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Sky Component
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Introduction#
The sky component analysis measures the ratio of direct illuminance from a sky between a point on an unobstructed horizontal surface and an analysis point. It can be run with different sky types but most common is the CIE Overcast sky. The analysis is called Vertical Sky Component (VSC) when run with an analysis point sampled on a vertical surface using the CIE Overcast sky.
The sky component can be measured on windows in the facade of a building in order to determine the potential of using daylight to light its interior.
Set Up#
The analysis can run either using a temporary scene or a static scene where geometry has been added prior to running the analysis.
Geometry Group#
The sky component analysis requires at least one geometry group in order to run. It either has to be supplied through the scene objects parameter, if the analysis is running on a temporary scene, or added to a static scene prior to running the analysis.
Analysis Points#
The analysis points specify both the location and the orientation of where the sky component should be evaluated. An analysis point is usually created on a surface using the normal of the surface as the analysis point direction.
Sky Type#
The sky type specifies the distribution of luminance over the hemisphere.
CIE Overcast Sky - Higher luminance towards zenith
CIE Uniform Sky - Uniform luminance across the sky
Visibility Mask#
The visibility mask can be used to exclude geometry groups from the analysis. This can be useful when the same scene is used for multiple analyses that require different geometric compositions.
Results#
The analysis will output a sky component ratio for each analysis point. The ratio can span from 0 for a fully obstructed point to 1 for an unobstructed horizontal point. The UK Building Research Establishment (BRE) has specified guidelines for the vertical sky component where a ratio of 0.27 is recommended for good potential to light a space using daylight.
