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Author (up) Spitschan, M.; Aguirre, G.K.; Brainard, D.H.; Sweeney, A.M. url  doi
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  Title Variation of outdoor illumination as a function of solar elevation and light pollution Type Journal Article
  Year 2016 Publication Scientific Reports Abbreviated Journal Sci Rep  
  Volume 6 Issue Pages 26756  
  Keywords Skyglow; Measurements; light pollution; daylight; twilight; sky brightness; spectral irradiance; CIE  
  Abstract The illumination of the environment undergoes both intensity and spectral changes during the 24 h cycle of a day. Daylight spectral power distributions are well described by low-dimensional models such as the CIE (Commission Internationale de l'Eclairage) daylight model, but the performance of this model in non-daylight regimes is not characterised. We measured downwelling spectral irradiance across multiple days in two locations in North America: One rural location (Cherry Springs State Park, PA) with minimal anthropogenic light sources, and one city location (Philadelphia, PA). We characterise the spectral, intensity and colour changes and extend the existing CIE model for daylight to capture twilight components and the spectrum of the night sky.  
  Address Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA  
  Corporate Author Thesis  
  Publisher Nature Place of Publication Editor  
  Language English Summary Language English Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 2045-2322 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:27272736 Approved no  
  Call Number IDA @ john @ Serial 1464  
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Author (up) Walmsley, L.; Hanna, L.; Mouland, J.; Martial, F.; West, A.; Smedley, A.R.; Bechtold, D.A.; Webb, A.R.; Lucas, R.J.; Brown, T.M. url  doi
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  Title Colour As a Signal for Entraining the Mammalian Circadian Clock Type Journal Article
  Year 2015 Publication PLoS Biology Abbreviated Journal PLoS Biol  
  Volume 13 Issue 4 Pages e1002127  
  Keywords Animals; biology; color; circadian disruption; animal models; mouse models; Suprachiasmatic Nucleus; Photoperiod; twilight  
  Abstract Twilight is characterised by changes in both quantity (“irradiance”) and quality (“colour”) of light. Animals use the variation in irradiance to adjust their internal circadian clocks, aligning their behaviour and physiology with the solar cycle. However, it is currently unknown whether changes in colour also contribute to this entrainment process. Using environmental measurements, we show here that mammalian blue-yellow colour discrimination provides a more reliable method of tracking twilight progression than simply measuring irradiance. We next use electrophysiological recordings to demonstrate that neurons in the mouse suprachiasmatic circadian clock display the cone-dependent spectral opponency required to make use of this information. Thus, our data show that some clock neurons are highly sensitive to changes in spectral composition occurring over twilight and that this input dictates their response to changes in irradiance. Finally, using mice housed under photoperiods with simulated dawn/dusk transitions, we confirm that spectral changes occurring during twilight are required for appropriate circadian alignment under natural conditions. Together, these data reveal a new sensory mechanism for telling time of day that would be available to any mammalian species capable of chromatic vision.  
  Address Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom  
  Corporate Author Thesis  
  Publisher PLOS Place of Publication Editor  
  Language English Summary Language English Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1544-9173 ISBN Medium  
  Area Expedition Conference  
  Notes PMID:25884537 Approved no  
  Call Number IDA @ john @ Serial 1152  
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