ISO/CIE 15469

2025-07-30
ISO/CIE FDIS 15469:2025(en)
CIE
Secretariat: CIE
Date:
Spatial distribution of daylight — CIE standard general sky
Répartition spatiale de la lumière du jour — Ciel général normalisé CIE
FDIS stage
ISO #####-#:####(X/CIE FDIS 15469:2025(en)
© ISO/CIE 2025
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ISO/CIE FDIS 15469:2025(en)
Contents
Foreword . iv
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
4 Relative sky luminance distribution . 3
5 Standard parameters . 5
6 Traditional overcast sky . 8
Annex A (informative) Derivation of the Standard Sky . 11
Bibliography . 12

Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms, definitions, symbols and abbreviations . 1
3.2 Symbols . 2
4 The relative sky luminance distribution . 3
5 Standard parameters . 4
6 The traditional overcast sky . 7
Annex A (informative) Derivation of the Standard Sky . 10
Bibliography . 11

© ISO /CIE 2025 – All rights reserved
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Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
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The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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This document was prepared by International Commission on Illumination (CIE) Technical Committee 3-15,
Spatial Distribution of Daylight,), in cooperation with Technical Committee ISO/TC 274, Light and lighting.
This first edition of ISO/CIE 15469 cancels and replaces the second edition of ISO 15469:2004/CIE S 011:2003,
which has been technically revised.
The main changes are as follows:
— — this document replaces CIE S 011:2003;
— normative references updated;
— — Clause 3 updated;
— — 3 updated;
— text added to Clauses 55 and 7;
— — keys written for Figures 1, 2, 3 and 4;
— — keys written for Figures 1, 2, 3 and 4;
— Bibliography updated;
— — minor editorial changes.
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ISO/CIE FDIS 15469:2025(en)
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.
© ISO /CIE 2025 – All rights reserved
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Introduction
The luminance distribution of the sky depends on weather and climate, and it changes during the course of a
day with the position of the sun. This document lists a set of luminance distributions which model the sky
under a wide range of conditions, from the heavily overcast sky to cloudless weather. It is intended for two
purposes:
a) a) to be a universal basis for the classification of measured sky luminance distributions;
b) b) to give a method for calculating sky luminance in daylighting design procedures.
This document defines relative luminance distributions: the luminance of the sky at any point is given as a
function of the zenith luminance. For daylighting calculation purposes, it may be used with values of zenith
luminance or of horizontal illuminance to obtain absolute luminance distributions.
This document incorporates both the CIE Standard Clear Sky and the CIE Standard Overcast Sky, which are
treated as particular cases of the General Sky. The Overcast Sky is retained as a separate formula because there
are many calculation procedures that embody the mathematical formulation of this particular distribution.
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ISO/CIE FDIS 15469:2025(en)
Spatial distribution of daylight — CIE standard general sky
1 Scope
This document specifies a set of outdoor daylight conditions linking sunlight and skylight for theoretical and
practical purposes.
The luminance distributions given have the following characteristics.
a) a) They are symmetrical about the solar meridian and are functions of the angular distance, Z ,
s
between the sun and the zenith.
b) b) They are defined by smooth continuous functions. Such distributions are typical of cloudless
skies and of those where the cloud cover is homogeneous. They provide an approximation to skies of
broken cloud that is sufficiently accurate for many practical daylight calculation purposes.
c) c) The relative luminance at any point in the sky depends on the angle, χ, between that sky
element and the sun, and on the angle, Z, between the sky element and the zenith. It is given in terms of
two functions: the relative scattering indicatrix, f(χ), and the luminance gradation between horizon and
zenith, φ(Z).
NOTE See Annex AAnnex A for the derivation of the CIE Standard General Sky.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
CIE S 017, ILV: International Lighting Vocabulary
ISO 80000--7, Quantities and units — Part 7: Light and radiation
3 Terms, definitions and symbols
3.1 Terms, definitions, symbols and abbreviations
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
CIE maintains a terminology database for use in standardization at the following address:
— — ILV: International Lighting Vocabulary: available at https://cie.co.at/e-ilvhttps://cie.co.at/e-ilv
© ISO /CIE 2025 – All rights reserved
ISO/CIE FDIS 15469:2025(en)
3.2 Symbols
For the purposes of this document, the following symbols apply. For quantities and units, CIE S 017 and ISO
80000-7 shall apply.
a, b luminance gradation parameters
α azimuth of a sky element (clockwise from north) [rad]
α azimuth of the sun (clockwise from north) [rad]
s
c, d, e scattering indicatrix parameters
χ shortest angular distance between
...