standard illuminant

The International Commission on Illumination (usually abbreviated CIE for its French name) is the body responsible for publishing all of the well-known standard illuminants. Each of these is known by a letter or by a letter-number combination.

Illuminants A, B, and C were introduced in 1931, with the intention of respectively representing average incandescent light, direct sunlight, and average daylight. Illuminants D (1967) represent variations of daylight, illuminant E is the equal-energy illuminant, while illuminants F (2004) represent fluorescent lamps of various composition.

There are instructions on how to experimentally produce light sources ("standard sources") corresponding to the older illuminants. For the relatively newer ones (such as series D), experimenters are left to measure to profiles of their sources and compare them to the published spectra:

{{blockquote|At present no artificial source is recommended to realize CIE standard illuminant D65 or any other illuminant D of different CCT. It is hoped that new developments in light sources and filters will eventually offer sufficient basis for a CIE recommendation.|CIE|Technical Report (2004) Colorimetry, 3rd ed., Publication 15:2004, CIE Central Bureau, Vienna}}

Nevertheless, they do provide a measure, called the metamerism index, to assess the quality of daylight simulators.{{cite book|author=CIE Technical Report|year=1999|isbn=978-92-9034-051-5|title=A Method for Assessing the Quality of Daylight Simulators for Colorimetry|url=http://www.cie.co.at/publ/abst/51-2-99.html|series=51.2-1999 (including Supplement 1-1999)|quote=A method is provided for evaluating the suitability of a test source as a simulator of CIE Standard Illuminants D55, D65, or D75. The Supplement, prepared in 1999, adds the CIE Illuminant D50 to the line of illuminants where the method can be applied to. For each of these standard illuminants, spectral radiance factor data are supplied for five pairs of nonfluorescent samples that are metameric matches. The colorimetric differences of the five pairs are computed for the test illuminant; the average of these differences is taken as the visible range metamerism index and is used as a measure of the quality of the test illuminant as a simulator for nonfluorescent samples. For fluorescent samples, the quality is further assessed in terms of an ultraviolet range metamerism index, defined as the average of the colorimetric differences computed with the test illuminant for three further pairs of samples, each pair consisting of a fluorescent and a nonfluorescent sample which are metameric under the standard illuminant.|publisher=Bureau central de la CIE|location=Paris|url-status=dead|archiveurl=https://web.archive.org/web/20080416151749/http://www.cie.co.at/publ/abst/51-2-99.html|archivedate=2008-04-16}}{{cite book|author=CIE Standard|title=Standard Method of Assessing the Spectral Quality of Daylight Simulators for Visual Appraisal and Measurement of Colour|series=S012/E:2004|year=2004|url=http://www.cie.co.at/publ/abst/s012.html}} Prepared by TC 1-53 "A Standard Method for Assessing the Quality of Daylight Simulators". [http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=41694 ISO Standard 23603:2005(E)]. The Metamerism Index tests how well five sets of metameric samples match under the test and reference illuminant. In a manner similar to the color rendering index, the average difference between the metamers is calculated.{{cite journal|title=Evaluation of the quality of different D65 simulators for visual assessment|first=Yuk-Ming|last=Lam|author2=Xin, John H. |date=August 2002|journal=Color Research & Application|volume=27|issue=4|pages=243–251|doi=10.1002/col.10061|hdl=10397/26550|hdl-access=free}}

The CIE defines illuminant A in these terms:

{{blockquote|CIE standard illuminant A 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 2856 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|[https://web.archive.org/web/20171204115107/http://www.cie.co.at:80/publ/abst/s005.html CIE Standard Illuminants for Colorimetry]}}

The spectral radiant exitance of a black body follows Planck's law:

M_{e,\lambda}(\lambda, T) = \frac{c_1 \lambda^{-5}}{\exp\left(\frac{c_2}{\lambda T}\right) - 1}.

