ISO 23539:2005

INTERNATIONAL ISO
STANDARD 23539
CIE S 010/E
First edition
2005-08-01
Photometry — The CIE system of
physical photometry
Photométrie — Le système CIE de photométrie physique

Reference number
CIE S 010/E:2004
©
ISO 2005
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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.
ISO 23539 was prepared as Standard CIE S 010/E by the International Commission on Illumination, which
has been recognized by the ISO Council as an international standardizing body. It was adopted by ISO under
a special procedure which requires approval by at least 75 % of the member bodes casting a vote, and is
published as a joint ISO/CIE edition.
The International Commission on Illumination (abbreviated as CIE from its French title) is an organization
devoted to international cooperation and exchange of information among its member countries on all matters
relating to the science and art of lighting.
ISO 23539 was prepared by CIE Technical Committee 2-35 CIE Standard for V(λ) and V′(λ).

CIE S 010/E:2004
CIE S 010/E:2004
Standard
PHOTOMETRY - THE CIE SYSTEM
OF PHYSICAL PHOTOMETRY
Photométrie – Le système CIE de photométrie physique
Photometrie - Das CIE-System der physikalischen Photometrie
CIE Standards are copyrighted and shall not be reproduced in any form, entirely or partly,
without the explicit agreement of the CIE.
CIE Central Bureau, Vienna CIE S 010/E:2004
Kegelgasse 27, A-1030 Vienna, Austria
UDC:635.24 Descriptor: Photometry
© CIE 2004 — All rights reserved
CIE S 010/E:2004
” CIE 2004
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced
or utilized in any form or by any means, electronic or mechanical, including photocopying and
microfilm, without permission in writing from CIE Central Bureau at the address below.
CIE Central Bureau
Kegelgasse 27
A-1030 Vienna
Austria
Tel.: +43 1 714 3187 0
Fax: +43 1 714 3187 18
e-mail: ciecb@ping.at
Web: www.cie.co.at
© CIE 2004 — All rights reserved
vi © ISO 2005 — All rights reserved

