Pro Lite Technology

Whole Sky Luminance Mapping

Luminance Variations in the Sky Over Dublin

ProMetric™ imaging photometer helps improve lighting inside buildings

The University College Dublin Energy Research Group (UCD ERG), part of the UCD School of Architecture, Landscape and Civil Engineering, Dublin, Ireland, has been actively pursuing research in the field of sustainable building design and energy efficiency for more than 30 years. As part of its on-going research interests it has been developing a technique to capture and reproduce whole-sky luminance distributions of various real and dynamic skies typical of maritime climates. The results will be used in the analysis and design of visual environments and in assessing solar energy availability in buildings and urban spaces.

Theoretical models of sky luminance used in the simulation and modelling of the built visual environment do not accurately represent the reality observable under everyday skies and do not serve the demands of visual comfort research. It is unlikely that any theoretical model will ever do so due to the uniqueness of each instance of sky luminance distribution. Instead, research at UCD ERG looked for ways to more accurately represent real sky luminance distributions that would allow the true dynamic of real daylight to be applied in design and advanced daylight research.

The research looked to Imaging Luminance Measuring Devices, or ILMD’s, such as the Radiant Imaging range to see if they might be used to capture at high resolution the detailed dynamic and variability of real sky luminance distributions to be later reproduced in a purpose-built artificial sky and through computer modelling and simulation.

The Radiant Imaging ProMetric™ PM-1400 was selected based on a number of criteria including the high dynamic range of the CCD sensor (Kodak KAF 1001E) due to its relatively large pixel dimensions and electron capacitance, its full-frame size for use with a 180° circular fisheye lens, 100% sensor optical fill-factor and the co-operation of Radiant Imaging to modify the lens mount to incorporate ND filters for exposure control.

The resulting images represent 693,000 simultaneous measurements of sky luminosity across its hemisphere equating to a resolution of 9 x10-6 steradians per pixel. Images are captured every five seconds which, collectively, provide for a very accurate animated representation of dynamic sky luminosity.

UCD Heliodon Artificial Sky

The research is currently working to use an artificial sky (shown above) to reproduce a collection of ‘typical’ occurrences to facilitate architectural and urban design. Ireland’s first artificial sky provides a facility that allows researchers and designers to simulate daylight conditions within and around buildings, using scale models. The sky can reproduce a full range of Commission Internationale de L’Eclairage (CIE) standard overcast and clear skies with an integrated heliodon. The artificial sky is used in the investigation of internal daylight distribution, urban solar access and overshadowing analysis, and the test and measurement of advanced window and shading systems.

Further reference: Kenny, P., Olley, J., Lewis, J. O. (2006). Whole-Sky Luminance Maps from Calibrated Digital Photography, in Eurosun2006, Glasgow. Pro-Lite gratefully acknowledges Paul Kenny (paul.kenny@ucd.ie) for his permission to publish this article. Paul is Lead Researcher and Director of UCD Energy Research Group. For further information on ProMetric CCD imaging photometers, click here.

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