At the time of standardizing illuminant A, both $c\_1\; =\; 2\backslash pi\; \backslash cdot\; h\; \backslash cdot\; c^2$ (which does not affect the relative SPD) and $c\_2\; =\; h\; \backslash cdot\; c/k$ were different. In 1968, the estimate of c₂ was revised from 0.01438 m·K to 0.014388 m·K (and before that, it was 0.01435 m·K when illuminant A was standardized). This difference shifted the Planckian locus, changing the color temperature of the illuminant from its nominal 2848 K to 2856 K:

T_\text{new} = T_\text{old} \times \frac{1.4388}{1.435} = 2848\ \text{K} \times 1.002648 = 2855.54\ \text{K}.

In order to avoid further possible changes in the color temperature, the CIE now specifies the SPD directly, based on the original (1931) value of c₂:{{clarify|reason=λ here must be dimensionless; is it the wavelength in nm?|date=May 2025}}

S_\text{A}(\lambda) = 100\left(\frac{560}{\lambda}\right)^5 \frac{\exp \frac{1.435 \times 10^7}{2848 \times 560} - 1}{\exp\frac{1.435 \times 10^7}{2848 \lambda} - 1}.

The coefficients have been selected to achieve a normalized SPD of 100 at {{nowrap|560 nm}}. The tristimulus values are {{nowrap|1=(X, Y, Z) = (109.85, 100.00, 35.58)}}, and the chromaticity coordinates using the standard observer are {{nowrap|1=(x, y) = (0.44758, 0.40745)}}.

{{anchor|Illuminant B}}{{anchor|Illuminant C}}

Illuminants B and C are easily achieved daylight simulations. They modify illuminant A by using liquid filters. B served as a representative of noon sunlight, with a correlated color temperature (CCT) of 4874 K, while C represented average day light with a CCT of 6774 K. Unfortunately, they are poor approximations of any phase of natural daylight, particularly in the short-wave visible and in the ultraviolet spectral ranges. Once more realistic simulations were achievable, illuminants B and C were deprecated in favor of the D series.{{cite book|title=Colorimetry: Understanding the CIE System|first=János|last=Schanda|publisher=Wiley Interscience|year=2007|chapter=3: CIE Colorimetry|isbn=978-0-470-04904-4|pages=37–46}}

{{blockquote|Illuminant C does not have the status of CIE standard illuminants but its relative spectral power distribution, tristimulus values and chromaticity coordinates are given in Table T.1 and Table T.3, as many practical measurement instruments and calculations still use this illuminant.|CIE|Publication 15:2004}} Illuminant B was not so honored in 2004.

The liquid filters, designed by Raymond Davis and Kasson S. Gibson in 1931,{{cite journal|first=Raymond|last=Davis|author2=Gibson, Kasson S. |title=Filters for the reproduction of sunlight and daylight and the determination of color temperature|publisher=National Bureau of Standards|date=January 21, 1931|journal=Precision Measurement and Calibration|volume=10|pages=641–805}} have a relatively high absorbance at the red end of the spectrum, effectively increasing the CCT of the incandescent lamp to daylight levels. This is similar in function to a CTB color gel that photographers and cinematographers use today, albeit much less convenient.

Each filter uses a pair of solutions, comprising specific amounts of distilled water, copper sulfate, mannite, pyridine, sulfuric acid, cobalt, and ammonium sulfate. The solutions are separated by a sheet of uncolored glass. The amounts of the ingredients are carefully chosen so that their combination yields a color temperature conversion filter; that is, the filtered light is still white.

{{anchor|Illuminant D}}File:CIE illuminants D and blackbody small.gif

The D series of illuminants are designed to represent natural daylight and lie along the daylight locus. They are difficult to produce artificially, but are easy to characterize mathematically.