CIE S 010/E:2004
FOREWORD
Standards produced by the Commission Internationale de l’Eclairage (CIE) are a concise
documentation of data defining aspects of light and lighting, for which international harmony
requires such unique definition. CIE Standards are therefore a primary source of
internationally accepted and agreed data, which can be taken, essentially unaltered, into
universal standard systems.
*)
This International Standard has been prepared by CIE Technical Committee 2-35 ,
"CIE Standard for V(O) and Vƍ(O)", and was approved by the National Committees of the CIE.
TABLE OF CONTENTS
FOREWORD vii
INTRODUCTION 1
1. SCOPE 1
2. PHOTOMETRIC QUANTITIES 1
2.1 Luminous flux 1
2.2 Other quantities 1
3. PHOTOMETRIC UNITS 2
3.1 Candela 2
3.2 Other units 2
4. PHOTOMETRIC STANDARDS 3
4.1 CIE Standard spectral luminous efficiency functions for photopic and scotopic vision 3
4.2 Maximum luminous efficacies for photopic and scotopic vision 3
4.3 Fundamental equations relating photometric and radiometric quantities 4
4.4 Measurement procedures 4
TABLES 5
Table 1. Definitive values of the spectral luminous efficiency function for photopic vision
V(O) 5
Table 2. Definitive values of the spectral luminous efficiency function for scotopic vision
Vƍ(O) 10
ANNEX A (INFORMATIVE) 14
Vocabulary of related terms 14
ANNEX B (INFORMATIVE) 16
Background to the CIE system of physical photometry 16
B.1 Evolution of the photometric base unit 16
B.2 Spectral response of the human eye 16
B.3 Supplementary remarks 17
ANNEX C (INFORMATIVE) 18
Bibliography 18
” CIE 2004
*)
Chairman of this TC was K. D. Mielenz (US), members were: J. Bastie (FR), J. L. Gardner
(AU), F. Hengstberger (ZA), J. R. Moore (GB), Y. Ohno (US), A. C. Parr (US), A. R.
Robertson (CA), G. Sauter (DE), J. Schanda (HU).
© CIE 2004 — All rights reserved
CIE S 010/E:2004
PHOTOMETRY - THE CIE SYSTEM OF PHYSICAL PHOTOMETRY
INTRODUCTION
The visual brightness of a light source depends not only on the amount of radiation it emits
but also on its spectral composition and on the visual response function of the observer
viewing it. Because human visual response varies at different light levels and from person to
person, precise photometry requires the definition of representative standard observers. The
CIE system of physical photometry specifies procedures for the quantitative evaluation of
optical radiation in terms of the spectral luminous efficiency functions of two such standard
observers. One, V(O), represents photopic vision and the other, Vƍ(O), scotopic vision. Used in
conjunction with the SI photometric base unit, the candela, these functions constitute a
system that enables the values of photometric quantities for all types of luminous source to be
precisely determined, regardless of the spectral composition of the radiation emitted.
1. SCOPE
This international Standard specifies the characteristics of the system of physical photometry
established by the CIE and accepted as the basis for the measurement of light. It defines the
photometric quantities, units and standards that make up the CIE system of physical
photometry and that have been officially accepted by the Comité International des Poids et
Mesures (CIPM). They comprise:
 the definition of photometric quantities and units,
 the definition of CIE standard spectral luminous efficiency functions for photopic and
scotopic vision,
 the definition of a CIE standard photometric observer that conforms to these
functions,
 the definition of maximum luminous efficacies for photopic and scotopic vision.
An informative annex provides a vocabulary of related terms.
2. PHOTOMETRIC QUANTITIES
Photometric quantities are defined in the International Lighting Vocabulary (ILV) (CIE, 1987a).
2.1 Luminous flux
The fundamental physical quantity used in optical radiometry is the radiant flux or radiant
power, ) , measured in watts, which is emitted by a source of radiation, transmitted by a
e
medium of propagation, or received at a surface. The corresponding photometric quantity is:
luminous flux () ) (see ILV 845-01-25)
v
quantity derived from radiant flux ) by evaluating the radiation according to its action upon
e
the CIE standard photometric observer
The procedure for deriving )  from )  is defined in 4.3, below.
v e
2.2 Other quantities
The following are the photometric quantities that correspond to the most important radiometric
quantities defined in the International Lighting Vocabulary.
luminous energy (also known as quantity of light) (Q ) (see ILV 845-01-28)
v
time integral of the luminous flux ) over a given duration 't
v
Q ) dt
v v
³
't
luminous intensity (of a source in a given direction) (I ) (see ILV 845-01-31)
v
quotient of the luminous flux d) leaving the source and propagated in the element of solid
v
angle d: containing the given direction, by the element of solid angle
© CIE 2004 — All rights reserved
CIE S 010/E:2004
d)
v
I 
v
dȍ
luminance (in a given direction, at a given point of a real or imaginary surface) (L ) (see ILV
v
845-01-35)
quantity defined by the formula
d)
v
L
v
dA˜ cosT ˜ dȍ
where d) is the luminous flux transmitted by an elementary beam passing through the given
v
point and propagating in the solid angle d: containing the given direction; dA is the area of a
section of that beam containing the given point; T is the angle between the normal to that
section and the direction of the beam
illuminance (at a point of a surface) (E ) (see ILV 845-01-38)
v
quotient of the luminous flux d) incident on an element of the surface containing the point,
v
by the area dA of that element
d)
v
E
v
dA
luminous exitance (at a point of a surface) (M ) (see ILV 845-01-48)
v
quotient of the luminous flux d) leaving an element of the surface containing the point, by
v
the area dA of that element
d)
v
M
v
dA
3. PHOTOMETRIC UNITS
3.1 Candela
The SI photometric base unit is the candela (cd), the unit of luminous intensity. It was defined
by the Conférence Générale des Poids et Mesures (CGPM) in 1979 (CGPM, 1979), as
follows:
The candela is the luminous intensity, in a given direction, of a source that
emits monochromatic radiation of frequency 540 x 10 hertz and that has a
radiant intensity in that direction of (1/683) watt per steradian.
This definition of the candela applies equally to photopic, scotopic, and mesopic
vision.
3.2 Other units
The SI units of other photometric quantities can be derived from the candela and the SI units
of length (m), solid angle (sr) and time (s). Thus:
Quantity Symbol SI Unit
Luminous flux lm = cd·sr
)
v
Luminous energy Q cd·sr·s
v
-2
Luminance L cd·m
v
-2
Illuminance E lx = cd·sr·m
v
-2
Luminous exitance M cd·sr·m
v
© CIE 2004 — All rights reserved
2 © ISO 2005 — All rights reserved

