Colorimetry - Part 2: CIE standard illuminants (ISO/CIE 11664-2:2022)

This document defines three CIE standard illuminants for use in colorimetry: CIE standard illuminant
A for the representation of typical tungsten-filament lighting, CIE standard illuminant D65 for the
representation of average daylight having a correlated colour temperature of approximately 6 500 K and
CIE standard illuminant D50 for the representation of daylight with a correlated colour temperature of
approximately 5 000 K. Values of the relative spectral power distribution of the three illuminants are
included in this document.

Farbmetrik - Teil 2: CIE Normlichtarten (ISO/CIE 11664-2:2022)

Dieses Dokument definiert drei CIE Normlichtarten zur Anwendung in der Farbmetrik: CIE Normlichtart A für die Repräsentation einer typischen Beleuchtung mit Wolfram-Glühfaden, CIE Normlichtart D65 für die Repräsentation von durchschnittlichem Tageslicht mit einer korrelierten Farbtemperatur von etwa 6 500 K und CIE Normlichtart D50 für die Repräsentation von Tageslicht mit einer korrelierten Farbtemperatur von etwa 5 000 K. Dieses Dokument enthält Werte für die Strahlungsfunktion der drei Lichtarten.

Colorimétrie - Partie 2: Illuminants CIE normalisés (ISO/CIE 11664-2:2022)

Le présent document définit trois illuminants normalisés de la CIE à utiliser en colorimétrie: l’illuminant normalisé A de la CIE représentatif de l’éclairage à incandescence avec filament de tungstène, l’illuminant normalisé D65 de la CIE représentatif d’une lumière du jour moyenne ayant une température de couleur proximale d’environ 6 500 K, et l’illuminant normalisé D50 de la CIE représentatif d’une lumière du jour ayant une température de couleur proximale d’environ 5 000 K. Des valeurs de la répartition spectrale relative d’énergie des trois illuminants sont incluses dans le présent document.

Kolorimetrija - 2. del: Standardizirana osvetljevala (iluminanti) CIE (ISO/CIE 11664-2:2022)

General Information

Status
Published
Public Enquiry End Date
14-Dec-2021
Publication Date
14-Nov-2022
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
26-Oct-2022
Due Date
31-Dec-2022
Completion Date
15-Nov-2022

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Standards Content (sample)

SLOVENSKI STANDARD
SIST EN ISO/CIE 11664-2:2022
01-december-2022
Nadomešča:
SIST EN ISO 11664-2:2011

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

2:2022)
Colorimetry - Part 2: CIE standard illuminants (ISO/CIE 11664-2:2022)
Farbmetrik - Teil 2: CIE Normlichtarten (ISO/CIE 11664-2:2022)
Colorimétrie - Partie 2: Illuminants CIE normalisés (ISO/CIE 11664-2:2022)
Ta slovenski standard je istoveten z: EN ISO/CIE 11664-2:2022
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
SIST EN ISO/CIE 11664-2:2022 en,fr,de

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

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SIST EN ISO/CIE 11664-2:2022
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SIST EN ISO/CIE 11664-2:2022
EN ISO/CIE 11664-2
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2022
EUROPÄISCHE NORM
ICS 17.180.20 Supersedes EN ISO 11664-2:2011
English Version
Colorimetry - Part 2: CIE standard illuminants (ISO/CIE
11664-2:2022)

Colorimétrie - Partie 2: Illuminants CIE normalisés Farbmetrik - Teil 2: CIE Normlichtarten (ISO/CIE

(ISO/CIE 11664-2:2022) 11664-2:2022)
This European Standard was approved by CEN on 2 August 2022.

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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO/CIE 11664-2:2022 E

worldwide for CEN national Members.
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SIST EN ISO/CIE 11664-2:2022
EN ISO/CIE 11664-2:2022 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO/CIE 11664-2:2022
EN ISO/CIE 11664-2:2022 (E)
European foreword

This document (EN ISO/CIE 11664-2:2022) has been prepared by Technical Committee CIE

"International Commission on Illumination" in collaboration with 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 March 2023, and conflicting national standards shall

be withdrawn at the latest by March 2023.

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

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 11664-2:2011.

Any feedback and questions on this document should be directed to the users’ national standards

body/national committee. A complete listing of these bodies can be found on the CEN website.

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, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the

United Kingdom.
Endorsement notice

The text of ISO/CIE 11664-2:2022 has been approved by CEN as EN ISO/CIE 11664-2:2022 without any

modification.
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SIST EN ISO/CIE 11664-2:2022
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SIST EN ISO/CIE 11664-2:2022
INTERNATIONAL ISO/CIE
STANDARD 11664-2
First edition
2022-08
Colorimetry —
Part 2:
CIE standard illuminants
Colorimétrie —
Partie 2: Illuminants CIE normalisés
Reference number
ISO/CIE 11664-2:2022(E)
© ISO/CIE 2022
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/CIE 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester
ISO copyright office CIE Central Bureau
CP 401 • Ch. de Blandonnet 8 Babenbergerstraße 9/9A • A-1010 Vienna
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11 Phone: +43 1 714 3187
Fax: +41 22 749 09 47
Email: copyright@iso.org Email: ciecb@cie.co.at
Website: www.iso.org Website: www.cie.co.at
Published in Switzerland
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 S c op e ................................................................................................................................................................................................................................. 1

2 Nor m at i ve r ef er enc e s ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 CIE standard illuminant A .......................................................................................................................................................................... 2

4.1 Definition ..................................................................................................................................................................................................... 2

4 . 2 T he or e t ic a l b a s i s .................................................................................................................................................................................. 2

5 CIE standard illuminant D65 ..................................................................................................................................................................3

5.1 D efinition ..................................................................................................................................................................................................... 3

5.2 E xperimental basis ............................................................................................................................................................................. 3

5.3 C orrelated colour temperature ................................................................................................................................................ 3

6 CIE standard illuminant D50 .................................................................................................................................................................. 3

6.1 Definition ..................................................................................................................................................................................................... 3

6.2 C orrelated colour temperature ................................................................................................................................................ 3

7 S ources for realizing CIE standard illuminants ................................................................................................................. 4

7.1 S ource for CIE standard illuminant A ................................................................................................................................ 4

7.2 S ources for CIE standard illuminants D65 and D50 ............................................................................................. 4

Annex A (informative) Table of relative spectral power distribution of CIE standard

illuminant A ............................................................................................................................................................................................................... 5

Annex B (normative) Table of relative spectral power distributions of CIE standard

illuminants D65 and D50 .........................................................................................................................................................................18

Annex C (informative) History of the definition of CIE standard illuminant A ...................................................31

Bibliography .............................................................................................................................................................................................................................32

iii
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(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.

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).

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by the International Commission on Illumination (CIE) in cooperation

with Technical Committee ISO/TC 274, Light and lighting, in collaboration with the European Committee

for Standardization (CEN) Technical Committee CEN/TC 139, Paints and varnishes, in accordance with

the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).