By 1964, several spectral power distributions (SPDs) of daylight had been measured independently by H. W. Budde of the National Research Council of Canada in Ottawa, H. R. Condit and F. Grum of the Eastman Kodak Company in Rochester, New York,{{cite journal

| author = Condit, Harold R.

| author2=Grum, Frank

| date=July 1964

| title = Spectral energy distribution of daylight

| journal = JOSA

| volume = 54

| issue=7

| pages = 937–944

| doi = 10.1364/JOSA.54.000937

| bibcode=1964JOSA...54..937C

}} and S. T. Henderson and D. Hodgkiss of Thorn Electrical Industries in Enfield (north London),{{cite journal

| author = Henderson, Stanley Thomas

| author2=Hodgkiss, D.

| year = 1963

| title = The spectral energy distribution of daylight

| journal = British Journal of Applied Physics

| volume = 14

| issue = 3

| pages = 125–131

| doi=10.1088/0508-3443/14/3/307

| bibcode=1963BJAP...14..125H

}}

{{cite journal

| author = Henderson, Stanley Thomas

| author2=Hodgkiss, D.

| year = 1964

| volume=15

| issue=8

| journal=British Journal of Applied Physics

| title = The spectral energy distribution of daylight

| doi=10.1088/0508-3443/15/8/310

| pages=947–952

| bibcode=1964BJAP...15..947H

}} totaling among them 622 samples. Deane B. Judd, David MacAdam, and Günter Wyszecki analyzed these samples and found that the (x, y) chromaticity coordinates followed a simple, quadratic relation, later known as the daylight locus:{{cite journal| title=Spectral Distribution of Typical Daylight as a Function of Correlated Color Temperature|first=Deane B.|last=Judd|author2=MacAdam, David L. |author3=Wyszecki, Günter |journal=JOSA|date=August 1964|volume=54|issue=8|pages=1031–1040|doi=10.1364/JOSA.54.001031|bibcode=1964JOSA...54.1031J }}

:$y\; =\; 2.870\; x\; -\; 3.000\; x^2\; -\; 0.275.$

Characteristic vector analysis revealed that the SPDs could be satisfactorily approximated by using the mean (S₀) and first two characteristic vectors (S₁ and S₂):{{cite journal|journal=JOSA|first=John L.|last=Simonds|title=Application of Characteristic Vector Analysis to Photographic and Optical Response Data|volume=53|issue=8|pages=968–974|date=August 1963|doi=10.1364/JOSA.53.000968|bibcode=1963JOSA...53..968S }}{{cite journal|title=A review of principal component analysis and its applications to color technology|journal=Color Research & Application|first=Di-Yuan|last=Tzeng|author2=Berns, Roy S. |volume=30|issue=2|pages=84–98|date=April 2005|doi=10.1002/col.20086}}

:$S\_D(\backslash lambda)\; =\; S\_0(\backslash lambda)\; +\; M\_1\; S\_1(\backslash lambda)\; +\; M\_2\; S\_2(\backslash lambda).$

File:CIE illuminants D components.svg

In simpler terms, the SPD of the studied daylight samples can be expressed as the linear combination of three, fixed SPDs. The first vector (S₀) is the mean of all the SPD samples, which is the best reconstituted SPD that can be formed with only a fixed vector. The second vector (S₁) corresponds to yellow–blue variation (along the locus), accounting for changes in the correlated color temperature due to proportion of indirect to direct sunlight. The third vector (S₂) corresponds to pink–green variation (across the locus) caused by the presence of water in the form of vapor and haze.

File:Planckian-locus.png is depicted on the CIE 1960 UCS, along with isotherms (lines of constant correlated color temperature) and representative illuminant coordinates]]

