Colorimetry - Part 2: CIE standard illuminants (ISO 11664-2:2007)

ISO 11664-2:2007 comprises ISO 10526:2007 and ISO 10526:2007/Cor.1:2008. Its technical content is identical to that of ISO 10526:2007. ISO 10526:2007/Cor.1:2008 changes the reference number of the standard from 10526 to 11664-2.
ISO 11664-2:2007 specifies two illuminants for use in colorimetry. The illuminants are the CIE standard illuminant A and the CIE standard illuminant D65.

Farbmetrik - Teil 2: CIE Normlichtarten (ISO 11664-2:2007)

Diese Internationale Norm legt zwei Lichtarten für die Anwendung in der Farbmetrik fest. Die Lichtarten, die in den Abschnitten 4 und 5 dieser Internationalen Norm definiert sind, sind wie folgt:
a)   CIE-Normlichtart A
Diese Lichtart ist gedacht, typische häusliche Beleuchtung mit Wolfram-Glühfaden zu repräsentieren. Ihre Strahlungsfunktion (relative spektrale Energieverteilung) ist die eines Planckschen Strahlers bei einer Temperatur von etwa 2 856 K. Die CIE-Normlichtart A sollte bei allen Anwendungen in der Farbmetrik angewendet werden, die die Verwendung von Glühlampen-Beleuchtung einschließt, sofern nicht spezifische Gründe für die Anwendung einer anderen Lichtart vorliegen.
b)   CIE-Normlichtart D65
Diese Lichtart ist gedacht, durchschnittliches Tageslicht zu repräsentieren, und sie hat eine ähnlichste Farbtemperatur von etwa 6 500 K. CIE-Normlichtart D65 sollte bei allen farbmetrischen Berechnungen angewendet werden, die repräsentatives Tageslicht erfordern, sofern nicht spezifische Gründe für die Anwendung einer anderen Lichtart vorliegen. Es ist bekannt, dass Variationen in der Strahlungsfunktion (der relativen spektralen Energieverteilung) von Tageslicht besonders im Ultraviolettbereich auftreten, als Funktion von Jahreszeit, Tageszeit und geographischer Lage. Die CIE-Normlichtart D65 sollte jedoch angewendet werden, bis zusätzliche Angaben über diese Variationen vorliegen.
Werte für die Strahlungsfunktion der CIE-Normlichtarten A und D65 sind in Tabelle 1 dieser Internationalen Norm angegeben. Die Werte sind in Intervallen von 1 nm für den Bereich von 300 nm bis 830 nm angegeben.
Der Begriff „Lichtart“ bezieht sich auf eine definierte Strahlungsfunktion, nicht zwangsläufig realisierbar oder verfügbar durch eine künstliche Lichtquelle. Die Lichtarten werden angewendet, um die Farbwerte von reflektierten oder transmittierenden Körperfarben unter festgelegten Beleuchtungsbedingungen zu berechnen.

Colorimétrie - Partie 2: Illuminants CIE normalises (ISO 11664-2:2007)

L'ISO 11664-2:2007 comprend l'ISO 10526:2007 et l'ISO 10526:2007/Cor.1:2008. Son contenu technique est identique à celui de l'ISO 10526:2007. L'ISO 10526:2007/Cor.1:2008 modifie le numéro de référence de la norme de 10526 à 11664-2.
L'ISO 11664-2:2007 définit deux illuminants pour leur emploi en colorimétrie: l'illuminant normalisé A de la CIE et l'illuminant normalisé D65 de la CIE.

Kolorimetrija - 2. del: CIE-standardizirani iluminanti (osvetljevala) (ISO 11664-2:2007)

ISO 11664-2:2007 zajema ISO 10526:2007 in ISO 10526:2007/Cor.1:2008. Njegova tehnična vsebina je identična vsebini ISO 10526:2007. ISO 10526:2007/Cor.1:2008 spreminja referenčno številko standarda z 10526 na 11664-2.
ISO 11664-2:2007 določa dve osvetljevali za uporabo v kolorimetriji. Ti dve osvetljevali sta osvetljevalo A po standardu CIE in osvetljevalo D65 po standardu CIE.

