ISO/CIE 23603:2024

International
Standard
ISO/CIE 23603
First edition
Standard method of assessing
2024-10
the spectral quality of daylight
simulators for visual appraisal and
measurement of colour
Méthode normalisée d'évaluation de la qualité spectrale des
simulateurs de lumière du jour pour le jugement visuel et la
mesure des couleurs
Reference number
© ISO/CIE 2024
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© ISO/CIE 2024 – All rights reserved
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 4
4.1 Chromaticity tolerance .4
4.2 Quality grade .4
5 Test methods . 4
5.1 Spectroradiometry .4
5.2 Computations .5
5.2.1 Normalization .5
5.2.2 Chromaticity deviation .5
5.2.3 Virtual metameric pairs .5
5.2.4 Computing metamerism indices .5
6 Tables . 7
Bibliography . 19

© ISO/CIE 2024 – All rights reserved
iii
Foreword
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This document was prepared by the International Commission on Illumination (CIE) in cooperation with
Technical Committee ISO/TC 274, Light and lighting.
This first edition of ISO/CIE 23603 cancels and replaces ISO 23603:2005, which has been technically revised.
The main changes are as follows:
— prior reference numbers of the document (CIE S 012:2004, ISO 23603:2005) replaced by ISO/CIE 23603;
— normative references updated;
— terms and definitions updated;
— minor editorial changes.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

© ISO/CIE 2024 – All rights reserved
iv
Introduction
The purpose of the assessment method described in this document is to quantify the suitability of the
spectral irradiance distribution of a practical daylight simulator of CIE daylight illuminant D55, D75 or
CIE standard daylight illuminants D50 and D65 for the visual appraisal and measurement of colours of
fluorescent or non-fluorescent specimens.
The basis for the assessment is the special metamerism index for change in illuminant, using pairs of virtual
(rather than real) specimens specified by their reflecting and fluorescing properties. The pairs of specimens
are metameric matches under the CIE daylight illuminant, when evaluated with the CIE 1964 standard
colorimetric observer. The method described in this document quantifies the mismatch when the pairs of
virtual specimens are illuminated by the daylight simulator under test and evaluated by the same standard
colorimetric observer.
A visible range metamerism index is derived to quantify the suitability of the simulator for the visible
wavelength range.
An ultraviolet range metamerism index is derived using a different set of virtual metameric pairs, each pair
having a fluorescent and a non-fluorescent specimen which spectrally match for the CIE daylight illuminant
and CIE standard colorimetric observer. The non-fluorescent specimen in each pair is specified by its spectral
radiance factor. The fluorescent specimen in each pair is specified by its spectral reflected radiance factor,
relative spectral distribution of radiance due to fluorescence and spectral external radiant efficiency of the
fluorescent specimen. The ultraviolet range metamerism index quantifies the mismatch due to fluorescence
that results from the use of the daylight simulator and the CIE 1964 standard colorimetric observer.

© ISO/CIE 2024 – All rights reserved
v
International Standard ISO/CIE 23603:2024(en)
Standard method of assessing the spectral quality of daylight
simulators for visual appraisal and measurement of colour
1 Scope
This document specifies a method of assessing the spectral quality of the irradiance provided by a daylight
simulator to be used for visual appraisal of colours or for colour measurements and a method of assigning
a quality grade to the simulator. It specifies the maximum permissible deviation of the chromaticity of the
simulator from the chromaticity of the CIE standard daylight illuminant or CIE daylight illuminant being
simulated for a daylight simulator to be graded by this method.
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.
ISO/CIE 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers
ISO/CIE 11664-2, Colorimetry — Part 2: CIE standard illuminants
ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space
ISO/CIE 11664-5, Colorimetry — Part 5: CIE 1976 L*u*v* Colour Space and u′, v′ Uniform Chromaticity Scale Diagram
CIE 051.2-1999, A Method for Assessing the Quality of Daylight Simulators for Colorimetry
CIE 250:2022, Spectroradiometric measurement of optical radiation sources
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 https:// cie .co .at/ e -ilv
3.1
daylight simulator
device for the visual appraisal or measurement of the colour of materials or surfaces that provides spectral
irradiance approximating a CIE standard illuminant representing a phase of daylight
[SOURCE: CIE S 017:2020, Entry 17-23-025]