This first edition cancels and replaces ISO 11664-2:2007/CIE S 014-2:2006, which has been technically

revised.
The main changes are as follows:

— CIE illuminant D50 has been included as CIE standard illuminant because of its extensive use in the

fields of graphic, arts and photography.

A list of all parts in the ISO/CIE 11664 series can be found on the CIE and ISO websites.

Any feedback or questions on this document should be directed to the CIE Central Bureau or the user’s

national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
Introduction
The illuminants defined in this document are as follows:
a) CIE standard illuminant A

CIE standard illuminant A is intended to represent typical tungsten-filament lighting. Its relative

spectral power distribution is that of a Planckian radiator at a temperature of approximately 2 855,5 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. CIE standard

illuminant A is used in photometry as primary reference spectrum for the calibration of photometric

devices.
b) CIE standard illuminant D65

CIE standard illuminant D65 is intended to represent average daylight having a correlated colour

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

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

different spectral power distribution. 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 is used pending the availability of

additional information on these variations.
c) CIE standard illuminant D50

CIE standard illuminant D50 is intended to represent daylight with a correlated colour temperature of

approximately 5 000 K. CIE standard illuminant D50 should be used in colorimetric calculations where

the use of such a correlated colour temperature is intended.

Values for the relative spectral power distribution of CIE standard illuminants A, D65 and D50 are given

in this document 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 other illuminants, such as illuminant C, other daylight illuminants, and illuminants for LED and

other electric light sources. These illuminants are described in CIE 015, but they do not have the status

of CIE standard illuminants. It is recommended that one of the three CIE standard illuminants defined

in this document be used wherever possible. This will greatly facilitate the comparison of published

results.

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

A, D65 and D50 at less frequent wavelength intervals or in a narrower spectral region than specified in

this document. Data and guidelines that facilitate such practice are provided in CIE 015, together with

other recommended procedures for practical colorimetry.

The term “source” refers to a physical emitter of light, such as a lamp or the sun. 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.

CIE standard source A, the practical realization of CIE standard illuminant A, is described in this

document. At present, there are no CIE-recommended sources representing CIE standard illuminants

D65 and D50.
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
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SIST EN ISO/CIE 11664-2:2022
INTERNATIONAL STANDARD ISO/CIE 11664-2:2022(E)
Colorimetry —
Part 2:
CIE standard illuminants
1 S cope

This document defines three CIE standard illuminants for use in colorimetry: CIE standard illuminant

A for the representation of typical tungsten-filament lighting, CIE standard illuminant D65 for the

representation of average daylight having a correlated colour temperature of approximately 6 500 K and

CIE standard illuminant D50 for the representation of daylight with a correlated colour temperature of

approximately 5 000 K. Values of the relative spectral power distribution of the three illuminants are

included in this document.
2 Normat ive 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
3 Terms and definitions

For the purposes of this document, the terms and definitions given in CIE S 017 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

CIE maintains a terminology database for use in standardization at the following address:

— CIE e-ILV: available at http:// cie .co .at/ e -ilv
3.1
illuminant

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

object colour perception
[SOURCE: CIE S 017:2020, Entry 17-23-018, modified — Notes to entry omitted.]
3.2
CIE standard illuminant
illuminant standardized by the CIE for the purpose of harmonization
[SOURCE: CIE S 017:2020, Entry 17-23-021, modified — Notes to entry omitted.]
3.3
CIE standard source

artificial source specified by the CIE whose radiation approximates a CIE standard illuminant

[SOURCE: CIE S 017:2020, Entry 17-23-022, modified — Notes to entry omitted.]
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
3.4
daylight illuminant
D illuminant

illuminant having the same or nearly the same relative spectral power distribution of the radiant flux

as a phase of daylight
[SOURCE: CIE S 017:2020, Entry 17-23-020, modified — Notes to entry omitted.]
3.5
standard air
dry air at 15 °C and 101 325 Pa, containing 0,045 % by volume of carbon dioxide
[SOURCE: CIE 018:2019, Clause 3]
4 CIE standard illuminant A
4.1 Definition

The relative spectral power distribution of CIE standard illuminant A, S (λ), is defined by Formula (1)

over the wavelength range 300 nm to 830 nm.
1,435×10
5 exp −1
560
 
2 848×560
S ()λ = 100 × (1)
 
  1,435×10
exp −1
2 8848 λ

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 (see also Annex C).

This spectral power distribution is normalized to the value 100 (exactly) at the wavelength 560 nm

(exactly).

NOTE Table A.1 in Annex A provides the relative spectral power distribution of CIE standard illuminant A to

six significant digits, at 1-nm intervals. For practical purposes it suffices to use these tabulated values instead of

the values calculated from Formula (1).

Despite the fact that Formula (1) is based on Planck's equation for vacuum, the wavelengths are to be

taken as being in standard air (see 3.5). This makes CIE standard illuminant A compatible with other

CIE colorimetric and photometric data.
4.2 Theoretical basis
Formula (1) is equivalent to and can be derived from Formula (2):
MT(,λ )
e,λ
S ()λ =100 (2)
MT(,560 )
e,λ
where
 
 
−5 2
MT(,λλ)e=c xp −1 ;
   
e,λ 1
   
 
λ is the wavelength (in nm);
the quotient c /T is given by 14 350 μm⋅K/2 848 K = (1,435 × 10 /2 848) nm.

Since the numerical value of c cancels out Formula (2), this definition of CIE standard illuminant A

involves no assumptions about the numerical values of c , c and T other than the quotient c /T.

1 2 2
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)

The constant c is calculated from h · c/k and its value is 14 387,768 55 … μm·K, using the values of

the Planck constant, h, the speed of light in vacuum, c, and the Boltzmann constant, k, as specified in

[1]

The International System of Units . Using this value for c , the assigned temperature for CIE standard

illuminant A is 2 855,496 ... K, thus approximately 2 855,5 K.

NOTE More information regarding the historical changes to the temperature used to define CIE standard

illuminant A can be found in Annex C.
5 CIE standard illuminant D65
5.1 Definition

CIE standard illuminant D65 shall be as defined in Annex B by the relative spectral power distribution

values provided in Column 2 of Table B.1. The values 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 shall be derived by linear interpolation from the published values.

5.2 Experimental basi s

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

[2]

and 830 nm, as reported by Judd et al. The extrapolated values are believed to be sufficiently accurate

for conventional colorimetric purposes, but are not recommended for non-colorimetric use.

5.3 C orrelated colour temperature

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

[3]

NOTE Using the value of c = 14 388 μm·K specified in the International Temperature Scale of 1990, the

definition of correlated colour temperature (CIE S 017, 17–23–068) and the relative spectral power distribution

data of Table B.1, the correlated colour temperature of CIE standard illuminant D65 is found to be 6 502,712 K.