General Information

Status
Published
Publication Date
19-Apr-2011
Current Stage
6060 - Definitive text made available (DAV) - Publishing
Due Date
20-Apr-2011
Completion Date
20-Apr-2011

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SLOVENSKI STANDARD
SIST EN ISO 11664-2:2011
01-julij-2011

Kolorimetrija - 2. del: CIE-standardizirani iluminanti (osvetljevala) (ISO 11664-

2:2007)
Colorimetry - Part 2: CIE standard illuminants (ISO 11664-2:2007)
Farbmetrik - Teil 2: CIE Normlichtarten (ISO 11664-2:2007)
Colorimétrie - Partie 2: Illuminants CIE normalises (ISO 11664-2:2007)
Ta slovenski standard je istoveten z: EN ISO 11664-2:2011
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
SIST EN ISO 11664-2:2011 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 11664-2:2011
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SIST EN ISO 11664-2:2011
EUROPEAN STANDARD
EN ISO 11664-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2011
ICS 17.180.20
English Version
Colorimetry - Part 2: CIE standard illuminants (ISO 11664-
2:2007)

Colorimétrie - Partie 2: Illuminants CIE normalises (ISO Farbmetrik - Teil 2: CIE Normlichtarten (ISO 11664-2:2007)

11664-2:2007)
This European Standard was approved by CEN on 17 March 2011.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European

Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same

status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,

Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 11664-2:2011: E

worldwide for CEN national Members.
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SIST EN ISO 11664-2:2011
EN ISO 11664-2:2011 (E)
Contents Page

Foreword ..............................................................................................................................................................3

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SIST EN ISO 11664-2:2011
EN ISO 11664-2:2011 (E)
Foreword

The text of ISO 11664-2:2007 has been prepared by Technical Committee CIE “International Commission on

Illumination” of the International Organization for Standardization (ISO) and has been taken over as

EN ISO 11664-2:2011 by Technical Committee CEN/TC 139 “Paints and varnishes” the secretariat of which is

held by DIN.

This European Standard shall be given the status of a national standard, either by publication of an identical

text or by endorsement, at the latest by October 2011, and conflicting national standards shall be withdrawn at

the latest by October 2011.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.

According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following

countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech

Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,

Sweden, Switzerland and the United Kingdom.
Endorsement notice

The text of ISO 11664-2:2007 has been approved by CEN as a EN ISO 11664-2:2011 without any

modification.
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SIST EN ISO 11664-2:2011
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SIST EN ISO 11664-2:2011
INTERNATIONAL ISO
STANDARD 11664-2
CIE S 014-2/E
First edition
2007-10-15
Corrected version
2008-11-01
Colorimetry —
Part 2:
CIE standard illuminants
Colorimétrie —
Partie 2: Illuminants CIE normalisés
Reference number
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
ISO 2007
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
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COPYRIGHT PROTECTED DOCUMENT
© ISO 2007

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
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ii © ISO 2007 — All rights reserved
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
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

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

ISO 11664-2 was prepared as Standard CIE S 014-2/E by the International Commission on Illumination, which

has been recognized by the ISO Council as an international standardizing body. It was adopted by ISO under

a special procedure which requires approval by at least 75 % of the member bodes casting a vote, and is

published as a joint ISO/CIE edition.

The International Commission on Illumination (abbreviated as CIE from its French title) is an organization

devoted to international cooperation and exchange of information among its member countries on all matters

relating to the science and art of lighting.

International Standard ISO 11664-2 was prepared by CIE Technical Committee 2-33 Reformulation of CIE

Standard Illuminants A and D65.

ISO 11664-2 was initially published by ISO as ISO 10526:2007, and has subsequently been renumbered to be

part 2 of the ISO 11664 series.
ISO 11664 consists of the following parts, under the general title Colorimetry:

⎯ Part 1: CIE standard colorimetric observers [published previously as ISO 10527:2007, which has been

cancelled]

⎯ Part 2: CIE standard illuminants [published previously as ISO 10526:2007, which has been cancelled]

⎯ Part 4: CIE 1976 L*a*b* Colour space
© ISO 2007 — All rights reserved iii
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SIST EN ISO 11664-2:2011
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
CIE S 014-2/E:2006
Standard
Colorimetry -
Part 2: CIE Standard Illuminants
Colorimétrie - Partie 2: Illuminants normalisés CIE
Farbmessung - Teil 2: CIE Normlichtarten

CIE Standards are copyrighted and shall not be reproduced in any form, entirely or partly,

without the explicit agreement of the CIE.
CIE Central Bureau, Vienna CIE S 014-2/E:2006
Kegelgasse 27, A-1030 Vienna, Austria
UDC: 535.65:006 Descriptor: Standardisation of colour measurement
535.643.2 Standard colorimetric system
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
© CIE, 2006

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced

or utilized in any form or by any means, electronic or mechanical, including photocopying and

microfilm, without permission in writing from CIE Central Bureau at the address below.

