Scattered sunlight determining sky luminance patterns

doi:10.1016/j.rser.2016.05.012

2016-09-01

PRE

Richard Kittler

Stanislav Darula *

DOI：10.1016/j.rser.2016.05.012

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摘要

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During the first daylight photometry studies in the 18th Century three fundamental source types of daylight were characterised as direct sunlight, clear sky luminance distribution and overcast sky luminance uniformity. For minimum illumination and simplicity the last became the basic state to determine computational methods and practical graphical tools to evaluate daylight distribution especially in poorly naturally lit interiors. The simultaneously present sunlight and skylight under cloudless or cloudy conditions attracted the research of sky luminance distributions caused by the scattering of sunbeams within the atmosphere. The arbitrary real sky luminance patterns influenced by air molecule and aerosol turbidity as well as cloudiness were studied and measured to determine the relatively complex their changes. The historical search after the interrelated definition and mathematical expression of gradation and scattering indicatrix functions is explained in the gradually evolving progress in this paper. Recently in sustainable solar energy utilisation and daylighting studies via building apertures and photovoltaic panels take into account also radiance and luminance gains from the sky vault under any weather conditions. The luminance distribution on homogeneous sky types is today based on mathematically defined ISO/CIE standards of relative gradation and indicatrix functions in the range between overcast and cloudless skies. The review of the development and the different methodologies of categorising typical sky luminance patterns is discussed and summarised in this paper. (C) 2016 Elsevier Ltd. All rights reserved.

Keyword:

Sky luminance/radiance patterns

Sunlight scattering indicatrix

Sky luminance gradation

Standard homogeneous sky luminance distribution