission Internationale de l’Éclairage Proceedings, 2006.
      CIE TN 003:2015. Report on the First International Workshop on Circadian and Neurophysiological Photometry, 2013.
      Cleve, K. "The approach of the butterflies to artificial light sources." Mitt. Deut. Ent. Ges 23 (1964): 66-76.
      Gall, Dietrich, and Karin Bieske. "Definition and measurement of circadian radiometric quantities." Proceedings of the CIE Symposium ‘04 on Light and Health. 2004.
      Gooley, Joshua J., et al. "Exposure to room light before bedtime suppresses melatonin onset and shortens melatonin duration in humans." Clinical Endocrinology and Metabolism 96.3 (2010): E463-E472.
      Gooley, Joshua J., et al. "Spectral responses of the human circadian system depend on the irradiance and duration of exposure to light." Science Translational Medicine 2.31 (2010): 31ra33-31ra33.
      Govardovskii, Victor I., et al. "In search of the visual pigment template." Visual neuroscience 17.04 (2000): 509-528.
      International Commission on Non-Ionizing Radiation Protection. "ICNIRP Guidelines on limits of exposure to incoherent visible and infrared radiation." Health Physics 105.1 (2013): 74-96.
      International Electrotechnical Commission. "IEC 62471: 2006." Photobiological safety of lamps and lamp systems. Geneva: IEC (2006).
      Lockley, Steven W., George C. Brainard, and Charles A. Czeisler. "High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light." J Clin Endocrinol Metab 88.9 (2003): 4502-4505.
      Lockley, Steven W., et al. "Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans." SLEEP 29.2 (2006): 161.
      Longcore, Travis, et al. "Tuning the white light spectrum of light emitting diode lamps to reduce attraction of nocturnal arthropods." Philosophical Transactions of the Royal Society of London B: Biological Sciences 370.1667 (2015): 20140125.
      Menzel, R., and U. Greggers. "Natural phototaxis and its relationship to colour vision in honeybees." Journal of Comparative Physiology A 157.3 (1985): 311-321.
      Lucas, Robert J., et al. "Irradiance Toolbox."
      Lucas, Robert J., et al. "How rod, cone, and melanopsin photoreceptors come together to enlighten the mammalian circadian clock." Progress in brain research 199 (2011): 1-18.
      Lucas, Robert J., et al. "Measuring and using light in the melanopsin age." Trends in neurosciences 37.1 (2014): 1-9.
      Lund, D. J., J. Marshall, and J. Mellerio. "A computerized approach to transmission and absorption characteristics of the human eye." CIE. Vol. 203. 2012.
      Rahman, Shadab A., et al. "Diurnal spectral sensitivity of the acute alerting effects of light." Sleep 37.2 (2014): 271-281.
      Rea, Mark S., et al. "Circadian light." Journal of circadian rhythms 8.1 (2010): 2.
      Spitschan, Manuel, Bierman eyelid from the Silent Substitution Toolbox, GitHub, https://github.com/spitschan/SilentSubstitutionToolbox/tree/master/HumanEyelidTransmittance
      van der Lely, Stéphanie, et al. "Blue blocker glasses as a countermeasure for alerting effects of evening light-emitting diode screen exposure in male teenagers." Journal of Adolescent Health 56.1 (2015): 113-119.
      Zeitzer, Jamie M., et al. "Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression." The Journal of physiology 526.3 (2000): 695-702.
      Zeitzer, Jamie M., et al. "Temporal dynamics of late-night photic stimulation of the human circadian timing system." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 289.3 (2005): R839-R844.