CIE Central Bureau
Kegelgasse 27
A-1030 Vienna
Austria
Tel.: +43 1 714 3187 0
Fax: +43 1 714 3187 18
e-mail: ciecb@ping.at
Web: www.cie.co.at/
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
FOREWORD

Standards produced by the Commission Internationale de l’Eclairage (CIE) are a concise

documentation of data defining aspects of light and lighting, for which international harmony

requires such unique definition. CIE Standards are therefore a primary source of

internationally accepted and agreed data, which can be taken, essentially unaltered, into

universal standard systems.
This CIE Standard replaces ISO 10526:1999/CIE S005:1998 and was approved by the

CIE Board of Administration and the National Committees of the CIE. It contains only minor

changes from the previous standard, which was prepared by CIE Technical Committee 2-33,

"Reformulation of CIE Standard Illuminants A and D65" *).

The numerical values of the relative spectral distributions of standard illuminants A and

D65 defined by this Standard are the same, within an accuracy of six significant digits, as

those defined in earlier versions of these illuminants.
TABLE OF CONTENTS

FOREWORD ............................................................................................................................vii

1. SCOPE .................................................................................................................................. 1

2. NORMATIVE REFERENCES................................................................................................ 2

3. DEFINITIONS........................................................................................................................ 2

4. CIE STANDARD ILLUMINANT A.......................................................................................... 4

4.1 Definition .......................................................................................................................... 4

4.2 Theoretical basis.............................................................................................................. 4

4.3 Supplementary notes....................................................................................................... 4

5. CIE STANDARD ILLUMINANT D65...................................................................................... 5

5.1 Definition .......................................................................................................................... 5

5.2 Experimental basis........................................................................................................... 5

5.3 Correlated colour temperature......................................................................................... 5

6. CIE SOURCES FOR PRODUCING CIE STANDARD ILLUMINANTS ................................. 5

6.1 CIE source A.................................................................................................................... 5

6.2 Source for CIE standard illuminant D65 .......................................................................... 6

TABLE 1. RELATIVE SPECTRAL POWER DISTRIBUTIONS OF CIE STANDARD

ILLUMINANTS A AND D65 (wavelengths in standard air). .................................................. 7

ANNEX: BIBLIOGRAPHY (INFORMATIVE) ............................................................................. 7

*) Chairman of this TC was K. D. Mielenz (US), members were: J. J. Hsia (US), J. R. Moore

(GB), A. R. Robertson (CA), H. Terstiege (DE) =, J. F. Verrill (GB) =.

This present revision was finalized by an editorial group in CIE Division 2: J. Gardner (AU), T.

Goodman (UK), K. Mielenz (US), J. Moore (UK), Y. Ohno (US), A. Robertson (CA), J.

Schanda (HU).
© CIE, 2006
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved vii
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
COLORIMETRY - PART 2: CIE STANDARD ILLUMINANTS
1. SCOPE

This International Standard specifies two illuminants for use in colorimetry. The illuminants,

which are defined in clauses 4 and 5 of this International Standard, are as follows:

a) CIE standard illuminant A

This is intended to represent typical, domestic, tungsten-filament lighting. Its relative spectral

power distribution is that of a Planckian radiator at a temperature of approximately 2 856 K.

CIE standard illuminant A should be used in all applications of colorimetry involving the use of

incandescent lighting, unless there are specific reasons for using a different illuminant.

b) CIE standard illuminant D65

This is intended to represent average daylight and has a correlated colour temperature of

approximately 6 500 K. CIE standard illuminant D65 should be used in all colorimetric

calculations requiring representative daylight, unless there are specific reasons for using a

different illuminant. Variations in the relative spectral power distribution of daylight are known

to occur, particularly in the ultraviolet spectral region, as a function of season, time of day,

and geographic location. However, CIE standard illuminant D65 should be used pending the

availability of additional information on these variations.