Using the value of c = 14 387,768 775 … μm·K, as shown in 4.2, the definition of correlated colour temperature

(CIE S 017, 17–23–068) and the relative spectral power distribution data of Table B.1, the correlated colour

temperature of CIE standard illuminant D65 is found to be 6 502,608 K. The difference from the nominal

correlated colour temperature of 6 500 K of CIE standard illuminant D65 is judged to be insignificantly small.

6 CIE standard illuminant D50
6.1 Definition

CIE standard illuminant D50 shall be as defined in Annex B by the relative spectral power distribution

values provided in Column 3 of Table B.1. The values 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 shall be derived by linear interpolation from the published values.

6.2 C orrelated colour temperature

CIE standard illuminant D50 has a nominal correlated colour temperature of 5 000 K.

[3]

NOTE Using the value of c = 14 388 μm·K specified in the International Temperature Scale of 1990, the

definition of correlated colour temperature (CIE S 017, 17–23–068) and the relative spectral power distribution

data of Table B.1, the correlated colour temperature of CIE standard illuminant D50 is found to be 5 001,319 K.

Using the value of c = 14 387,768 775 … μm·K, as shown in 4.2, the definition of correlated colour temperature

(CIE S 017, 17–23–068) and the relative spectral power distribution data of Table B.1, the correlated colour

temperature of CIE standard illuminant D50 is found to be 5 001,239 K. The difference from the nominal

correlated colour temperature of 5 000 K of CIE standard illuminant D50 is judged to be insignificantly small.

© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)

The actual correlated colour temperature of CIE standard illuminant D50 is slightly different from

5 000 K; however, this is judged to be visually insignificant.
7 S ources for realizing CIE standard illuminants
7.1 S ource for CIE standard illuminant A

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

filament lamp operating at an assigned temperature T = (2 848 K/14 350 μm⋅K) ⋅ c where c is

2, 2

expressed 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.

The assigned temperature, T, is currently approximated to 2 855,5 K as shown in 4.2.

7.2 S ources for CIE standard illuminants D65 and D50

At present, there are no CIE-recommended standard sources for realizing CIE standard illuminants D65

and D50. The quality of sources intended for laboratory realization of CIE standard illuminant D65 or

[4]
D50 can be assessed by a method described in ISO 23603/CIE S 012.
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
Annex A
(informative)
Table of relative spectral power distribution of CIE standard
illuminant A

CIE standard illuminant A is defined by Formula (1) in 4.1. Table A.1 is provided for practical use only.

Table A.1 — Relative spectral power distribution of CIE standard illuminant A (wavelengths in

standard air)
λ/nm S (λ)
300 0,930 483
301 0,967 643
302 1,005 97
303 1,045 49
304 1,086 23
305 1,128 21
306 1,171 47
307 1,216 02
308 1,261 88
309 1,309 10
310 1,357 69
311 1,407 68
312 1,459 10
313 1,511 98
314 1,566 33
315 1,622 19
316 1,679 59
317 1,738 55
318 1,799 10
319 1,861 27
320 1,925 08
321 1,990 57
322 2,057 76
323 2,126 67
324 2,197 34
325 2,269 80
326 2,344 06
327 2,420 17
328 2,498 14
329 2,578 01
330 2,659 81
331 2,743 55
332 2,829 28
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
Table A.1 (continued)
λ/nm S (λ)
333 2,917 01
334 3,006 78
335 3,098 61
336 3,192 53
337 3,288 57
338 3,386 76
339 3,487 12
340 3,589 68
341 3,694 47
342 3,801 52
343 3,910 85
344 4,022 50
345 4,136 48
346 4,252 82
347 4,371 56
348 4,492 72
349 4,616 31
350 4,742 38
351 4,870 95
352 5,002 04
353 5,135 68
354 5,271 89
355 5,410 70
356 5,552 13
357 5,696 22
358 5,842 98
359 5,992 44
360 6,144 62
361 6,299 55
362 6,457 24
363 6,617 74
364 6,781 05
365 6,947 20
366 7,116 21
367 7,288 11
368 7,462 92
369 7,640 66
370 7,821 35
371 8,005 01
372 8,191 67
373 8,381 34
374 8,574 04
375 8,769 80
376 8,968 64
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
Table A.1 (continued)
λ/nm S (λ)
377 9,170 56
378 9,375 61
379 9,583 78
380 9,795 10
381 10,009 6
382 10,227 3
383 10,448 1
384 10,672 2
385 10,899 6
386 11,130 2
387 11,364 0
388 11,601 2
389 11,841 6
390 12,085 3
391 12,332 4
392 12,582 8
393 12,836 6
394 13,093 8
395 13,354 3
396 13,618 2
397 13,885 5
398 14,156 3
399 14,430 4
400 14,708 0
401 14,989 1
402 15,273 6
403 15,561 6
404 15,853 0
405 16,148 0
406 16,446 4
407 16,748 4
408 17,053 8
409 17,362 8
410 17,675 3
411 17,991 3
412 18,310 8
413 18,633 9
414 18,960 5
415 19,290 7
416 19,624 4
417 19,961 7
418 20,302 6
419 20,647 0
420 20,995 0
© ISO/CIE 2022 – All rights reserved
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SIST EN ISO/CIE 11664-2:2022
ISO/CIE 11664-2:2022(E)
Table A.1 (continued)
λ/nm S (λ)
421 21,346 5
422 21,701 6
423 22,060 3
424 22,422 5
425 22,788 3
426 23,157 7
427 23,530 7
428 23,907 2
429 24,287 3
430 24,670 9
431 25,058 1
432 25,448 9
433 25,843 2
434 26,241 1
435 26,642 5
436 27,047 5
437 27,456 0
...

SLOVENSKI STANDARD
oSIST prEN ISO/CIE 11664-2:2021
01-december-2021

Kolorimetrija - 2. del: Standardizirana osvetljevala (iluminanti) CIE (ISO/CIE DIS

11664-2.2:2021))
Colorimetry - Part 2: CIE standard illuminants (ISO/CIE DIS 11664-2.2:2021)
Farbmetrik - Teil 2: CIE Normlichtarten (ISO/CIE DIS 11664-2.2:2021)
Colorimétrie - Partie 2: Illuminants CIE normalisés (ISO/CIE DIS 11664-2.2:2021)
Ta slovenski standard je istoveten z: prEN ISO/CIE 11664-2
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
oSIST prEN ISO/CIE 11664-2:2021 en,fr,de

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

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oSIST prEN ISO/CIE 11664-2:2021
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oSIST prEN ISO/CIE 11664-2:2021
DRAFT INTERNATIONAL STANDARD
ISO/CIE DIS 11664-2.2
CIE Secretariat: CIE
Voting begins on: Voting terminates on:
2021-10-22 2021-12-17
Colorimetry —
Part 2:
CIE standard illuminants
Colorimétrie —
Partie 2: Illuminants CIE normalisés
ICS: 17.180.20
Member bodies are requested to consult relevant national interests in ISO/TC
274 before casting their ballot to the e-Balloting application.
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/CIE DIS 11664-2.2:2021(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO/CIE 2021
---------------------- Page: 3 ----------------------
oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/CIE 2021