CIE S 010/E:2004
4. PHOTOMETRIC STANDARDS
4.1 CIE Standard spectral luminous efficiency functions for photopic and scotopic vision
This Standard defines two spectral luminous efficiency functions for photometric
measurements:
- The V(O) function, which applies to photopic vision and should be used for
measurements at luminance levels of at least several candelas per square metre. It is defined
by the numerical values given in Table 1 of this Standard, the wavelength being measured in
standard air (Birch, 1994). For numerical computations, the peak value of the V(O) function
should be evaluated at 555 nm exactly. Linear interpolation should be used exclusively to
evaluate V(O) at wavelengths intermediate to those given in Table 1;
- The Vƍ(O) function, which applies to scotopic vision and should be used for
measurements at luminance levels less than some hundredths of a candela per square
metre. This function is defined by the numerical values in Table 2 of this Standard, the
wavelength O again being measured in standard air. For numerical computations, the peak
value of the Vƍ(O) function should be evaluated at 507 nm exactly. Linear interpolation should
be used exclusively to evaluate Vƍ(O) at wavelengths intermediate to those given in Table 2.
An ideal observer having a relative spectral responsivity curve that conforms to the
V(O) function for photopic vision or the Vƍ(O) function for scotopic vision, and that complies
with the summation law implied in the definition of luminous flux, is known as a CIE standard
photometric observer.
The CIE has not, so far, defined standard spectral luminous efficiency functions for
the mesopic region, intermediate between the ranges of photopic and scotopic vision.
4.2 Maximum luminous efficacies for photopic and scotopic vision
The V(O) and Vƍ(O) functions defined in this Standard supplement the 1979 candela definition
in a manner that, taken together, these definitions constitute a rational system of physical
photometry which
 correlates the radiant power of broadband radiation acting upon the human visual
system with the physiological characteristics of the latter,
 is consistent with visual experience for photopic and scotopic vision,
 establishes precisely defined numerical relationships between radiometric and
photometric quantities.
Based on the following definitions and considerations, these numerical relationships
are defined by equations (1) to (4), below.
luminous efficacy (for monochromatic radiation of wavelength O) K(O) and Kƍ(O)
Quotient of the luminous flux ) by the corresponding radiant flux )
v e
)
1
v
>@
K O K ˜V O lm˜ W (for photopic vision) (1)
m
)
e
)'
1
v
K'O K' ˜V'O > lm˜ W @ (for scotopic vision) (2)
m
)
e
where the maximum values of K(O) and Kƍ(O) are denoted by K and Kƍ so that K =
m m m
K(555 nm) and Kƍ = Kƍ(507 nm). The frequency 540 x 10 Hz corresponds to a wavelength
m
of 555,016 nm in standard air and it follows from the candela definition that K(555,016 nm) =
-1
Kƍ(555,016 nm) = 683 lm·W . Therefore, according to equations 1 and 2,
-1 -1
K = 683 [lm·W ] / V(555,016 nm) = 683,002 lm·W  (3)
m
-1 -1
Kƍ = 683 [lm·W ] / Vƍ(555,016 nm) = 1700,05 lm·W  (4)
m
-1
For all practical photometric applications, K can be taken as equal to 683 lm·W and Kƍ
...