By the time the D-series was formalized by the CIE,{{cite conference|title=Proceedings of the 15th Session, Vienna|author=Commission Internationale de l'Eclairage|year=1964}} a computation of the chromaticity $(x,y)$ for a particular isotherm was included.{{cite journal|last=Kelly|first=Kenneth L.|date=August 1963|title=Lines of Constant Correlated Color Temperature Based on MacAdam's (u,v) Uniform Chromaticity Transformation of the CIE Diagram|journal=JOSA|volume=53|issue=8|pages=999–1002|doi=10.1364/JOSA.53.000999}} Judd et al. then extended the reconstituted SPDs to {{nowrap|300 nm}}–{{nowrap|330 nm}} and {{nowrap|700 nm}}–{{nowrap|830 nm}} by using Moon's spectral absorbance data of the Earth's atmosphere.{{cite journal|title=Proposed standard solar-radiation curves for engineering use| first=Parry|last=Moon|date=November 1940|volume=230|issue=5|pages=583–617|journal=Journal of the Franklin Institute|doi=10.1016/S0016-0032(40)90364-7}} The tabulated SPDs presented by the CIE today are derived by linear interpolation of the {{nowrap|10 nm}} data set down to {{nowrap|5 nm}}.[http://files.cie.co.at/204.xls CIE 1931 and 1964 Standard Colorimetric Observers] from {{nowrap|380 nm}} to {{nowrap|780 nm}} in increments of {{nowrap|5 nm}}. However, there is a proposal to use spline interpolation instead.{{cite journal|title=Re-evaluation of daylight spectral distributions|journal=Color Research & Application| volume=25| issue=4| date=August 2000| pages=250–259| first=Balázs|last=Kránicz|author2=Schanda, János|doi=10.1002/1520-6378(200008)25:4<250::AID-COL5>3.0.CO;2-D|url=http://citeseer.ist.psu.edu/282652.html|quote=Later the S₀(λ), S₁(λ) and S₂(λ) functions have been linearly interpolated at 5 nm steps and for even finer step-size also a linear interpolation has been recommended|citeseerx=10.1.1.42.521}}

Similar studies have been undertaken in other parts of the world, or repeating Judd et al.'s analysis with modern computational methods. In several of these studies, the daylight locus is notably closer to the Planckian locus than in Judd et al.Studies from the 1960s and 1970s include:

• {{cite journal|journal=JOSA|volume=56|issue=4|date=April 1966|title=Spectroradiometric and Colorimetric Characteristics of Daylight in the Southern Hemisphere: Pretoria, South Africa|author1=G. T. Winch |author2=M. C. Boshoff |author3=C. J. Kok |author4=A. G. du Toit |name-list-style=amp |pages=456–464|quote=The derived chromaticities were found to be much closer to the full radiator locus than those previously published, which had been obtained in the northern hemisphere.|doi=10.1364/JOSA.56.000456|bibcode=1966JOSA...56..456W }}
• {{cite journal|title=Spectral Distribution and Color of Tropical Daylight|journal=JOSA|first=S.R.|last=Das|author2=Sastri, V.D.P. |volume=55|issue=3|date=March 1965|pages=319–323|doi=10.1364/JOSA.55.000319|bibcode=1965JOSA...55..319D }}
• {{cite journal|title=Typical Spectral Distributions and Color for Tropical Daylight|journal=JOSA|first=V.D.P.|last=Sastri|author2=Das, S.R. |pages=391–398|volume=58|issue=3|date=March 1968|doi=10.1364/JOSA.58.000391|bibcode=1968JOSA...58..391S }}
• {{cite journal|title=Locus of daylight chromaticities in relation to atmospheric conditions|last=Sastri|first=V.D.P.|volume=9|issue=1|date=January 11, 1976|pages=L1–L3|journal=Journal of Physics D: Applied Physics|doi=10.1088/0022-3727/9/1/001|bibcode=1976JPhD....9L...1S |s2cid=250832186 }}
• {{cite journal|title=Spectral distribution of Australian daylight|last=Dixon|first=E.R.|journal=JOSA|volume=68|issue=4|date=April 1978|pages=437–450|doi=10.1364/JOSA.68.000437|bibcode=1978JOSA...68..437D }}

Analyses using the faster computation of the 1990s and 2000s include:

