September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
How fast does the color of daylight change?
Author Affiliations & Notes
  • Ruben Pastilha
    Newcastle University
  • Gaurav Gupta
    Newcastle University
  • Naomi Gross
    Newcastle University
  • Anya Hurlbert
    Newcastle University
  • Footnotes
    Acknowledgements  This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 765121.
Journal of Vision September 2021, Vol.21, 2740. doi:
  • Views
  • Share
  • Tools
    • Alerts
      This feature is available to authenticated users only.
      Sign In or Create an Account ×
    • Get Citation

      Ruben Pastilha, Gaurav Gupta, Naomi Gross, Anya Hurlbert; How fast does the color of daylight change?. Journal of Vision 2021;21(9):2740.

      Download citation file:

      © ARVO (1962-2015); The Authors (2016-present)

  • Supplements

Natural illumination undergoes changes in hue and saturation associated with sun elevation, yet people do not seem to perceive these changes directly. Previously, we measured speed detection thresholds of smooth changes in daylight metamers and showed that discrimination of chromaticity changes depends on the Correlated Color Temperature (CCT) of the base (adapting) illumination: cool-changes become less noticeable for progressively warmer base lights and vice-versa (Pastilha et al., 2020). Here we analyze temporal variations of real daylight. We aim to determine the velocity range of daylight chromaticity changes and compare it to the previously found discrimination thresholds (Pastilha et al., 2020). We use databases of spectral irradiance measurements of outdoor downwelling light taken at regular intervals from dawn to dusk, at different locations in the northern hemisphere. Daily spectral data were collated by month. Estimates of the maximum velocity of daylight chromaticity changes for each month were obtained from smooth fits to the aggregated data, taking into account all possible CIELUV white points from the daylight locus. In all months and locations, the fastest CCT changes occur at sunset and sunrise, but speeds depend on day length and vary throughout the year. For a 2-year dataset from Granada, Spain (Hernández-Andrés et al., 2007), the largest velocity estimate is about 0.02 ΔEu*v*/s, occurring in January. Similar estimates (0.03 ΔEu*v*/s) are found for a 20-day dataset from Stanford, USA at the same latitude (37º) and month (DiCarlo & Wandell 2000). Note that here, concomitant changes in lux - which may be significant - are not considered. The maximum velocity of chromaticity change in daylight is much slower than the minimum illumination velocity discriminated by the observers in our previous experiments (0.5 ΔEu*v*/s), at least for these daylight measurements. These results suggest that outdoor CCT changes are too slow to be detected.


This PDF is available to Subscribers Only

Sign in or purchase a subscription to access this content. ×

You must be signed into an individual account to use this feature.