CIE-S-003-E-1996.pdf

4 Pl S Standard CIE S 003/E-I 996 Spatial Distribution of Daylight - CIE Standard Overcast Sky and Clear Sky Répartition spatiale de la lumière du jour - Ciel couvert et ciel serein normalisés CIE Räumliche Verteilung des Tageslichts - Bedeckter Himmel und klarer Himmel nach CIE genormt CIE Standards are copyrighted and shall not be reproduced in any form, entirely or partly, without the explicit agreement of the CIE. S 003/E CIE Central Bureau, Vienna Kegelgasse 27, A-I 030 Vienna, Austria UDC: 551 521. -í Descriptor: Solar radiation 628.9.021 Sunlight 681 -782.43 Photometers for global radiation measurement Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,- Spatial Distribution of Daylight - CIE Standard Overcast Sky and Clear S k y Contents Page Foreword II Introduction 1 Scope 2 Normative References 3 Symbols 4 Specification 4.1 CIE Standard Overcast Sky 4.2 CIE Standard Clear Sky Derivation of the Standard Skies 5.1 CIE Standard Overcast Sky 5.2 CIE Standard Clear Sky Practical Application o f the Standard Skies 6.1 CIE Standard Overcast Sky 6.2 CIE Standard Clear Sky 5 6 I 1 I 2 3 3 3 4 4 4 4 4 4 Annex A (informative) - References 5 Foreword Standards produced by the Commission Internationale d'Eclairage are concise documents on aspects of light and lighting that require a unique definition. They are a primary source of internationally accepted and agreed data which can be taken, essentially unaltered, into universal standard systems. This Standard has been prepared by Division 3 (Intenor Environment and Lighting Design) of the Commission Internationale de I'Eclairage and approved by the National Committees of the Commission. This Standard summarizes the results described in Proc. 13th Session of the CIE, Zurich, 1955, Vol. II, Part 3-2 on the Overcast Sky and in the publication CIE 22-1973 “Standardisation of luminance distribution on clear skies“. These definitions represent recommended standard outdoor natural daylight conditions which can be used in calculations, modelling and for the design and evaluation of interior daylighting. They represent two extreme cases. Other CIE reports, based on more recent research, will provide further guidance in selecting the most appropriate luminance distribution to perform calculations. II Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,- STD-CIE S 003/E-ENGL L77b 700bL45 0005b23 340 CIE S 003/E-I 996 Introduction The luminance distribution of the sky varies with weather and climate. This Standard defines two conditions which tend to occur under stable conditions and which may be taken as extreme cases. They are described by relative luminance distributions: the luminance of any point in the sky is given as a function of the zenith luminance. The “CIE Overcast Sky“ was originally prepared by CIE Technical Committee E-3.2 (Natural Daylight) and published as an official recommendation in 1955 I. The “CIE Clear Sky“ was published by CIE Technical Committee 4.2 (Daylight) in 1973 Z. The two documents are now superseded by this Standard. Background information and further details are described in a Technical Report on the spatial distribution of daylight 3 . 1. Scope The Standard defines the relative luminance distributions of the CIE Standard Overcast Sky and the CIE Standard Clear Sky as outdoor daylight conditions for theoretical and practical purposes. (.I) CIE Standard Overcast Sky represents the sky luminance pattern associated with deep layers of stratus clouds I. Under these conditions the sun's disk is usually invisible from the ground. The luminance distribution of the Standard Overcast Sky is a function only of the angle of elevation above the horizon. It is therefore symmetrical about the zenith and independent of the sun's position. The luminance of clouds is affected by light reflected from the ground surface. The Standard Overcast Sky is based on the assumption of a dark terrain. It should not be applied when the ground is covered with snow or when the surface consists mainly of other material of high reflectance, such as white sand. ( 2 ) CIE Sfandard Clear Sky represents cloudless conditions 2 . The luminance of the sky depends on both the angle of elevation and the position of the sun. It is symmetrical about the solar meridian. The luminance of a cloudless sky is affected by pollution and by other sources of atmospheric particles. The Standard Clear Sky is given in two forms: for application to Clean rural conditions and for polluted or industrial atmospheres. 2. Normative References The following standards contain provisions which, through reference in this text, constitute provisions of this Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of CIE, IEC and IS0 maintain registers of currently valid international standards. 1 Publication CIE 17.4-1 987: International Lighting Vocabulary, 4th ed. (joint publication IEC/CIE) 2 IS0 31-1992: Quantities and units, Part 6: Light and related electromagnetic radiations 3 Publication CIE 16-1970: Daylight 4 Publication CIE 110-1994: Spatial distribution of daylight - Luminance distributions of various reference skies. 