"The Colour(s) of the Sky - Bridging the Theory and Practice" by Aicha Diakite
Researcher and lighting engineer
Presentation from the 8th VELUX Daylight Symposium that took place in Paris on 9 October 2019. For more information please visit http://thedaylightsite.com & https://www.velux.com/veluxdaysinparis
The spatio-temporal variability of daylight in intensity and colour is beneficial for smart, healthy and energy efficient daylighting strategies. While there is a substantial amount of studies on the non-uniformity of the photometric attributes of the sky, relatively little is known about its spectral distribution. Nevertheless, to appropriately include this dynamic natural light source in lighting and product design, the spectral characteristics of daylight need to be measured and described accurately. To do this, ground-based spectral sky measurements of high precision over long period of time have been conducted. However, spectrally and spatially resolved measurements are cost- and labour intensive, which results in only three institutes worldwide collecting spatially resolved spectral daylight data.
The objective of the presentation is to demonstrate how to transform the detailed spectral and directional measurements to a simplified assessment of the colour(s) of the sky, to ensure applicability in the design process and the development of lighting products. For some applications information on colour temperature (CCT) or colour point (chromaticity coordinate x,y) already suffices. Other applications might require spectral power distributions (SPD). The presentation will show how the SPD can be obtained from either CCT or x,y. The then acquired spectrally resolved daylight data can be weighted with any weighting function. Thus, a representation of highly detailed measurements of daylight in one single value, its CCT, is enough.
This offers possibilities in the design process, as for example used in spectral sky models, which include CCTs in 145 directions. Lighting designers and architects can work with the colour(s) of the light in different orientations, as well as with the detailed spatially and spectrally resolved data to design smart, healthy and energy efficient daylighting solutions. As a colour point measurement can provide spectral information, light dose measurements in daylight studies on non-visual, ipRGC-influenced light (IIL) responses, can be conducted with colour sensors. This type of sensors can be implemented in lighting control systems that support IIL effects. Additionally, due to their light weight, colour sensors can be mounted on drones to monitor, map and measure daylight in built environments more flexibly. In summary, this presentation will show how years of detailed measurements can now be used in a practicable manner to consider the colour(s) of the sky in the design process and product development.
Aicha Diakite is a researcher and lighting engineer working in the field of daylighting. She studied Electrical Engineering at TU Berlin (Germany) and Poznan University of Technology (Poland). She went on to study Architecture and Industrial Design at UNAM (Mexico), where she received the Postgraduate Architectural Lighting Design Diploma. Aicha has received several awards for her work including the H.-J.-Helwig-Prize by the German Lighting Technology Association, the VDI Recognition by the Association of German Engineers, and the Hans-Peter-Willumeit-Award by the Foundation Committee of the Center of Human-Machine Systems. She is currently working at the Department of Lighting Technology at the TU Berlin having previously served in Lighteam, Kardorff Ingenieure Lichtplanung, OSRAM and Hellux Construktions-Licht. Aicha is in the final stage to completing her PhD at the TU Berlin. Her research proposes new spectral sky models to enable the integration of daylighting strategies into the design of urban structures that support people’s well-being.