• {{cite journal|title=Testing Linear Models on Spectral Daylight Measurements|first=Javier|last=Hernández-Andrés|author2=Javier Romero |author3=Antonio García-Beltrán |author4=Juan L. Nieves |journal=Applied Optics|volume=37|issue=6|pages=971–977|date=February 20, 1998|doi=10.1364/AO.37.000971|pmid=18268673|bibcode=1998ApOpt..37..971H }}
• {{cite journal|title=Color and spectral analysis of daylight in southern Europe|volume=18|issue=6|date=June 2001|journal=JOSA A|pages=1325–1335|first=Javier|last=Hernández-Andrés |author2=Javier Romero |author3=Juan L. Nieves |author4=Raymond L. Lee Jr |doi=10.1364/JOSAA.18.001325|pmid=11393625 |bibcode=2001JOSAA..18.1325H |citeseerx=10.1.1.384.70}}
• {{cite conference

|title=Group theoretical investigations of daylight spectra

|author1=Thanh Hai Bui |author2=Reiner Lenz |author3=Tomas Landelius |conference=CGIV (European Conference on Colour Graphics, Imaging and Vision)

|year=2004

|pages=437–442

|accessdate = 2008-05-13

|url=http://staffwww.itn.liu.se/~reile/csp-pages/publications/reprints/cgiv04-grouptheory.pdf}}

The CIE positions D65 as the standard daylight illuminant:

{{blockquote|[D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 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.|ISO 10526:1999/CIE S005/E-1998|CIE Standard Illuminants for Colorimetry{{cite web

|url=http://www.cie.co.at/publ/abst/s005.html

|title=CIE Standard Illuminants for Colorimetry

|author=

|date=1999

|website=www.cie.co.at

|publisher=CIE

|access-date=2018-12-17

|archive-url=https://web.archive.org/web/20171204115107/http://www.cie.co.at/publ/abst/s005.html

|archive-date=2017-12-04

|url-status=dead}}}}

File:Daylight-locus-in-CIE-1960-UCS.png

The relative spectral power distribution (SPD) $S\_D\; (\backslash lambda)$ of a D series illuminant can be derived from its chromaticity coordinates in the CIE 1931 color space, $(x\_D,y\_D)$.The coefficients differ from those in the original paper due to the change in the constants in Planck's law. See [http://www.brucelindbloom.com/index.html?Eqn_DIlluminant.html Lindbloom] for the current version, and Planckian locus for details. First, the chromaticity coordinates must be determined:

:$$

x_D = \begin{cases}

0.244063 + 0.09911 \frac{10^3}{T} + 2.9678 \frac{10^6}{T^2} - 4.6070 \frac{10^9}{T^3} & 4000\ \mathrm{K} \leq T \leq 7000\ \ \mathrm{K} \\

0.237040 + 0.24748 \frac{10^3}{T} + 1.9018 \frac{10^6}{T^2} - 2.0064 \frac{10^9}{T^3} & 7000\ \mathrm{K} < T \leq 25000\ \mathrm{K}

\end{cases}

:$y\_D\; =\; -3.000\; x\_D^2\; +\; 2.870\; x\_D\; -\; 0.275$

where T is the illuminant's CCT. Note that the CCTs of the canonical illuminants, D₅₀, D₅₅, D₆₅, and D₇₅, differ slightly from what their names suggest. For example, D50 has a CCT of 5003 K ("horizon" light), while D65 has a CCT of 6504 K (noon light). This is because the value of the constants in Planck's law have been slightly changed since the definition of these canonical illuminants, whose SPDs are based on the original values in Planck's law. The same discrepancy applies to all illuminants in the D series—D₅₀, D₅₅, D₆₅, D₇₅—and can be "rectified" by multiplying the nominal color temperature by $\backslash frac\{c\_2\}\{1.4380\}$; for example $6500\backslash \; \backslash text\{K\}\; \backslash times\; \backslash frac\{1.438776877\backslash dots\}\{1.4380\}\; =\; 6503.51\backslash \; \backslash text\{K\}$ for D₆₅.

