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A thorough analysis of sky distributions can help in the prediction of daylight patterns and thus provides a good understanding of architectural window and building envelope design. This paper introduces three methods of analysis for sky distributions, namely the relative indicatrix and gradation classification, and two other independent methods established by Kittler and Tregenza. All these three methods were verified for their feasibility for analysing the extreme daylight conditions in Singapore, which is located at the equator. The most suitable approach, from Tregenza, was eventually adopted in analysing the measured data from Singapore IDMP station. The prediction of frequent sky patterns in Singapore was based on the CIE Standard General Skies, as well as a complete version considering all 36 theoretical sky types.

a b s t r a c tThis study presents optimization approaches by a recent Climate-Based-Daylight-Modeling tool, EvalDRC, to figure out the necessary area for a daylight redirecting micro-prism film (MPF) while minimizing the glazing area. The performance of a window in terms of spatial Daylight Autonomy (sDA) is optimized by its geometry and optical properties. Data implemented in simulation model are gathered through on-site measurements and Bidirectional-Scattering Distribution Function (BSDF) goniomeasurements. EvalDRC based on Radiance with a data driven model of the films' BSDF evaluates the window configurations in the whole year. The case to achieve an sDA of at least 75% is a South-facing window of a classroom in Switzerland. A window zone from 0.90 m to 1.80 m height provides view to the outside. The upper zone from 1.80 m to 3.60 m is divided into six areas of 0.30 m height in three optimization approaches including the operation of sunshades as well. First, the size of the clear glazing is incrementally reduced to find the smallest acceptable window-to-wall ratio (WWR). Second, microprism films are applied to an incrementally varying fraction the initial glazed area to determine the minimum film-to-window ratio (FWR). Finally, both approaches are combined for a minimum FWR and WWR. With clear glazing and WWR of 75%, the sDA of 70.2% fails to meet the requirements. An sDA of 86.4% and 80.8% can be achieved with WWR 75%, FWR 1/9 and WWR 50%, FWR 1/2 respectively. The results demonstrate the films' potential to improve the performance of windows with reduced WWR.

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