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office CIE Central Bureau
CP 401 • Ch. de Blandonnet 8 Babenbergerstraße 9/9A
CH-1214 Vernier, Geneva A-1010 Vienna, Austria
Phone: +41 22 749 01 11 Phone: +43 1 714 3187
Email: copyright@iso.org Email: ciecb@cie.co.at
Website: www.iso.org Website: www.cie.co.at
Published in Switzerland
ii © ISO/CIE 2021 – All rights reserved
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
Contents

Foreword ................................................................................................................................................................iv

Introduction ........................................................................................................................................................... v

1 Scope .......................................................................................................................................................... 1

2 Normative references .......................................................................................................................... 1

3 Terms and definitions .......................................................................................................................... 1

4 CIE standard illuminant A ................................................................................................................... 2

4.1 Definition .................................................................................................................................................. 2

4.2 Theoretical basis .................................................................................................................................... 2

5 CIE standard illuminant D65 ............................................................................................................. 3

5.1 Definition .................................................................................................................................................. 3

5.2 Experimental basis ................................................................................................................................ 3

5.3 Correlated colour temperature ........................................................................................................ 3

6 CIE standard illuminant D50 ............................................................................................................. 4

6.1 Definition .................................................................................................................................................. 4

6.2 Correlated colour temperature ........................................................................................................ 4

7 Sources for realizing CIE standard illuminants .......................................................................... 4

7.1 Source for CIE standard illuminant A ............................................................................................. 4

7.2 Sources for CIE standard illuminants D65 and D50 .................................................................. 4

Annex A (informative) Table of relative spectral power distribution of CIE standard

illuminant A ............................................................................................................................................. 5

Annex B (normative) Table of relative spectral power distributions of CIE standard

illuminants D65 and D50 .................................................................................................................... 9

Annex C (informative) History of CIE standard illuminant A ............................................................ 17

Bibliography ....................................................................................................................................................... 18

© ISO/CIE 2021 – All rights reserved iii
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(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.

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).

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on

the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by the International Commission on Illumination (CIE) in cooperation with

ISO/TC 274 “Light and Lighting”.

This first edition of ISO/CIE 11664-2 cancels and replaces ISO 11664-2:2007/CIE S 014-2:2006, which

has been technically revised.
The main changes compared to the previous edition are as follows:

— CIE illuminant D50 has been included as CIE standard illuminant in this document because of its

extensive use in the fields of graphic, arts and photography.

A list of all parts in the ISO/CIE 11664 series can be found on the ISO website and CIE website.

Any feedback or questions on this document should be directed to the CIE Central Bureau or to the user’s

national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

iv © ISO/CIE 2021 – All rights reserved
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
Introduction
The illuminants defined in this document are as follows:
a) CIE standard illuminant A

CIE standard illuminant A is intended to represent typical tungsten-filament lighting. Its relative spectral

power distribution is that of a Planckian radiator at a temperature of approximately 2 855,5 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. CIE standard illuminant A is

used in photometry as primary reference spectrum for the calibration of photometric devices.

b) CIE standard illuminant D65

CIE standard illuminant D65 is intended to represent average daylight having a correlated colour

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

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

different spectral power distribution. 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 is used pending the availability of additional

information on these variations.
c) CIE standard illuminant D50

CIE standard illuminant D50 is intended to represent daylight with a correlated colour temperature of

approximately 5 000 K. CIE standard illuminant D50 should be used in colorimetric calculations where

the use of such a correlated colour temperature is intended.

Values for the relative spectral power distribution of CIE standard illuminants A, D65 and D50 are given

in this document 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 other illuminants, such as illuminant C, other D illuminants, and illuminants for LED and other

electric light sources. These illuminants are described in Publication CIE 015, but they do not have the

status of CIE standard illuminants. It is recommended that one of the three CIE standard illuminants

defined in this document be used wherever possible. This will greatly facilitate the comparison of

published results.

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

A, D65 and D50 at less frequent wavelength intervals or in a narrower spectral region than defined in this

document. Data and guidelines that facilitate such practice are provided in Publication CIE 015, 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.

CIE standard source A, the practical realization of CIE standard illuminant A, is described in this

document. At present, there are no CIE recommended sources representing CIE standard illuminants D65

and D50.
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oSIST prEN ISO/CIE 11664-2:2021
DRAFT INTERNATIONAL STANDARD ISO/CIE DIS 11664-2.2:2021(E)
Colorimetry — Part 2: CIE standard illuminants
1 Scope

This document defines three CIE standard illuminants for use in colorimetry: CIE standard illuminant A

for the representation of typical tungsten-filament lighting, CIE standard illuminant D65 for the

representation of average daylight having a correlated colour temperature of approximately 6 500 K, and

CIE standard illuminant D50 for the representation of daylight with a correlated colour temperature of

approximately 5 000 K. Values of the relative spectral power distribution of the three illuminants are

included in this document.
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 23603/CIE S 012, Standard method of assessing the spectral quality of daylight simulators for visual

appraisal and measurement of colour

BIPM The International System of Units (SI), 9 edition, published on May 20, 2019

3 Terms and definitions

For the purposes of this document, the terms and definitions given in CIE S 017 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
CIE standard illuminant
illuminant standardized by the CIE for the purpose of harmonization
[SOURCE: CIE S 017:2020, Entry 17-23-021, modified – notes to entry omitted]
3.2
CIE standard source

artificial source specified by the CIE whose radiation approximates a CIE standard illuminant

[SOURCE: CIE S 017:2020, Entry 17-23-022, modified – notes to entry omitted]
© ISO/CIE 2021 – All rights reserved 1
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
3.3
daylight illuminant
D illuminant

illuminant having the same or nearly the same relative spectral power distribution of the radiant flux as

a phase of daylight
[SOURCE: CIE S 017:2020, Entry 17-23-020, modified – notes to entry omitted]
3.4
illuminant

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

object colour perception
[SOURCE: CIE S 017:2020, Entry 17-23-018, modified – notes to entry omitted]
3.5
standard air
dry air at 15 °C and 101 325 Pa, containing 0,045 % by volume of carbon dioxide
Note 1 to entry: This definition is intended for this document only.
4 CIE standard illuminant A
4.1 Definition

The relative spectral power distribution of CIE standard illuminant A, S (λ), is defined by Formula (1)

over the wavelength range 300 nm to 830 nm.
1,435×10
exp −1
560 2848×560
S (λ ) 100 × (1)
A 
1,435×10
exp −1
2848λ

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 (see also Annex C). This

spectral power distribution is normalized to the value 100 (exactly) at the wavelength 560 nm (exactly).

Note 1 Table A.1 provides the relative spectral power distribution of CIE standard illuminant A to six significant

digits, at 1 nm intervals. For practical purposes it suffices to use these tabulated values instead of the values

calculated from Formula (1).