To determine the D-series SPD (S_D) that corresponds to those coordinates, the coefficients M₁ and M₂ of the characteristic vectors S₁ and S₂ are determined:

:$S\_D(\backslash lambda)\; =\; S\_0(\backslash lambda)\; +\; M\_1\; S\_1(\backslash lambda)\; +\; M\_2\; S\_2(\backslash lambda),$

:$M\_1\; =\; (-1.3515\; -\; 1.7703\; x\_D\; +\; 5.9114\; y\_D)/M,$

:$M\_2\; =\; (0.0300\; -\; 31.4424\; x\_D\; +\; 30.0717\; y\_D)/M,$

:$M\; =\; 0.0241\; +\; 0.2562\; x\_D\; -\; 0.7341\; y\_D$

where $S\_0(\backslash lambda),\; S\_1(\backslash lambda),\; S\_2(\backslash lambda)$ are the mean and first two eigenvector SPDs, depicted in figure. The characteristic vectors both have a zero at {{nowrap|560 nm}}, since all the relative SPDs have been normalized about this point. In order to match all significant digits of the published data of the canonical illuminants the values of M₁ and M₂ have to be rounded to three decimal places before calculation of S_D.

Using the standard 2° observer, the CIE 1931 color space chromaticity coordinates of D65 are{{cite book |last=Schanda |first=János |editor-last=Schanda |editor-first=János |title=Colorimetry: understanding the CIE system |publisher=John Wiley & Sons |year=2007 |chapter=3. CIE Colorimetry |at=Appendix A, p. 74 }}

$$\backslash begin\{align\}$$

x &= 0.31272 \\

y &= 0.32903

\end{align}

and the XYZ tristimulus values (normalized to {{math|1=Y = 100}}), are

$$\backslash begin\{alignat\}\{2\}$$

X &={}& 95.047 \\

Y &={}& 100\phantom{.000} \\

Z &={}& 108.883

\end{alignat}

For the supplementary 10° observer,{{citation needed|date=April 2023}}

$$\backslash begin\{align\}$$

x &= 0.31382 \\

y &= 0.33100

\end{align}

and the corresponding XYZ tristimulus values are

$$\backslash begin\{alignat\}\{2\}$$

X &={}& 94.811 \\

Y &={}& 100\phantom{.000} \\

Z &={}& 107.304

\end{alignat}

Since D65 represents white light, its coordinates are also a white point, corresponding to a correlated color temperature of 6504 K. Rec. 709, used in HDTV systems, truncates the CIE 1931 coordinates to x=0.3127, y=0.329.

There are no actual daylight light sources, only simulators. Constructing a practical light source that emulates a D-series illuminant is a difficult problem. The chromaticity can be replicated simply by taking a well known light source and applying filters, such as the Spectralight III, that used filtered incandescent lamps.{{cite journal|title=Development of New CIE Sources for Colorimetry|first=Gunter|last=Wyszecki|date=1970|journal=Die Farbe|volume=19|pages=43–}} However, the SPDs of these sources deviate from the D-series SPD, leading to bad performance on the CIE metamerism index.{{cite book

|author=CIE Technical Report

|year=1999

|isbn=978-92-9034-051-5

|title=A Method for Assessing the Quality of Daylight Simulators for Colorimetry

|url=http://www.cie.co.at/publ/abst/51-2-99.html

|issue=51.2–1999 (including Supplement 1–1999)

|quote=A method is provided for evaluating the suitability of a test source as a simulator of CIE Standard Illuminants D55, D65, or D75. The Supplement, prepared in 1999, adds the CIE Illuminant D50 to the line of illuminants where the method can be applied to. For each of these standard illuminants, spectral radiance factor data are supplied for five pairs of nonfluorescent samples that are metameric matches. The colorimetric differences of the five pairs are computed for the test illuminant; the average of these differences is taken as the visible range metamerism index and is used as a measure of the quality of the test illuminant as a simulator for nonfluorescent samples. For fluorescent samples, the quality is further assessed in terms of an ultraviolet range metamerism index, defined as the average of the colorimetric differences computed with the test illuminant for three further pairs of samples, each pair consisting of a fluorescent and a nonfluorescent sample which are metameric under the standard illuminant.