Values for the relative spectral power distribution of CIE standard illuminants A and

D65 are given in Table 1 of this International Standard. Values are given at 1 nm intervals

from 300 nm to 830 nm.

The term "illuminant" refers to a defined spectral power distribution, not necessarily

realizable or provided by an artificial source. Illuminants are used in colorimetry to compute

the tristimulus values of reflected or transmitted object colours under specified conditions of

illumination. The CIE has also defined illuminant C and other illuminants D. These illuminants

are described in Publication CIE 15:2004 but they do not have the status of primary CIE

standards accorded to the CIE standard illuminants A and D65 described in this International

Standard. It is recommended that one of the two CIE standard illuminants defined in this

International Standard be used wherever possible. This will greatly facilitate the comparison

of published results.

It is noted that in the fields of graphic arts and photography extensive use is also made

of CIE illuminant D50.

In most practical applications of colorimetry, it is sufficient to use the values of CIE

standard illuminants A and D65 at less frequent wavelength intervals or in a narrower spectral

region than defined in this Standard. Data and guidelines that facilitate such practice are

provided in Publication CIE 15:2004, together with other recommended procedures for

practical colorimetry.

The term "source" refers to a physical emitter of light, such as a lamp or the sky. In

certain cases, the CIE recommends laboratory sources that approximate the spectral power

distributions of CIE illuminants. In all cases, however, the definition of a CIE recommended

source is secondary to the definition of the corresponding CIE illuminant, because of the

possibility that, from time to time, new developments will lead to improved sources that

represent a particular illuminant more accurately or are more suitable for laboratory use.

Subclause 6.1 of this International Standard describes CIE source A, which is

recommended for laboratory realizations of CIE standard illuminant A. At present, there is no

CIE recommended source representing CIE standard illuminant D65.
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved 1
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
2. NORMATIVE REFERENCES

The following referenced documents are indispensable for the application 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 15:2004. Colorimetry, 3 edition.

CIE 17.4-1987. International Lighting Vocabulary (ILV) - Joint publication IEC/CIE.

ISO 23603:2005/CIE S 012/E:2004. Standard method of assessing the spectral quality of

daylight simulators for visual appraisal and measurement of colour.

CIE S 014-1/E:2006. Colorimetry Part 1: CIE standard colorimetric observers. [ISO 11664-1:2007]

3. DEFINITIONS

For the purposes of this International Standard, the following definitions apply. These

definitions are taken from CIE 17.4-1987, where other relevant terms will also be found.

3.1 chromaticity coordinates (see ILV 845-03-33)
ratio of each of a set of three tristimulus values to their sum

NOTE 1: As the sum of the three chromaticity coordinates equals 1, two of them are sufficient

to define a chromaticity.

NOTE 2: In the CIE 1931 and 1964 standard colorimetric systems, the chromaticity co-

ordinates are represented by the symbols x, y, z and x , y , z .
10 10 10
3.2 chromaticity diagram (see ILV 845-03-35)

plane diagram in which points specified by chromaticity co-ordinates represent the

chromaticities of colour stimuli
3.3 CIE standard illuminants

illuminants A and D65 defined by the CIE in terms of relative spectral power distributions

3.4 CIE sources

artificial sources, specified by the CIE, whose relative spectral power distributions are

approximately the same as those of CIE standard illuminants

3.5 CIE 1976 uniform chromaticity scale diagram; CIE 1976 UCS diagram (see ILV 845-

03-53)

uniform chromaticity scale diagram produced by plotting in rectangular co-ordinates v' against

u', quantities defined by the equations
u' = 4X/(X + 15Y + 3Z) = 4x/(-2x + 12y + 3)
v' = 9Y/(X + 15Y + 3Z) = 9y/(-2x + 12y + 3)
X, Y, Z are the tristimulus values in the CIE 1931 or 1964 standard colorimetric

systems, and x, y are the corresponding chromaticity coordinates of the colour stimulus

considered.
3.6 colour temperature T (see ILV 845-03-49)

temperature of a Planckian radiator whose radiation has the same chromaticity as that of a

given stimulus
This definition is a revision of the definition given in CIE 17.4-1987.
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
3.7 correlated colour temperature T (see CIE 15:2004 Section 9.5)

temperature of a Planckian radiator having the chromaticity nearest the chromaticity associated

with the given spectral distribution on a diagram where the (CIE 1931 standard observer based)

u', 2/3v' coordinates of the Planckian locus and the test stimulus are depicted

NOTE 1: The concept of correlated colour temperature should not be used if the chromaticity

2 4 2 1/2 -2

of the test source differs more than ∆C = [(u' -u' ) + ⋅(v' -v' ) ] = 5x10 from the

t P t P

Planckian radiator, where u' ,v' refer to the test source, u' ,v' to the Planckian

t t P P
radiator.