Note 2 Despite the fact that Formula (1) is based on Planck's equation for vacuum, the wavelengths are to be

taken as being in standard air (see 3.5). This makes CIE standard illuminant A compatible with other CIE

colorimetric and photometric data.
4.2 Theoretical basis
Formula (1) is equivalent to and can be derived from the expression
MT(,λ )
e,λ
S (λ )= 100 , (2)
MT(560, )
e,λ
where
2 © ISO/CIE 2021 – All rights reserved
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
c
−5 2
M (λ ,T ) c λ exp−1 , (3)

e,λ 1
λ T

λ is the wavelength (in nm),
and the quotient c /T is given by
c 14 350 μm⋅×K 1,435 10
nm . (4)
T 2 848 K 2 848

Since the numerical value of c cancels out of Formula (2), this definition of CIE standard illuminant A

involves no assumptions about the numerical values of c , c , and T other than the quotient defined in

1 2
Formula (4).

With the value of c as defined in (BIPM, The International System of Units (SI), 9th edition), the assigned

temperature for CIE standard illuminant A is 2 855,496 ... K, thus approximately 2 855,5 K.

Note More information regarding the historical changes to the temperature used to define CIE standard

illuminant A can be found in Annex B.
5 CIE standard illuminant D65
5.1 Definition

CIE standard illuminant D65 is defined by the relative spectral power distribution values provided in

Column 2 of Table B.1. The values 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 shall 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.

NOTE Using the value of c = 14 388 µm·K, specified in the International Temperature Scale of 1990, the definition

of correlated colour temperature (CIE S 017, 17-23-068), and the relative spectral power distribution data of Table

B.1, the correlated colour temperature of CIE standard illuminant D65 is found to be 6 502,712 K. Using the value

of c = 14 387,768 775 … µm·K, specified in the International System of Units (SI), 9th edition (2019), the definition

of correlated colour temperature (CIE S 017, 17-23-068), and the relative spectral power distribution data of Table

B.1, the correlated colour temperature of CIE standard illuminant D65 is found to be 6 502,608 K. The difference

from the nominal correlated colour temperature of 6 500 K of CIE standard illuminant D65 is judged to be

insignificantly small.
© ISO/CIE 2021 – All rights reserved 3
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
6 CIE standard illuminant D50
6.1 Definition

CIE standard illuminant D50 is defined by the relative spectral power distribution values provided in

Column 3 of Table B.1. The values 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 shall be derived by linear interpolation from the published values.
6.2 Correlated colour temperature

CIE standard illuminant D50 has a nominal correlated colour temperature of 5 000 K.

NOTE Using the value of c = 14 388 µm·K, specified in the International Temperature Scale of 1990, the

definition of correlated colour temperature (CIE S 017, 17-23-068), and the relative spectral power

distribution data of Table B.1, the correlated colour temperature of CIE standard illuminant D50 is found

to be 5 001,319 K. Using the value of c = 14 387,768 775 … µm·K, specified in the International System

of Units (SI), 9th edition (2019), the definition of correlated colour temperature (CIE S 017, 17-23-068),

and the relative spectral power distribution data of Table B.1, the correlated colour temperature of CIE

standard illuminant D50 is found to be 5 001,239 K. The difference from the nominal correlated colour

temperature of 5 000 K of CIE standard illuminant D50 is judged to be insignificantly small.

The actual correlated colour temperature of CIE standard illuminant D50 is slightly different from 5 000 K; however,

this is judged to be visually insignificant.
7 Sources for realizing CIE standard illuminants
7.1 Source for CIE standard illuminant A

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

filament lamp operating at an assigned temperature
2 848 K⋅c
T= (7)
14 350 μm⋅K

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.

The value of c is 14 387,768 775 … µm·K and thus the assigned temperature of CIE standard source A is

given by
14 387,768 775 ... μm⋅K
T ×=2 848 K 2 855,496 ... K≈ 2 855,5 K (8)
14 350 μm⋅K
7.2 Sources for CIE standard illuminants D65 and D50

At present, there are no CIE recommended standard sources for realizing CIE standard illuminants D65

and D50. The quality of sources intended for laboratory realization of CIE standard illuminant D65 or

D50 can be assessed by a method described in ISO 23603/CIE S 012.
4 © ISO/CIE 2021 – All rights reserved
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
Annex A
(informative)
Table of relative spectral power distribution of CIE standard illuminant A

CIE standard illuminant A is defined by Formula (1) in 4.1. Table A.1 is provided for practical use only.

Table A.1 – Relative spectral power distribution of CIE standard illuminant A (wavelengths in