© ISO/CIE 2024 – All rights reserved
3.2
quality grade
class of quality of simulation of the spectral irradiance of a CIE illuminant by a
simulator, expressed as a letter symbol A, B, C, D or E, with class A representing the highest quality
[SOURCE: CIE S 017:2020, Entry 17-23-024]
3.3
reflectance factor
R
quotient of the flux reflected in the directions delimited by a given cone with apex at a surface element,
Φ , and the flux reflected in the same directions by a perfect reflecting diffuser identically irradiated or
n
illuminated, Φ
d
Φ
n
R=
Φ
d
Note 1 to entry: The definition holds for a surface element, for the part of the reflected radiation contained in a given
cone with apex at the surface element, and for incident radiation of given spectral composition, polarization and
geometric distribution.
Note 2 to entry: The reflectance factor is also defined spectrally and is called spectral reflectance factor, R(λ).
Note 3 to entry: The ideal isotropic (Lambertian) diffuser with reflectance or transmittance equal to 1 is called a
perfect diffuser.
Note 4 to entry: For regularly reflecting surfaces that are irradiated or illuminated by a beam of small solid angle, the
reflectance factor can be much larger than 1 if the cone includes the mirror image of the source.
Note 5 to entry: If the solid angle of the cone approaches 2π sr, the reflectance factor approaches the reflectance for
the same conditions of irradiation.
Note 6 to entry: If the solid angle of the cone approaches 0 sr, the reflectance factor approaches the radiance factor or
luminance factor for the same conditions of irradiation.
Note 7 to entry: The reflectance factor has unit one.
[SOURCE: CIE S 017:2020, Entry 17-24-070, modified — Notes 8 and 9 to entry omitted.]
3.4
radiance factor
β
e
quotient of the radiance of a surface element in a specified direction, L and the radiance of the perfect
e,n
reflecting diffuser or perfect transmitting diffuser identically irradiated and viewed, L
e,d
L
e,n
β =
e
L
e,d
Note 1 to entry: The definition holds for a surface element of a non-self-radiating medium, in a specified direction and
under specified conditions of irradiation.
Note 2 to entry: Radiance factor is equivalent to reflectance factor or luminance factor when the cone angle is infinitely
small, and is equivalent to reflectance when the cone angle is 2π sr. These quantities are also defined spectrally and
called spectral radiance factor, β(λ), and spectral reflectance factor, R(λ).
Note 3 to entry: The ideal isotropic (Lambertian) diffuser with reflectance or transmittance equal to 1 is called a
perfect diffuser.
Note 4 to entry: For photoluminescent media, the radiance factor contains two components, the reflected radiance
factor, β , and the luminescent radiance factor, β The sum of reflected radiance factor and luminescent radiance
R L.
factor is the total radiance factor, β : β = β + β .
T T R L
© ISO/CIE 2024 – All rights reserved
The subscript R is used here for the reflected radiance factor because it is more intuitive than the traditional S and
avoids confusion with the use of S to denote a state of polarization.
Note 5 to entry: The radiance factor has unit one.
[SOURCE: CIE S 017:2020, Entry 17-24-075, modified — symbol β deleted; Notes 6 and 7 to entry omitted.]
3.5
reflected radiance factor
β
R
quotient of the reflected radiance at a point on a surface of a non-self-radiating medium in a given direction
and that of the perfect reflecting diffuser identically irradiated and viewed
Note 1 to entry: In general, the reflected radiance factor from a surface does not depend upon the relative spectral
distribution of the irradiation. This is not the case for a photoluminescent surface, where it is necessary to specify this
quantity.
Note 2 to entry: The reflected radiance factor has unit one.
[SOURCE: CIE S 017:2020, Entry 17-21-104, modified — Note 3 to entry omitted.]
3.6
fluorescent radiance factor
β
F
irradiation> ratio of the radiance due to fluorescence of the specimen to the radiance of the perfect reflecting
diffuser identically irradiated and viewed
3.7
fluorescent radiant efficiency
quotient of the integrated value of the radiant flux of all wavelengths emitted by fluorescence (fluorescence
band) and the radiant excitation power irradiating the fluorescent material for a given excitation wavelength
Note 1 to entry: The fluorescent radiant efficiency is a measure of the external radiant efficiency of the fluorescent
material; the internal radiant efficiency is obtained by taking a quotient of the emitted radiation and the radiant
excitation power that is absorbed by the fluorescent material.
Note 2 to entry: In this definition the excitation wavelength is considered to be monochromatic. However, in practice,
the excitation radiation will have a wavelength range and distribution.
Note 3 to entry: Fluorescence is understood to include both fluorescent and phosphorescent phenomena with time
constants short enough to be ignored for the application.
Note 4 to entry: The fluorescent radiant efficiency has unit one.
[SOURCE: CIE S 017:2020, Entry 17-24-042]
3.8
spectral external radiant efficiency of the fluorescent specimen
Q(λ’)
quotient of the total radiant flux of all wavelengths emitted by the fluorescent process for an excitation
wavelength and the total radiant excitation (3.9) power irradiating the fluorescent material
Note 1 to entry: This quantity is also measured in relative terms by comparison to the radiant flux reflected from the
perfect reflecting diffuser identically irradiated and viewed for a given excitation wavelength.
Note 2 to entry: Fluorescence is understood to include both fluorescent and phosphorescent phenomena with time
constants short enough to be ignored for the application.
Note 3 to entry: The spectral external radiant efficiency of the fluorescent specimen has unit one.
[SOURCE: CIE S 017:2020, Entry 17-21-088]