|publisher=Bureau central de la CIE

|location=Paris

|archive-url=https://web.archive.org/web/20170821085424/http://www.cie.co.at/publ/abst/51-2-99.html

|archive-date=2017-08-21

|url-status=dead}}{{cite journal

| author = Lam, Yuk-Ming

|author2=Xin, John H.

|date=August 2002

| title = Evaluation of the quality of different D65 simulators for visual assessment

| journal = Color Research & Application

| volume = 27

| issue = 4

| pages = 243–251

| doi = 10.1002/col.10061

}} Better sources were achieved in the 2010s with phosphor-coated white LEDs that can easily emulate the A, D, and E illuminants with high CRI.{{cite web |title=CIE Illuminant Technology - Yujileds |url=https://www.yujiintl.com/cie-illuminant-technology/ |website=Yujileds - High CRI LED Leader |language=en |date=5 September 2023}}

File:Planckian-locus-whitepoints-crop.png, and roughly at the CCT of D₅₅.]]

Illuminant E is an equal-energy radiator; it has a constant SPD inside the visible spectrum. It is useful as a theoretical reference; an illuminant that gives equal weight to all wavelengths. It also has equal CIE XYZ tristimulus values, thus its chromaticity coordinates are (x,y)=(1/3,1/3). This is by design; the XYZ color matching functions are normalized such that their integrals over the visible spectrum are the same.

Illuminant E is not a black body, so it does not have a color temperature, but it can be approximated by a D series illuminant with a CCT of 5455 K. (Of the canonical illuminants, D₅₅ is the closest.) Manufacturers sometimes compare light sources against illuminant E to calculate the excitation purity.{{cite web|author=Philips|title=Optical Testing for SuperFlux, SnapLED and LUXEON Emitters|url=http://www.philipslumileds.com/pdfs/AB08.pdf|quote=CIE has defined the color coordinates of several different white Illuminants, but within Lumileds, CIE illuminant E is used for all color calculations}}

CIE Publication 15.2 introduced twelve new illuminants representing several fluorescent lamps and comprising series F,[https://cie.co.at/datatable/relative-spectral-power-distributions-illuminants-representing-typical-fluorescent-lamps-0 Spectral power distribution of Illuminants Series FL] ([https://files.cie.co.at/CIE_illum_FLs_1nm.csv CSV] with [https://files.cie.co.at/CIE_illum_FLs_1nm.csv_metadata.json metadata]), in {{nowrap|5 nm}} increments from {{nowrap|380 nm}} to {{nowrap|780 nm}}. later renamed to series FL from CIE Publication 15:2004 onward.{{cite book|author=CIE Technical Report|year=2004|title=Colorimetry|edition=3rd|series=Publication 15:2004|publisher=CIE Central Bureau, Vienna|isbn=978-3-901906-33-6|url=https://cie.co.at/publications/colorimetry-3rd-edition}} The original 12 standards are distributed to 3 groups:

• Standards FL1–FL6 represent "standard" fluorescent lamps consisting of two semi-broadband emissions of antimony and manganese activations in calcium halophosphate phosphor. FL4 is of particular interest since it was used for calibrating the CIE color rendering index (the CRI formula was chosen such that FL4 would have a CRI of 51).{{citation needed|date=January 2025}}
• Standards FL7–FL9 represent "broadband" (full-spectrum light) fluorescent lamps with multiple phosphors, and higher CRIs.
• Standards FL10–FL12 represent narrow triband illuminants consisting of three "narrowband" emissions (caused by ternary compositions of rare-earth phosphors) in the R,G,B regions of the visible spectrum, which leads to poor CRI.

The members within a group represent different CCTs, such that the phosphor weights can be tuned to achieve the desired CCT. In each of these three groups, CIE states that FL2, FL7, and FL11 "take priority" to be representative of their respective groups.

