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Lookup NU author(s): Dr Cehao Yu, Ruben Pastilha, Professor Anya Hurlbert
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Natural daylight varies continuously in chromaticity and illuminance over multiple timescales, shaped by solar geometry, atmospheric conditions, and surface reflections. To quantify these dynamics, we measured 4512 directional spectra, yielding 752 complete light field samples across four days at two locations under diverse weather conditions. Diffuse and directional components of daylight were separated, revealing a consistent tripartite daily pattern: rapid chromatic shifts at dawn and dusk, and relative stability around midday. Directional illumination exhibited larger and faster variations, particularly under clear skies, while diffuse illumination remained comparatively stable but less regular, likely due to surface reflections. Psychophysical measurements of temporal chromaticity discrimination thresholds [1] show asymmetries in perceptual sensitivity: shifts toward cooler CCTs (∼1.2 ΔE/s) are more easily detected than shifts toward warmer CCTs (∼2 ΔE/s), when starting from a cool daylight CCT (10,000 K). Natural rates of change at dawn and dusk (up to ∼0.4 ΔE/s) are generally well below these perceptual thresholds, with only directional components under clear skies transiently approaching threshold visibility. These asymmetries may reflect functional dissociations between perceptual stability and circadian regulation, with non-visual pathways remaining sensitive to structured daylight changes even when conscious perception is suppressed.
Author(s): Yu Cehao, Pastilha Ruben, Hurlbert Anya
Publication type: Article
Publication status: Published
Journal: Journal of Physics: Conference Series
Year: 2025
Volume: 3128
Online publication date: 06/11/2025
Acceptance date: 22/09/2025
Date deposited: 01/01/2026
ISSN (print): 1742-6588
ISSN (electronic): 1742-6596
Publisher: IOP Publishing
URL: https://doi.org/10.1088/1742-6596/3128/1/012005
DOI: 10.1088/1742-6596/3128/1/012005
Notes: 6th London Imaging Meeting (LIM 2025) 09/09/2025 - 10/09/2025 London, United Kingdom https://iopscience.iop.org/issue/1742-6596/3128/1
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