NOTE 2: Correlated colour temperature can be calculated by a simple minimum search

computer program that searches for that Planckian temperature that provides the
smallest chromaticity difference between the test chromaticity and the Planckian
locus or by any other equivalent method.
3.8 daylight illuminant (see ILV 845-03-11)

illuminant having the same, or nearly the same, relative spectral power distribution as a

phase of daylight
3.9 illuminant (see ILV 845-03-10)

radiation with a relative spectral power distribution defined over the wavelength range that

influences object colour perception
3.10 Planckian radiator; blackbody (see ILV 845-04-04)

ideal thermal radiator that absorbs completely all incident radiation, whatever the wavelength,

the direction of incidence or the polarization. This radiator has, for any wavelength and any

direction, the maximum spectral concentration of radiance for a thermal radiator in thermal

equilibrium at a given temperature.
3.11 Planckian locus (see ILV 845-03-41)

locus of points in a chromaticity diagram that represents chromaticities of the radiation of

Planckian radiators at different temperatures
3.12 primary light source (see ILV 845-07-01)
surface or object emitting light produced by a transformation of energy
3.13 secondary light source (see ILV 845-07-02)

surface or object which is not self-emitting but receives light and re-directs it, at least in part,

by reflection or transmission
3.14 tristimulus values (of a colour stimulus) (see ILV 845-03-22)

amounts of the three reference colour stimuli, in a given trichromatic system, required to

match the colour of the stimulus considered

NOTE: In the CIE standard colorimetric systems, the tristimulus values are represented by

the symbols X, Y, Z and X , Y , Z .
10 10 10
This definition is a revision of the definition given in CIE 17.4-1987.

In calculating the chromaticity coordinates of the Planckian radiator the c value according to

ITS-90 has to be used (c = 1,4388) in Planck’s equation for standard air, but assuming n=1.

CIE 15:2004 suggests one possible method recommended by Robertson (1968).
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved 3
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SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006
4. CIE STANDARD ILLUMINANT A
4.1 Definition
The relative spectral power distribution S (λ) is defined by the equation
1 ,435 ×10
exp −1
560 2 848×560
⎛ ⎞
S (λ)= 100⎜ ⎟ × (1)
1,435×10
⎝ ⎠
exp −1
2 848λ

where λ is the wavelength in nanometres and the numerical values in the two exponential

terms are definitive constants originating from the first definition of Illuminant A in 1931.

This spectral power distribution is normalized to the value 100 (exactly) at the
wavelength 560 nm (exactly).
CIE standard illuminant A is defined over the 300 nm to 830 nm spectral region.

NOTE 1: Table 1 provides the relative spectral power distribution of CIE standard illuminant A

between 300 nm and 830 nm to six significant digits, at one nm intervals. For all

practical purposes it suffices to use these tabulated values instead of the values

calculated from equation 1.

NOTE 2: Despite the fact that equation 1 is based on Planck's equation for vacuum, the

wavelengths are to be taken as being in standard air (dry air at 15ºC and
101325 Pa, containing 0,03% by volume of carbon dioxide). This makes CIE

standard illuminant A compatible with other CIE colorimetric and photometric data.

4.2 Theoretical basis
Equation 1 is equivalent to and can be derived from the expression
S(λ) = 100 M (λ,T) / M (560, T), (2)
e,λ e,λ
where
-5 -1
M (λ,T) = c λ [exp(c /λT)- 1] , (3)
e,λ 1 2
λ is the wavelength (in nanometres), and the ratio c /T is given by
c /T = 1,435 x 10 / 2 848 nm. (4)
Since the numerical value of c cancels out of equation 2, this definition of CIE

standard illuminant A involves no assumptions about the numerical values of c , c , and T

1 2
other than the ratio defined in equation 4.
4.3 Supplementary notes

CIE standard illuminant A was originally defined in 1931 (CIE, 1931) as the relative spectral

power distribution of a Planckian radiator of temperature
T = 2 848 K, (5)
CIE 1931
the value of the second radiation constant c then being taken as
c = 14 350 µm⋅K. (6)
2, CIE 1931

This form of definition as given in equation 1 was carefully chosen to ensure that CIE

standard illuminant A was defined as a relative spectral power distribution and not as a

function of temperature. As explained in 4.2 above, the definition of the relative spectral

power distribution has not changed since 1931 and equation 1 simply expresses it in a

general form.