standard air)
S (λ) S (λ) S (λ) S (λ)
λ/nm λ/nm λ/nm λ/nm
A A A A
300 0,930 483 334 3,006 78 368 7,462 92 402 15,273 6
301 0,967 643 335 3,098 61 369 7,640 66 403 15,561 6
302 1,005 97 336 3,192 53 370 7,821 35 404 15,853 0
303 1,045 49 337 3,288 57 371 8,005 01 405 16,148 0
304 1,086 23 338 3,386 76 372 8,191 67 406 16,446 4
305 1,128 21 339 3,487 12 373 8,381 34 407 16,748 4
306 1,171 47 340 3,589 68 374 8,574 04 408 17,053 8
307 1,216 02 341 3,694 47 375 8,769 80 409 17,362 8
308 1,261 88 342 3,801 52 376 8,968 64 410 17,675 3
309 1,309 10 343 3,910 85 377 9,170 56 411 17,991 3
310 1,357 69 344 4,022 50 378 9,375 61 412 18,310 8
311 1,407 68 345 4,136 48 379 9,583 78 413 18,633 9
312 1,459 10 346 4,252 82 380 9,795 10 414 18,960 5
313 1,511 98 347 4,371 56 381 10,009 6 415 19,290 7
314 1,566 33 348 4,492 72 382 10,227 3 416 19,624 4
315 1,622 19 349 4,616 31 383 10,448 1 417 19,961 7
316 1,679 59 350 4,742 38 384 10,672 2 418 20,302 6
317 1,738 55 351 4,870 95 385 10,899 6 419 20,647 0
318 1,799 10 352 5,002 04 386 11,130 2 420 20,995 0
319 1,861 27 353 5,135 68 387 11,364 0 421 21,346 5
320 1,925 08 354 5,271 89 388 11,601 2 422 21,701 6
321 1,990 57 355 5,410 70 389 11,841 6 423 22,060 3
322 2,057 76 356 5,552 13 390 12,085 3 424 22,422 5
323 2,126 67 357 5,696 22 391 12,332 4 425 22,788 3
324 2,197 34 358 5,842 98 392 12,582 8 426 23,157 7
325 2,269 80 359 5,992 44 393 12,836 6 427 23,530 7
326 2,344 06 360 6,144 62 394 13,093 8 428 23,907 2
327 2,420 17 361 6,299 55 395 13,354 3 429 24,287 3
328 2,498 14 362 6,457 24 396 13,618 2 430 24,670 9
329 2,578 01 363 6,617 74 397 13,885 5 431 25,058 1
330 2,659 81 364 6,781 05 398 14,156 3 432 25,448 9
331 2,743 55 365 6,947 20 399 14,430 4 433 25,843 2
332 2,829 28 366 7,116 21 400 14,708 0 434 26,241 1
333 2,917 01 367 7,288 11 401 14,989 1 435 26,642 5
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
S (λ) S (λ) S (λ) S (λ)
λ/nm λ/nm λ/nm λ/nm
A A A A
436 27,047 5 480 48,242 3 524 75,127 5 568 105,741
437 27,456 0 481 48,796 3 525 75,790 3 569 106,462
438 27,868 1 482 49,353 3 526 76,455 1 570 107,184
439 28,283 6 483 49,913 2 527 77,121 7 571 107,906
440 28,702 7 484 50,476 0 528 77,790 2 572 108,630
441 29,125 3 485 51,041 8 529 78,460 5 573 109,354
442 29,551 5 486 51,610 4 530 79,132 6 574 110,078
443 29,981 1 487 52,181 8 531 79,806 5 575 110,803
444 30,414 2 488 52,756 1 532 80,482 1 576 111,529
445 30,850 8 489 53,333 2 533 81,159 5 577 112,255
446 31,290 9 490 53,913 2 534 81,838 6 578 112,982
447 31,734 5 491 54,495 8 535 82,519 3 579 113,709
448 32,181 5 492 55,081 3 536 83,201 7 580 114,436
449 32,632 0 493 55,669 4 537 83,885 6 581 115,164
450 33,085 9 494 56,260 3 538 84,571 2 582 115,893
451 33,543 2 495 56,853 9 539 85,258 4 583 116,622
452 34,004 0 496 57,450 1 540 85,947 0 584 117,351
453 34,468 2 497 58,048 9 541 86,637 2 585 118,080
454 34,935 8 498 58,650 4 542 87,328 8 586 118,810
455 35,406 8 499 59,254 5 543 88,021 9 587 119,540
456 35,881 1 500 59,861 1 544 88,716 5 588 120,270
457 36,358 8 501 60,470 3 545 89,412 4 589 121,001
458 36,839 9 502 61,082 0 546 90,109 7 590 121,731
459 37,324 3 503 61,696 2 547 90,808 3 591 122,462
460 37,812 1 504 62,312 8 548 91,508 2 592 123,193
461 38,303 1 505 62,932 0 549 92,209 5 593 123,924
462 38,797 5 506 63,553 5 550 92,912 0 594 124,655
463 39,295 1 507 64,177 5 551 93,615 7 595 125,386
464 39,796 0 508 64,803 8 552 94,320 6 596 126,118
465 40,300 2 509 65,432 5 553 95,026 7 597 126,849
466 40,807 6 510 66,063 5 554 95,733 9 598 127,58
467 41,318 2 511 66,696 8 555 96,442 3 599 128,312
468 41,832 0 512 67,332 4 556 97,151 8 600 129,043
469 42,349 1 513 67,970 2 557 97,862 3 601 129,774
470 42,869 3 514 68,610 2 558 98,573 9 602 130,505
471 43,392 6 515 69,252 5 559 99,286 4 603 131,236
472 43,919 2 516 69,896 9 560 100,000 604 131,966
473 44,448 8 517 70,543 5 561 100,715 605 132,697
474 44,981 6 518 71,192 2 562 101,430 606 133,427
475 45,517 4 519 71,843 0 563 102,146 607 134,157
476 46,056 3 520 72,495 9 564 102,864 608 134,887
477 46,598 3 521 73,150 8 565 103,582 609 135,617
478 47,143 3 522 73,807 7 566 104,301 610 136,346
479 47,691 3 523 74,466 6 567 105,020 611 137,075
6 © ISO/CIE 2021 – All rights reserved
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oSIST prEN ISO/CIE 11664-2:2021
ISO/CIE DIS 11664-2.2:2021(E)
S (λ) S (λ) S (λ) S (λ)
λ/nm λ/nm λ/nm λ/nm
A A A A
612 137,804 656 169,203 700 198,261 744 223,826
613 138,532 657 169,895 701 198,884 745 224,361
614 139,260 658 170,586 702 199,506 746 224,893
615 139,988 659 171,275 703 200,125 747 225,423
616 140,715 660 171,963 704 200,743 748 225,951
617 141,441 661 172,650 705 201,359 749 226,477
618 142,167 662 173,335 706 201,972 750 227,000
619 142,893 663 174,019 707 202,584 751 227,522
620 143,618 664 174,702 708 203,195 752 228,041
621 144,343 665 175,383 709 203,803 753 228,558
622 145,067 666 176,063 710 204,409 754 229,073
623 145,790 667 176,741 711 205,013 755 229,585
624 146,513 668 177,419 712 205,616 756 230,096
625 147,235 669 178,094 713 206,216 757 230,604
626 147,957 670 178,769 714 206,815 758 231,110
627 148,678 671 179,441 715 207,411 759 231,614
628 149,398 672 180,113 716 208,006 760 232,115
629 150,117 673 180,783 717 208,599 761 232,615
630 150,836 674 181,451 718 209,189 762 233,112
631 151,554 675 182,118 719 209,778 763 233,606
632 152,271 676 182,783 720 210,365 764 234,099
633 152,988 677 183,447 721 210,949 765 234,589
634 153,704 678 184,109 722 211,532 766 235,078
635 154,418 679 184,770 723 212,112 767 235,564
636 155,132 680 185,429 724 212,691 768 236,047
637 155,845 681 186,087 725 213,268 769 236,529
638 156,558 682 186,743 726 213,842 770 237,008
639 157,269 683 187,397 727 214,415 771 237,485
640 157,979 684 188,050 728 214,985 772 237,959
641 158,689 685 188,701 729 215,553 773 238,432
642 159,397 686 189,350 730 216,120 774 238,902
643 160,104 687 189,998 731 216,684 775 239,370
644 160,811 688 190,644 732 217,246 776 239,836
645 161,516 689 191,288 733 217,806 777 240,299
646 162,221 690 191,931 734 218,364 778 240,760
647 162,924 691 192,572 735 218,920 779 241,219
...

