Standardization of Luminance Distribution on Clear Skies

CIE 022-1973
978 3 900734 52 7

Superseded by Spatial Distribution of Daylight - Luminance Distributions of Various Reference Skies

CIE 110-1994

The terms of reference of TC 3-09 were "to study standard reference skies between the two skies already standardized, clear sky and overcast sky, and to propose a method of composing average and mean skies". Accordingly, this technical report reviews studies on various sky luminances and specification of reference skies, with a method of composing average sky and mean sky as an appendix. Several reference skies including the average sky and mean sky are given, definitions and various studies on these sky luminances are introduced, with a bibliography, in three appendices.

Although several kinds of average and mean skies have been proposed in Europe, USA and Japan since 1981, their definitions and the methods of composing them were not standardized. Also the two CIE Standard skies (Clear sky and overcast sky) are reviewed in the present publication, thus CIE 22-1973 is now outdated and withdrawn. The standardization of reference skies between the two standard skies was left to a new technical committee, TC 3-15 (Standardization of intermediate sky luminance), which was formed at the CIE Venice Session in June 1987. In this report a references sky means a clearly defined sky to be used for daylighting design and calculation. For example, one reference sky is the uniform sky which has been used for a number of theoretical applications and for certain design purposes. The skies treated in this report do not include direct sunlight, though the BRE average sky developed by Littlefair consists of two components, direct sunlight and the sky.

In order to estimate annual energy consumption of electrical lighting, the effect of direct sunlight should be taken into consideration in calculating illuminance on the interior working plane, whether this is done for every weather condition or for a certain average condition. Hence, each standard sky luminance has to be combined with a standard direct sunlight illuminance. These items are to be decided in another technical committee in future, but a proposal is tentatively shown.

The report is written in English, with a short summary in English, French and German. It contains contains 33 pages, 10 figures and 2 tables.

The following members of TC 3-09 took part in the preparation of this technical report:

  • S. Aydinli, Germany
  • P. Chauvel, France
  • R. Dogniaux, Belgium
  • D. Kendrick, Australia
  • R. Kittler, Slovakia
  • P. Littlefair, Great Britain
  • K. Matsuura, Japan (Chair)
  • T. Nagata, Japan
  • H. Nakamura, Japan
  • E. Ne'eman, Israel
  • S. Selkowitz, USA


003-1996 CIE Standard Overcast Sky and Clear Sky

Superseded by Spatial Distribution of Daylight - CIE Standard General Sky

Joint ISO/CIE Standard

ISO 15469:2004 (E)/CIE S 011/E:2003

CIE has published the Standard "CIE S003 Spatial distribution of daylight - CIE standard overcast sky and clear sky" in 1996. Since then further types of skies were examined and an international consensus was reached on their luminance distribution and standardization.

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 standard 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:

i. to be a universal basis for the classification of measured sky luminance distributions

ii. to give a method for calculating sky luminance in daylighting design procedures.

This Standard 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 Standard 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.

This present Standard replaces CIE S 003 - 1996 "Spatial distribution of daylight - CIE standard overcast sky and clear sky" and ISO 15469:1997.

This standard has been approved by CIE and by ISO.

The following members of CIE TC 3-15 "Sky Luminance Models" took part in the preparation of this Standard:

  • Y. Uetani (Chairman), Japan
  • S. Aydinli, Germany
  • A. Joukoff, Belgium
  • J.D. Kendrick, Australia
  • R. Kittler, Slovakia
  • Y. Koga, Japan
  • K. Matsuura, Japan
  • T. Nagata, Japan
  • H. Nakamura, Japan
  • M. Oki, Japan
  • R. Perez, USA
  • P.R. Tregenza, Great Britain
  • P. Valko, Switzerland