What has changed is the temperature assigned to this distribution. The value of c given

in equation 6 and used by the CIE in 1931 is different from the respective values,

c = 14 320 µm⋅K, c = 14 380 µm⋅K, and c = c = 14 388 µm⋅K, that were
2, ITS-27 2,IPTS-48 2,IPTS-68 2,ITS-90

assigned to this constant in the International Temperature Scales of 1927, 1948, 1968 and

© CIE 2006 — All rights reserved
4 © ISO 2007 — All rights reserved
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SIST EN ISO 11664-2:2011
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CIE S 014-2/E:2006

1990. Although this has had no effect on the relative spectral power distribution of CIE standard

illuminant A, the correlated colour temperatures of sources recommended for laboratory

realizations have been different, over the years, depending on the values of c used.

As may be seen from equation 4, the colour temperatures associated with CIE

standard illuminant A on the various international temperature scales referred to above were

T = 2 842 K, T = 2 854 K, and T = T = 2 856 K, respectively (see 6.1).
27 48 68 90
5. CIE STANDARD ILLUMINANT D65
5.1 Definition

The relative spectral power distribution S (λ) of CIE standard illuminant D65 is defined by

D65

the values given in Table 1 which are presented at 1 nm intervals over the wavelength range

from 300 nm to 830 nm; the wavelength values given apply in standard air. If required, other

intermediate values may be derived by linear interpolation from the published values.

5.2 Experimental basis

The relative spectral power distribution of CIE standard illuminant D65 is based on

experimental measurements of daylight in the wavelength range 330 nm to 700 nm, with

extrapolations to 300 nm and 830 nm, as reported by Judd, MacAdam, and Wyszecki (Judd

et al., 1964). The extrapolated values are believed to be sufficiently accurate for conventional

colorimetric purposes, but are not recommended for non-colorimetric use.
5.3 Correlated colour temperature

CIE standard illuminant D65 has a nominal correlated colour temperature of 6 500 K. The

exact value depends on the convention used to assign a correlated colour temperature to a

stimulus whose chromaticity, as in this case, does not fall precisely on the Planckian locus.

NOTE: Using the value of c = 14 388 µm⋅K specified in the International Temperature

Scale of 1990 and the definition given in 3.7 that lines of constant correlated colour

temperature are normal to the Planckian locus in a chromaticity diagram in which

2v'/3 is plotted against u', where u', v' are the co-ordinates used in the CIE 1976

uniform chromaticity scale diagram, the correlated colour temperature of CIE

standard illuminant D65 is found to be 6 503 K if it is computed according to the

definition in 3.7 using the data of Table 1. This difference from the nominal

temperature of the CIE standard illuminant was judged to be insignificantly small.

6. CIE SOURCES FOR PRODUCING CIE STANDARD ILLUMINANTS
6.1 CIE source A

CIE standard illuminant A can be realized by CIE source A, defined as a gas-filled, tungsten-

filament lamp operating at a correlated colour temperature
2848c
T= K (7)
14350

on a radiation temperature scale specified by a given value of the second radiation constant

c in µm·K. A lamp with a fused-quartz envelope or window is recommended if the spectral

power distribution of the ultraviolet radiation of CIE standard illuminant A is to be realized

more accurately.
Information on the procedure used to derive D65 values is given in CIE 15:2004.
© CIE 2006 — All rights reserved
© ISO 2007 — All rights reserved 5
---------------------- Page: 19 ----------------------
SIST EN ISO 11664-2:2011
ISO 11664-2:2007(E)
CIE S 014-2/E:2006

The value of c specified in the International Temperature Scale of 1990 (ITS-90) is

c = 14 388 µm⋅K, and thus the correlated colour temperature of CIE source A on this

2,ITS-90
scale is given by
1438
...

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