SLOVENSKI STANDARD
oSIST prEN ISO/CIE 11664-2:2020
01-april-2020

Kolorimetrija - 2. del: Standardizirana osvetljevala (iluminanti) CIE (ISO/CIE DIS

11664-2:2020)
Colorimetry - Part 2: CIE standard illuminants (ISO/CIE DIS 11664-2:2020)
Farbmetrik - Teil 2: CIE Normlichtarten (ISO/CIE DIS 11664-2:2020)
Colorimétrie - Partie 2: Illuminants CIE normalisés (ISO/CIE DIS 11664-2:2020)
Ta slovenski standard je istoveten z: prEN ISO/CIE 11664-2
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
oSIST prEN ISO/CIE 11664-2:2020 en,fr,de

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

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oSIST prEN ISO/CIE 11664-2:2020
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oSIST prEN ISO/CIE 11664-2:2020
DRAFT INTERNATIONAL STANDARD
ISO/CIE DIS 11664-2
CIE Secretariat: CIE
Voting begins on: Voting terminates on:
2020-02-13 2020-05-07
Colorimetry —
Part 2:
CIE standard illuminants
Colorimétrie —
Partie 2: Illuminants CIE normalisés
ICS: 17.180.20
Member bodies are requested to consult relevant national interests in ISO/TC
274 before casting their ballot to the e-Balloting application.
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/CIE DIS 11664-2:2020(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION. ISO/CIE 2020
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oSIST prEN ISO/CIE 11664-2:2020
ISO/CIE DIS 11664-2:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/CIE 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office CIE Central Bureau
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Phone: +41 22 749 01 11 Phone: +43 1 714 3187
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Email: copyright@iso.org Email: ciecb@cie.co.at
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Published in Switzerland
ii © ISO/CIE 2020 – All rights reserved
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oSIST prEN ISO/CIE 11664-2:2020
ISO/CIE DIS 11664-2:2020(E)
Contents

Foreword ......................................................................................................................................................................... iv

Introduction..................................................................................................................................................................... v

1 Scope .................................................................................................................................................................... 1

2 Normative references .................................................................................................................................... 1

3 Terms and definitions.................................................................................................................................... 1

4 CIE standard illuminant A ............................................................................................................................ 4

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

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

4.3 Supplementary notes ..................................................................................................................................... 5

5 CIE standard illuminant D65 ....................................................................................................................... 5

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

5.2 Experimental basis ......................................................................................................................................... 6

5.3 Correlated colour temperature .................................................................................................................. 6

6 CIE standard illuminant D50 ....................................................................................................................... 6

6.1 Definition ............................................................................................................................................................ 6

6.2 Correlated colour temperature .................................................................................................................. 6

7 Sources for realizing CIE standard illuminants .................................................................................... 7

7.1 Source for CIE standard illuminant A ....................................................................................................... 7

7.2 Sources for CIE standard illuminants D65 and D50 ............................................................................ 7

Annex A (normative) Table of relative spectral power distributions of CIE standard

illuminants A, D65 and D50 ......................................................................................................................... 8

Bibliography ................................................................................................................................................................. 15

© ISO/CIE 2020 – All rights reserved iii
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oSIST prEN ISO/CIE 11664-2:2020
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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 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.

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).

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

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any

patent rights identified during the development of the document will be in the Introduction and/or on

the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the World

Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by the International Commission on Illumination (CIE) in cooperation with

ISO/TC 274.

This first edition of ISO/CIE 11664-2 cancels and replaces ISO 11664-2:2007/CIE S 014-2:2006, of which

it constitutes a minor revision, incorporating minor editorial updates.

A list of all parts in the ISO/CIE 11664 series can be found on the ISO website and CIE website.

Any feedback or questions on this document should be directed to the CIE Central Bureau or to the user’s

national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

iv © ISO/CIE 2020 – All rights reserved
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ISO/CIE DIS 11664-2:2020(E)
Introduction
The illuminants defined in this document are as follows:
a) CIE standard illuminant A

CIE standard illuminant A is intended to represent typical 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. CIE standard illuminant A is used in

photometry as primary reference spectrum for the calibration of photometric devices.

b) CIE standard illuminant D65

CIE standard illuminant D65 is intended to represent average daylight having a correlated colour

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

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

different spectral power distribution. 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 is used pending the availability of additional

information on these variations.
c) CIE standard illuminant D50

CIE standard illuminant D50 is intended to represent daylight with a correlated colour temperature of

approximately 5 000 K. CIE standard illuminant D50 should be used in colorimetric calculations where

the use of such a correlated colour temperature is intended.

Values for the relative spectral power distribution of CIE standard illuminants A, D65 and D50 are given

in this document 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 other illuminants, such as illuminant C and other D illuminants. These illuminants are described

in Publication CIE 015, but they do not have the status of CIE standard illuminants. It is recommended

that one of the three CIE standard illuminants defined in this document be used wherever possible. This

will greatly facilitate the comparison of published results.

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

A, D65 and D50 at less frequent wavelength intervals or in a narrower spectral region than defined in this

document. Data and guidelines that facilitate such practice are provided in Publication CIE 015, 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.

For laboratory realizations of CIE standard illuminant A, a CIE standard source, the CIE standard source

A, is described in this document. At present, there are no CIE recommended sources representing CIE

standard illuminants D65 and D50.
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Colorimetry — Part 2: CIE standard illuminants
1 Scope

This document specifies three CIE standard illuminants for use in colorimetry: CIE standard

illuminant A for the representation of typical tungsten-filament lighting, CIE standard illuminant

D65 for the representation of average daylight having a correlated colour temperature of

approximately 6 500 K, and CIE standard illuminant D50 for the representation of daylight with a

correlated colour temperature of approximately 5 000 K. Values of the relative spectral power

distribution of the three illuminants are included in this document.
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 23603/CIE S 012 Standard method of assessing the spectral quality of daylight simulators for

visual appraisal and measurement of colour

BIPM The International System of Units (SI), 9 edition, published on May 20, 2019

3 Terms and definitions

For the purposes of this document, the terms and definitions given in CIE S 017 and the following

apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
chromaticity coordinates, pl

coordinates expressing the ratios of each of a set of three tristimulus values to their sum

Note 1 to entry: As the sum of the three chromaticity coordinates equals 1, two of them are sufficient to

define a chromaticity.

Note 2 to entry: In the CIE 1931 and 1964 standard colorimetric systems, the chromaticity coordinates are

represented by the symbols x, y, z and x , y , z .
10 10 10
Note 3 to entry: The chromaticity coordinates are a quantity of unit one.
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[SOURCE: CIE S 017:– , entry 17-23-053]
3.2
chromaticity diagram

plane diagram in which points specified by chromaticity coordinates represent the chromaticities

of colour stimuli

Note 1 to entry: In the CIE standard colorimetric systems y is normally plotted as ordinate and x as abscissa,

to obtain an x, y chromaticity diagram.
[SOURCE: CIE S 017:– , entry 17-23-054]
3.3
CIE standard illuminant
illuminant standardized by the CIE for the purpose of harmonization
[SOURCE: CIE S 017:– , entry 17-23-021, modified – notes to entry omitted]
3.4
CIE standard source

artificial source specified by the CIE whose radiation approximates a CIE standard illuminant

[SOURCE: CIE S 017:– , entry 17-23-022, modified – notes to entry omitted]
3.5
CIE 1976 uniform chromaticity scale diagram
CIE 1976 UCS diagram

uniform chromaticity scale diagram produced by plotting in rectangular coordinates v against u,

quantities defined by the equations
u = 4 X / (X + 15 Y + 3 Z) = 4 x / (−2 x + 12 y + 3)
v = 9 Y / (X + 15 Y + 3 Z) = 9 y / (−2 x + 12 y + 3)

where 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

Note 1 to entry: The CIE 1976 uniform-chromaticity-scale diagram is a modification of, and supersedes, the

