scope:

This Guide provides the following:

1) An explanation of the CIE Standard General Sky concept and its simplified use by general practitioners, together with an appropriate list of generally available references.

2) A recommended procedure for the classification and frequency analysis of skies usable for various design or energy use purposes, with a recommended procedure to derive absolute values from the values expressed in relative units of the ISO/CIE Standard, i.e. luminance in cd⋅m⁻² and illuminance in lx, when necessary for supplementary electric lighting or any control purposes.

3) Examples of production of CIE sky type frequencies around the world as annual daylight profiles (Daylight Reference Years) using the application of all or several standard skies.

4) The possibilities to simulate sky luminance distributions in artificial sky facilities.

This Guide is intended to be used by both, users of sky models (for daylight estimation and lighting simulation purposes) as well as the developers of computer software that use the models to estimate the availability of daylight in their simulation models.

Users are those who

1) are interested in the range of sky luminance patterns that can be modelled by the SSLD models presented in the ISO/CIE Standard, and

2) must choose a particular model or series of models, for use in a computation of daylight availability or a lighting simulation to match their locale.

Developers are those who

1) are developing building simulation software systems that implement the SSLD model equations, and

2) must ensure that their implementations are correct.

For practical use additional computations are required, for example:

1) The sun position must be determined from the local latitude, longitude, date and time, using a suitable Equation of Time, and

2) the zenith luminance can be determined by local measurements or estimated in relation to known local diffuse horizontal illuminance.