© ISO/CIE 2024 – All rights reserved
3.9
total radiant excitation
N
total radiant power irradiating the specimen that is capable of exciting fluorescence
3.10
relative spectral distribution of radiance due to fluorescence
F(λ)
ratio of the spectral distribution of radiance due to fluorescence to the sum of the tabulated values of this
distribution, i.e. Σ F(λ) = 1,0
λ
4 Requirements
4.1 Chromaticity tolerance
The first requirement of a daylight simulator is that the light it provides be nearly the same chromaticity as
the light of the CIE daylight illuminant. For a daylight simulator to qualify for classification by this document,
the CIE 1976 u' v' chromaticity difference in accordance with ISO/CIE 11664-5 between the light of the
10 10
daylight simulator and that of the CIE daylight illuminant shall not exceed 0,015 in accordance with CIE
051.2-1999.
4.2 Quality grade
The chromaticity requirement described in 4.1 having been met, and a metamerism index having been
determined by the method of this document, the spectral quality of simulation shall be classified, using a
letter symbol indicating a quality grade, according to Table 1.
The quality of spectral simulation is evaluated for the visible spectrum and for the ultraviolet spectrum
and separate quality grades are assigned for those two spectral regions. The quality grades are reported as
a two-letter symbol, the quality grade for the visible region being stated first. For example, the symbol BC
means the daylight simulator has a quality grade of B for the visible spectrum and C for the ultraviolet
spectrum. (Daylight simulators having the BC grade have been found useful for many applications.)
5 Test methods
5.1 Spectroradiometry
The relative spectral irradiance (the relative spectral power distribution of the flux incident on the
specimen) of the daylight simulator shall be measured by spectroradiometry for the near ultraviolet and
visible spectrum, in the wavelength range from 300 nm to 780 nm. The radiometric quantity required is the
relative spectral irradiance at the surface to be observed or measured. This procedure takes into account
not only the relative spectral radiance of the source but also the spectral effect of any lenses, reflectors,
diffusers or filters that affect the relative spectral irradiance.
Devices providing significant spectral irradiance at wavelengths less than 300 nm are not suitable as
daylight simulators. Radiant power at wavelengths of less than 300 nm, coming from the sun, is absorbed in
the earth’s atmosphere, and is insignificant at ground level in natural daylight.
The relative spectral irradiance shall be measured at 5 nm intervals and over 5 nm bands, at wavelengths
from 300 nm to 780 nm. This may be accomplished by direct measurement or a combination of measurement
and interpolation, depending on the nature of the spectroradiometer and whether the relative spectral
irradiance includes some component of a line spectrum. When the spectral power distribution of the daylight
simulator includes spectral lines, as is the case when fluorescent lamps are used, the spectral data shall be
treated by the method in CIE 250:2022.