CIE 1960 UCS diagram in which v was plotted against u in rectangular coordinates. The relationships

between the two pairs of coordinates are: u = u; v = 1,5 v.
[SOURCE: CIE S 017:– , entry 17-23-073]
3.6
colour temperature

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

stimulus
Note 1 to entry: The colour temperature is expressed in kelvin (K).
[SOURCE: CIE S 017:– , entry 17-23-067]
Under preparation. Stage at the time of publication: CIE DIS 017:2016
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3.7
correlated colour temperature
CCT

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

with the given spectral distribution on a modified 1976 UCS diagram where u, 2/3v are the

coordinates of the Planckian locus and the test stimulus

Note 1 to entry: The concept of correlated colour temperature should not be used if the chromaticity of the

test source differs more than     from the Planckian radiator, where
ΔC = u −u + v −v =510
( ) ( )
t p t p
uv, refer to the test source, uv, to the Planckian radiator.
tt pp

Note 2 to entry: 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 e.g. by a method recommended by Robertson, A.R.

“Computation of correlated color temperature and distribution temperature”, J. Opt. Soc. Am. 58, 1528-

1535, 1968.

(Note that the values in some of the tables in this reference are not up-to-date).

Note 3 to entry: The correlated colour temperature is expressed in kelvin (K).
[SOURCE: IEC 60050-845:– , Term 17-23-068]
3.8
daylight illuminant
D illuminant

illuminant having the same or nearly the same relative spectral power distribution of the radiant

flux as a phase of daylight
[SOURCE: CIE S 017:– , entry 17-23-020]
3.9
illuminant

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

influences object colour perception
[SOURCE: CIE S 017:– , entry 17-23-018, Note 1 to entry omitted.]
3.10
Planckian radiator
blackbody

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

the direction of incidence or the polarization

Note 1 to entry: A Planckian radiator has, for any wavelength and any direction, the maximum spectral

distribution of radiance for a thermal radiator in thermal equilibrium at a given temperature.

[SOURCE: CIE S 017:– , entry 17-24-004]
Under preparation. Stage at the time of publication: IEC CDV 60050-845:2018.
Under preparation. Stage at the time of publication: CIE DIS 017:2016
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3.11
Planckian locus

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

Planckian radiators at different temperatures
[SOURCE: CIE S 017:– , entry 17-23-059]
3.12
tristimulus values, pl

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

the colour of the stimulus considered

Note 1 to entry: In the CIE standard colorimetric systems, the tristimulus values are represented, for

example, by the symbols R, G, B; X, Y, Z; R10, G10, B10;or X10, Y10, Z10.
[SOURCE: CIE S 017:– , entry 17-23-038]
4 CIE standard illuminant A
4.1 Definition

When CIE standard illuminant A is referred, the relative power distribution values provided in

Table A.1 shall be used. If required, other intermediate values may be derived by linear

interpolation from the published values. The relative spectral power distribution of CIE standard

illuminant A, S (), is defined by the equation
1,43510
exp −1
560 2 848 560
S ()=100 (1)
A 
 1,43510
exp −1
2 848 

where  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 A.1 provides the relative spectral power distribution of CIE standard illuminant A between

300 nm and 830 nm to six significant digits, at 1 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 15 ºC and 101 325 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() = 100 M (,T) / M (560, T), (2)
e, e,
where
Under preparation. Stage at the time of publication: CIE DIS 017:2016
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−5 −1
M (,T) = c  [exp(c / T) − 1] , (3)
e, 1 2
 is the wavelength (in nm),
and the ratio c /T is given by
c /T = 1,435  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 other than the

1 2
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

The 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 that were assigned

to this constant in the International Temperature Scales (ITS) or International Practical

Temperature Scales (IPTS) of 1927 (c = 14 320 µmK), 1948 (c = 14 380 µm·K), 1968

2,ITS-27 2,IPTS-48

and 1990 (c = c = 14 388 µm·K). The revised International System of Units (SI) (BIPM,

2,IPTS-68 2,ITS-90

The International System of Units (SI), 9th edition) has fixed the value of the Planck constant,

which changes the value of c to 1,438 776 877 5..  10 m·K. 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 =

ITS-27

2 842 K, T = 2 854 K, and T = T = 2 856 K, respectively (see also 7.1). The assigned

IPTS-48 IPTS-68 ITS-90

temperature for CIE standard illuminant A is 2855,496 K, thus proximately 2855,5 K.

5 CIE standard illuminant D65
5.1 Definition

When CIE standard illuminant D65 is referred, the relative spectral power distribution values

provided in Table A.1 shall be used. The values 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
Information on the procedure used to derive D65 values is given in CIE 15.
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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 1 Using the value of c = 14 388 m·K, specified in the International Temperature Scale of 1990,

the definition given in 0, and the relative spectral power distribution data of Table A.1, the correlated colour

temperature of CIE standard illuminant D65 is found to be 6 503,616 K . The difference from the nominal

correlated colour temperature of 6 500 K of CIE standard illuminant D65 is judged to be visually

insignificant.

NOTE 2 In the case when, instead of the data represented in Table A.1, a calculation method as

recommended in CIE 015 is chosen, the correct rounding of the constants used in the calculations to

reproduce the tabulated data is important.
6 CIE standard illuminant D50
6.1 Definition

When CIE standard illuminant D50 is referred, the relative power distribution values provided in

Table A.1 shall be used. The values 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.

6.2 Correlated colour temperature

CIE standard illuminant D50 has a nominal correlated colour temperature of 5 000 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 1 Using the value of c = 14 388 m·K specified in the International Temperature Scale of 1990,

the definition given in 0, and the relative spectral power distribution data of Table A.1, the correlated colour

temperature of CIE standard illuminant D50 is found to be 5 002,782 K. The difference from the nominal

correlated colour temperature of 5 000 K of CIE standard illuminant D50 is judged to be visually

insignificant.

NOTE 2 In the case when, instead of the data represented in Table A.1, a calculation method as

recommended in CIE 015 is chosen, the correct rounding of the constants used in the calculations to

reproduce the tabulated data is important.
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ISO/CIE DIS 11664-2:2020(E)
7 Sources for realizing CIE standard illuminants
7.1 Source for CIE standard illuminant A

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

tungsten-filament lamp operating at a correlated colour temperature
2 848 Kc
T = (7)
14 350 μmK

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

m·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.

The value of c is 14 387,768 775 … µm·K and thus the correlated colour temperature of CIE

standard source A is given by
14 387,768 775 ... μmK
TK= 2 848 K= 2 855,496 ...  2 855,5 K (8)
14 350 μmK
Sources related to earlier temperature scales may have to be recalibrated.
7.2 Sources for CIE standard illuminants D65 and D50

At present, there are no CIE recommended standard sources for realizing CIE standard illuminants

D65 and D50. The quality of sources intended for laboratory realization of CIE standard illuminant

D65 or D50 can be assessed b
...

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