Image:CIE illuminants F 1 to 6 corrected.svg|FL1–6: Standard

Image:CIE illuminants F 7-9.svg|FL7–9: Broadband

Image:CIE illuminants F 10-12.svg|FL10–12: Narrowband

CIE 15:2004 also introduced fifteen new fluorescent illuminants representing different kinds of fluorescent lamps and comprising subseries FL3. These 15 standards are distributed in 5 groups:

• Standards FL3.1-FL3.3 represent standard halophosphate lamps (similar to FL1-6)
• Standards FL3.4-FL3.6 represent DeLuxe type lamps (similar to FL7-9)
• Standards FL3.7-FL3.11 represent three-band lamps (similar to FL10-12)
• Standards FL3.12-FL3.14 represent multi-band lamps
• Standard FL3.15 represents a D65 simulating fluorescent lamp

File:FL3.1 to FL3.3.png|FL3.1-3.3 : standard

File:FL3.4 to FL3.6.png|FL3.4-3.6 : DeLuxe

File:FL3.7 to FL3.11.png|FL3.7-3.11 : three-band

File:FL3.12 to FL3.14.png|FL3.12-3.14 : multi-band

File:FL3.15.png|FL3.15 : D65 simulator

CIE 15:2004 introduced five new illuminants representing different kinds of high pressure discharge lamps and comprising series HP.:

• Standard HP1 for standard high-pressure sodium lamps
• Standard HP2 for color-enhanced high-pressure sodium lamps
• Standards HP3-HP5 for metal halide lamps.

File:HP1 et HP2.png|HP1 and HP2

File:HP3 to HP5.png|HP3 to HP5

CIE Publication 15:2018 introduces nine new illuminants representing several white LEDs with CCTs ranging from 2700~6600 K. LED-B1 through B5 define standard LED illuminants with phosphor-converted blue light. LED-BH1 defines a blend of phosphor-converted blue and a red LED. LED-RGB1 defines the white light produced by a tricolor LED mix. LED-V1 and V2 define LEDs with phosphor-converted violet light.

File:LED-B1 to B5.png|LED-B1 to B5

File:LED-BH1 et RGB1.png|LED-BH1 and RGB1

File:LED-V1 et V2.png|LED-V1 and V2

CIE publication 184:2009 introduced two new illuminants representing natural indoor light,{{cite book |title=Indoor daylight illuminants |date=2009 |publisher=CIE Central Bureau |location=Vienna |isbn=9783901906749}} which were later included as series ID in CIE 15:2018.{{cite book |title=Colorimetry |date=2018 |publisher=Commission Internationale de l'Eclairage |location=Vienna |isbn=978-3-902842-13-8 |edition=4th}} ID50 and ID65 are equivalent to their outdoor counterparts, D50 and D65, filtered through window glass, thereby removing the ultraviolet contents. The indoor CCTs are about 100K higher (cooler) relative to their outdoor counterparts.

{{main|White point}}

The spectrum of a standard illuminant, like any other profile of light, can be converted into tristimulus values. The set of three tristimulus coordinates of an illuminant is called a white point. If the profile is normalized, then the white point can equivalently be expressed as a pair of chromaticity coordinates.

If an image is recorded in tristimulus coordinates (or in values which can be converted to and from them), then the white point of the illuminant used gives the maximum value of the tristimulus coordinates that will be recorded at any point in the image, in the absence of fluorescence. It is called the white point of the image.

The process of calculating the white point discards a great deal of information about the profile of the illuminant, and so although it is true that for every illuminant the exact white point can be calculated, it is not the case that knowing the white point of an image alone tells you a great deal about the illuminant that was used to record it.

{{Color temperature white points}}

{{reflist|30em}}

• [https://web.archive.org/web/20090731074748/http://www.cie.co.at/publ/abst/datatables15_2004/CIE_sel_colorimetric_tables.xls Selected colorimetric tables in Excel], as published in [https://web.archive.org/web/20080213035758/http://www.cie.co.at/publ/abst/15-2004.html CIE 15:2004]
• Konica Minolta Sensing: [https://www5.konicaminolta.eu/en/measuring-instruments/learning-centre/light-measurement/the-language-of-light.html Light sources & Illuminants]

{{Color space}}

{{Color topics}}

Category:Light

Category:Color