The main scientific achievement of the project were the development of a framework to generate location-specific spectral skies and the creation of an open-source dataset containing measured spectral daylight measurements. Currently, measuring spectral sun and sky data requires expensive instrumentation and maintenance, limiting the availability of such data to only a few select locations worldwide.
A close interdisciplinary collaboration with the atmospheric scientist at the German Weather Service’s (DWD) Meteorological Observatory at Lindenberg (DWD-MOL) was set up to implement and validate this framework. The framework modifies standard atmospheric files pre-packaged within physics-based radiative transfer programs like libRadtran by incorporating location-specific atmospheric constituents' data (aerosols, water vapor, and ozone), which are commonly obtained through measurements or satellite observations. This modification allows for the generation of high accuracy, location-specific spectral daylight data that can be integrated into various spectral daylight prediction platforms. A comprehensive description of the framework and its validation for clear skies will be available in the Institute of Physics (IOP’s) golden open-access proceedings of Journal of Physics: Conference Series as: Balakrishnan, P., Knoop, Martine., Doppler, Lionel (2023). "A Framework for Generating Local Spectral Skies for Spectral Daylight Simulations."
The framework was presented at the CISBAT: The Built Environment in Transition International Conference 2023 for the building science community. Furthermore, within the atmospheric science community, the framework was adapted for radiative closure by the scientist at DWD-MOL. They presented this work at the European Meteorological Society's Annual Meeting 2022 in Bonn, Germany. The presentation is indexed and available as follows: Doppler, L., Wacker, S., Mäusle, S. J., Riedel, J., & Balakrishnan, P. (2022). Radiative closure (simulation↔ measurements) with a complete input/output measurement dataset of supersite Meteorological Observatory Lindenberg (Germany).https://doi.org/10.5194/ems2022-262.
A second outcome of this project was the release “skyspectra” an opensource worldwide spectral daylight data package. A worldwide campaign to collect spectral daylight measurements from various locations was initiated during the 29th quadrennial session of the International Commission of Illumination (CIE) and a CIE technical committee (CIE TC 3-60) was established to investigate the spectral characteristics of daylight in 2021. The data collected as part of the global campaign and through the efforts of CIE TC 3-60 includes spectral daylight information from both long-term measurement sites and specific periods or experiments. Spectral daylight data from 7 of these locations has been standardised and made publicly available as "skyspectra," which can be accessed as Balakrishnan, P. (2023). SKYSPECTRA: an open-source global spectral daylight data package (skyspectra-1.0.0) on Zenodo at
https://doi.org/10.5281/zenodo.8147546(öffnet in neuem Fenster).
The dataset was formally introduced at a conference, and an accompanying paper that elucidates the data collection process and its organisation into a standardised framework is available open-source within the conference proceedings. The paper is indexed and available as follows: Balakrishnan, P., Diakite-Kortlever, A., Dumortier, D., Hernández-Andrés, J., Kenny, P.4 Maskarenj, M, Pierson, C, Thorseth, A, Xue, P, Knoop, M. (2023). "SKYSPECTRA: An Open-Source Data Package of Worldwide Spectral Daylight." Presented at the 30th session of the CIE Conference, September 15-23, 2023, Ljubljana, Slovenia.
awaiting DOI to be active(öffnet in neuem Fenster)The project also involved the measurement of spectral characteristics within built environments and the reconstruction of 3D environments. To identify typical urban environments and materiality, a large-scale study was conducted to analyse the visual, spectral, and colorimetric attributes of 334 facades in seven different Berlin neighbourhoods. A GitHub repository has been established and is set to be publicly released next year, with proper attribution to the DAYCOP funding source. Two other studies were planned to assess the seasonal effects of different urban settings on indoor daylight conditions. One study examined a room overlooking trees, while the other focused on a room facing a white reflective facade. The studies monitor photometric, colorimetric, and spectral characteristics, across the seasons. Ongoing efforts in the project involve the representation of the reconstructed 3D environments as virtual reality (VR) scenes for subjective evaluations.
The results and findings from the DAYCOP project will be incorporated into the technical report of the CIE TC 3-60 planned for completion in 2026. This report will offer comprehensive guidelines and recommendations regarding geographical, seasonal, and time-of-day variations in the spectral characteristics of daylight. CIE technical reports serve as pivotal resources reaching policymakers, lighting industry professionals, and research scientists involved in shaping lighting standards and practices worldwide.
