Your Piece of Sky: Perception and Measurement of Daylight
(2023) , 14 pages
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- Authors
- Abstract
- Your Piece of Sky aims to bridge the gap between subjective and objective methods of gathering data about daylight and to translate information across disciplines. The project assessed the temporal variations of daylight in colour, spectrum and intensity for a selected 'piece of sky’ by comparing measurements with human perception. A piece of sky including Le Grammont and Mont-Blanc was selected during the Interdisciplinary Summer School “Measuring Light and Illumination” at Chexbres, Switzerland in August 2022. The following measurements were taken four times a day, across three consecutive days: the spot-luminance, spectral irradiance, and HDR image-based luminance maps. Through these twelve instances, the same piece of sky was painted on a 10x10cm canvas with oil paint. A comparison based on visual appreciation between the paintings, tone-mapped HDRs, luminance maps, and representative spot colour (derived from spectral irradiance) showed similar findings between the methods. Further analysis of dominant RGB colours in the scanned paintings and the tone-mapped HDR images showed a large spread of colour coordinates on the CIE 1931 colour space. After segregation to sky and ground parts, the coordinates for the ‘sky-only’ part ranged between 5000-8000K, matching the perceived sky colour and the measurements; whereas the ‘ground-only’ parts showed greater spread in CCT. Using measured spectral irradiance data, the M/P ratio and respective CCT through the instances showed a positive correlation (R2 = 0.896), and the luminance-to-CCT relationship aligned with the research by DiakiteKnoop for the instances taken in the clear-sky conditions. A key finding was that daylight has drastic temporal variations influenced by weather and time of day, and these variations model the spatial context with different visual clarity and detail. Under photopic vision, changes in sky colours were more noticeable in paintings than in the sky’s extreme variations in luminance. This phenomenon could be explained through eye adaptation.
- Affiliations
Citations
Monika Krześniak, Maskarenj, M., & Nils Voerste. (2023). Your Piece of Sky: Perception and Measurement of Daylight. Manuel Spitschan, Anna Biller. https://hdl.handle.net/2078.5/104935