© ISO/CIE 2024 – All rights reserved
5.2 Computations
5.2.1 Normalization
The spectral irradiance of the daylight simulator is normalized so the assessment is independent of the
absolute value of irradiance. The normalized irradiance shall be computed by Formula (1):
100⋅S()λ
S λ = (1)
()
n
Syλλ⋅ ⋅Δλ
() ()
∑ 10
where
S(λ) is the measured irradiance, the subscript n denotes the normalized quantity,
is one of the colour-matching functions of the CIE 1964 standard colorimetric observer in
y λ
()
accordance with ISO/CIE 11664-1,
Δλ is the wavelength interval used for the summation, and the summation is over the wave-
length range from 300 nm to 780 nm; Δλ shall be 5 nm.
NOTE Although y λ is not defined below 380 nm, the wavelength range is given as 300 nm to 780 nm in
()
order not to give the impression that only the wavelength range 380 nm to 780 nm is needed.
5.2.2 Chromaticity deviation
The CIE 1976 u' v' chromaticity difference between the light from the daylight simulator and that of the
10 10
simulated CIE standard daylight illuminant in accordance with ISO/CIE 11664-2 or CIE daylight illuminant
shall not exceed 0,015. To facilitate this computation, the chromaticity coordinates of the four respective CIE
daylight illuminants as given in CIE 015:2018 are listed in Table 2.
5.2.3 Virtual metameric pairs
5.2.3.1 Pairs for visible-range assessment
Sets of virtual metameric pairs of specimens for visible-range assessment are specified by their spectral
radiance factors in Tables 3 and 4 to 7. Each pair has a "standard" spectrum and a "comparison" spectrum,
representing virtual specimens that match for the CIE 1964 standard colorimetric observer. The five
standard spectra are listed in Table 3 and the same set of five is used for all four CIE daylight illuminants.
Five comparison spectra are listed for each of the four CIE daylight illuminants in Tables 4 to 7.
5.2.3.2 Pairs for ultraviolet-range assessment
Three virtual metameric pairs of specimens for ultraviolet-range assessment are specified in Tables 8 to 12.
Three virtual fluorescent specimens are listed in Table 8. Their reflection and fluorescence properties are
specified by tabulated values of the spectral reflected radiance factor β (λ), the relative spectral distribution of
R
radiance due to fluorescence F(λ) and the spectral external radiant efficiency of the fluorescent specimen Q(λ').
Three virtual non-fluorescent specimens are listed in Tables 9 to 12. Their reflection properties are specified
by their spectral reflectance factors for each of the CIE daylight illuminants.
5.2.4 Computing metamerism indices
5.2.4.1 General
Tristimulus values shall be computed by integrating the product of the colour-matching functions of the
CIE 1964 standard colorimetric observer, the normalized relative spectral irradiance of the daylight

© ISO/CIE 2024 – All rights reserved
simulator and the tabulated properties of the virtual specimens over the wavelength range and intervals
specified in Tables 4 to 7 (visible-range assessment) and Tables 8 to 12 (ultraviolet-range assessment). (See
also CIE 015:2018.)
5.2.4.2 Indices for visible-range assessment
Using the normalized spectral irradiance of the daylight simulator, tristimulus values shall be computed
for the appropriate five metameric pairs in Tables 3 and 4 to 7. Using the CIE 1976 L*a*b* colour-difference
formula in accordance with ISO/CIE 11664-4, the colour difference between the standard specimen and the
corresponding comparison specimen, ΔE* , shall be computed to at least three decimal places for each of
ab,10
the five pairs. The visible range metamerism index M is the average of the five colour differences. (See also
v
CIE 015:2018.)
5.2.4.3 Indices for ultraviolet-range assessment
The virtual fluorescent specimens absorb radiant power in the ultraviolet region of the spectrum and emit
light in the visible region of the spectrum. The emitted light affects the colour of the specimen. The three
virtual specimens absorb radiant power in three different parts of the ultraviolet spectrum. Their ultraviolet
excitation properties are typical of those in commonly used whitening agents.
When a daylight simulator having both ultraviolet and visible spectral components illuminates a fluorescent
specimen, the specimen reflects some light and emits light due to fluorescence. The light emanating from
the specimen is the sum of these two components. The amount of light emitted due to fluorescence depends
on the fluorescent radiant efficiency of the virtual specimens and the amount of excitation, which depends
on the ultraviolet spectral distribution of irradiance provided by the daylight simulator.
The total radiant excitation, N, of the fluorescent standard specimen in Table 8 is computed by Formula (2):
NS= ()λλ''⋅Q()⋅Δλ' (2)
∑ n
where
S (λ') is the normalized spectral irradiance of the simulator in the spectral region from 300 nm to
n
460 nm,
Q(λ') is the spectral external radiant efficiency of the fluorescent specimen over the same spectral
range, as shown in Table 8, and
Δλ' is the wavelength interval of 5 nm.
The spectral fluorescent radiance factor β (λ) is computed by Formula (3):
F
NF⋅ ()λ
βλ = (3)
()
F
S ()λ
n
where
N is the total radiant excitation computed by Formula (2),
F(λ) is the relative spectral distribution of radiance due to fluorescence as shown in Table 8, and
S (λ) is the normalized spectral irradiance distribution of the simulator.
n
The total spectral radiance factor, β (λ), is computed by Formula (4):
T
βλ()=βλ()+βλ() (4)
TR F
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