1 Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,- CIE S 003/E-1996 3 . List of Symbols For the purposes of this Standard, the following symbols apply: azimuth angle of a sky element (clockwise from north) rad azimuth angle of the sun position (clockwise from north) rad illuminance from an unobstructed clear sky on a horizontal surface lx illuminance from an unobstructed overcast sky on a horizontal surface Ix angle of elevation of a sky element above the horizon rad angle of elevation of a sun position above the horizon rad relative diffusion indicatrix of clear rural atmosphere relative diffusion indicatrix for polluted atmosphere transmission function of the atmosphere angle between the sun and the sky element rad clear sky luminance of a sky element cd/m2J overcast sky luminance of a sky element cd/m2 clear sky luminance at the zenith cd/m* overcast sky luminance at the zenith cd/m2 For quantities and units used see Normative References 1 - + 0 , 3 cos2(; -ys) ' ) = 0,27385 * Note: The value of 2,45 is for clear rural atmospheres, in some countries, e.g. Germany, a value of 5 is considered, which is more typical for an industrial environment. 3 Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,- - STD*CIE S 003/E-ENGL 177b = SOObL'i5 0005bZb 05T CIE S 003/E-1996 5. Derivation of the Standard Skies 5.1 CIE Standard Overcast Sky This sky was originally presented in a paper by Kahler in 1908 4 and tested by Moon and Spencer in 1942 ES using analysis of measurements by Kimball in the early 1920's. After two further series of measurements, in Southern England and in Sweden, it was confirmed that this formula was applicable to densely overcast skies, at least at middle latitudes. It was adopted as an official recommendation by CIE Technical Committee E-3.2 in i955 l. 5.2 CIE Standard Clear Sky The original form of this sky was proposed by Kittler at the meeting of CIE Technical Committee E-3.2 at Newcastle upon Tyne in 1965. It was also presented in a paper to the CIE Intersessional Conference on Sunlight S I . This conference included detailed discussion on the scientific basis of the standardization and also comparisons between calculated and measured luminance distribution data. The additional indicatrix, P ( 5 ) . by Gusev for industrial and other polluted atmospheres was included in the draít standard at the 1969 CIE intercessional meetings in Bratislava and Cmolenice 7. The Linke Turbidity Factor is described in 8. Further background literature was published in 31. 6. Practical application of the Standard Skies 6.1 CIE Standard Overcast Sky This sky may be used to calculate daylight factors under densely overcast skies associated with stable conditions of low illuminance *. If the horizontal illuminance from an unobstructed sky is known, the interior illuminance may be found from this and the daylight factor. If the absolute zenith luminance is known, the corresponding horizontal illuminance, E%, from the CIE Standard Overcast Sky is given by: 6.2 CIE Standard Clear Sky Interior luminances and illuminances on a cloudless day can be calculated when the absolute zenith luminance and the direct solar illuminance are known 3 . Under cloudless conditions the lighting conditions may be stable, varying only with the sun's position. The interior values enable psychological effects of the daylight environment to be assessed. Estimates can be made also of glare and of energy savings. _ I _ * Note: It has been shown that the model can also be used for the tropical overcast sky SI. 4 Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,- CIE S 003/E-1996 Annex A (informative) References Natural daylight. Officiai recommendation, Compte Rendu CIE 73 Session 1955, Committee (E-3.2) Vol.ll, part 3-2, Il-IV & 35-37 (1955). Publication CIE 22-1 973 (TC-4.2), “Standardization of Luminance Distribution on Clear Skies“ (1973). Publication CIE 11 0-1994, “Spatial distribution of daylight - Luminance distributions of various reference skies'' (1 994). Kahler, K., “Flächenhelligkeit des Himmels und Beleuchtungsstärke in Räumen“, Mefeorol. Zejfschf., 25, 52-57 (1908). Moon, P. and Spencer, D.E., “Illumination from a non-uniform sky“, /um. Engng. Kittler, R., “Standardization of outdoor conditions for the calculation of daylight factor with clear skies“, Proc. the CIE International Confefeme on Sunlight in Buildings, Bouwcentrum International, Rotterdam, 273-285 (1 967). Gusev, N.M., Personal communication to “CIE Clear Sky Standard“ Reporter, 1968. Archived at CIE TC 3-15 material at CIE CB. Linke, F., Boda K., “Vorschläge zur Berechnung des Trûbungsgrades der Atmosphäre“, Mefeoro/, Zeifschr. 39,161-166 (1922). Sastri, V.D.P., Manamohanan, S.B. and Das, S.R., “Luminance distribution of Tropical Overcast and Clear Skies“, Journal of Opfics 2,28-32 (1 973). (N.Y.), 37, 707-726 (1942). 5 Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,- STDOCIE S 003/E-ENGL L99b 9006345 0005b28 722 CIE S 003/E-1996 CIE Central Bureau Kegelgasse 27 A-1030 Vienna, Austria Tel.: +43 I - 714 31 87 O Fax: 4-43 1 - 713 08 38 18 E-mail: ciecbping.at Copyright International Commission on Illumination Provided by IHS under license with CIELicensee=IHS Employees/1111111001, User=leee, leee Not for Resale, 11/24/2007 08:55:18 MSTNo reproduction or networking permitted without license from IHS -,-,-