IEC 62679-3-3:2016

IEC 62679-3-3 ®
Edition 1.0 2016-09
INTERNATIONAL
STANDARD
colour
inside
Electronic paper displays –
Part 3-3: Optical measuring methods for displays with integrated lighting units
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 15 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: csc@iec.ch.
IEC 62679-3-3 ®
Edition 1.0 2016-09
INTERNATIONAL
STANDARD
colour
inside
Electronic paper displays –
Part 3-3: Optical measuring methods for displays with integrated lighting units

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.120; 31.260 ISBN 978-2-8322-3616-1

– 2 – IEC 62679-3-3:2016 © IEC 2016
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references. 7
3 Terms, definitions and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 8
4 Standard measuring conditions . 8
4.1 Standard environmental measuring conditions . 8
4.2 Viewing direction coordinate system . 8
4.3 Standard lighting conditions . 9
4.3.1 General comments and remarks on the measurement of electronic
paper displays . 9
4.3.2 Dark room conditions . 9
4.3.3 Standard indoor ambient illumination spectra . 9
4.3.4 Standard illumination geometries . 10
4.4 Adjustment of the EPD . 11
4.5 Standard conditions of measuring equipment . 11
4.6 Working standards and references . 11
4.7 Standard locations of measurement field . 11
4.7.1 Matrix displays . 11
4.7.2 Segment displays . 12
5 Optical measuring methods . 12
5.1 Reflection measurements . 12
5.1.1 General . 12
5.1.2 Measuring conditions . 12
5.1.3 Measuring the hemispherical diffuse reflectance . 13
5.1.4 Measuring the reflectance factor for a directed light source . 15
5.2 Display photometric uniformity in a dark room . 16
5.2.1 Purpose . 16
5.2.2 Measuring equipment . 16
5.2.3 Measurement method . 16
5.2.4 Definitions and evaluations. 17
5.3 Dark room contrast ratio . 17
5.3.1 Purpose . 17
5.3.2 Measuring equipment . 17
5.3.3 Measurement method . 17
5.3.4 Definitions and evaluations. 17
5.4 Contrast ratio under indoor illumination . 18
5.4.1 Purpose . 18
5.4.2 Measurement conditions . 18
5.4.3 Measurement method . 18
5.5 Cross-talk . 19
5.5.1 Purpose . 19
5.5.2 Measuring equipment . 19
5.5.3 Greyscale matrix displays. 19
5.5.4 Black and white (two-level) matrix displays . 21

5.6 Display colour, colour gamut, and colour gamut area . 22
5.6.1 Purpose . 22
5.6.2 Measuring equipment . 22
5.6.3 Measurement method . 22
5.6.4 Display colour gamut . 22
5.6.5 Display colour gamut area . 23
5.7 Display colorimetric uniformity in a dark room . 25
5.7.1 Purpose . 25
5.7.2 Measuring equipment . 25
5.7.3 Measurement method . 25
5.7.4 Definitions and evaluations. 26
5.8 Display colour under indoor illumination . 26
5.8.1 Purpose . 26
5.8.2 Measurement conditions . 26
5.8.3 Measurement method . 27
5.8.4 Definitions and evaluations. 27
5.9 Colour gamut volume under indoor illumination . 28
5.9.1 Purpose . 28
5.9.2 Measurement conditions . 28
5.9.3 Measurement method . 28
5.9.4 Definitions and evaluations. 29
5.9.5 Recording . 30
5.10 Viewing direction dependence in a dark room . 30
5.10.1 Purpose . 30
5.10.2 Measuring conditions . 31
5.10.3 Measuring method . 31
5.10.4 Definitions and evaluations. 31
Annex A (informative) Calculation method of daylight colour gamut volume . 34
A.1 Purpose . 34
A.2 Procedure for calculating the colour gamut volume . 34
A.3 Surface subdivision method for CIELAB gamut volume calculation . 36
A.3.1 Purpose . 36
A.3.2 Assumptions . 36
A.3.3 Algorithm . 36
A.3.4 Software example . 36
Bibliography . 41

Figure 1 – Representation of the coordinate system used to specify the viewing or
measurement orientation . 9
Figure 2 – Standard measurement positions . 12
Figure 3 – Window pattern for cross-talk measurement . 20
Figure 4 – Example representation of the same primary colours in the CIE 1931 (left)
and CIE 1976 (right) chromaticity diagrams . 22
Figure 5 – Example of evaluation results for the colour gamut area on the a*b* plane
of the CIELAB colour space . 25
Figure 6 – An example of the range in colours produced by an sRGB display as
represented by the CIELAB colour space . 29
Figure 7 - Example of contrast ratio dependence on viewing direction . 32

– 4 – IEC 62679-3-3:2016 © IEC 2016
Figure A.1 – Analysis flow chart for calculating the colour gamut volume . 34
Figure A.2 – Graphical representation of the colour gamut volume for sRGB in the
CIELAB colour space . 35

Table 1 – Eigenvalues M and M for CIE daylight Illuminant D50 . 14
1 2
Table 2 – Input signals for CIELAB and CIE UCS u’v’ colour gamut area
measurements . 24
Table 3 – Example data of in-plane colour non-uniformity . 26
Table 4 – Example of minimum colours required for gamut volume calculation of a 3-
primary 8-bit display . 29
Table 5 – Measured tristimulus values for the minimum set of colours (see Table 4)
required for gamut volume calculation under the specified indoor illumination
conditions . 30
Table 6 – Calculated white point in the darkened room and indoor ambient condition . 30
Table 7 – Colour gamut volume in the CIELAB colour space . 30
Table 8 – Example format used for recording viewing direction performance . 33
Table A.1 – Tristimulus values of the sRGB primary colours . 35
Table A.2 – Example of sRGB colour set represented in the CIELAB colour space . 35
Table A.3 – Example of an sRGB colour gamut volume in the CIELAB colour space . 36

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRONIC PAPER DISPLAYS –
Part 3-3: Optical measuring methods for displays
with integrated lighting units

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard 62679-3-3 has been prepared by IEC technical committee 110:
Electronic display devices.
The text of this standard is based on the following documents:
CDV Report on voting
110/723/CDV 110/780/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 6 – IEC 62679-3-3:2016 © IEC 2016
A list of all parts in the IEC 62679 series, published under the general title Electronic paper
displays, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
ELECTRONIC PAPER DISPLAYS –
Part 3-3: Optical measuring methods for displays
with integrated lighting units

1 Scope
This part of IEC 62679 specifies the standard measurement conditions and measurement
methods for determining the optical performance of electronic paper display (EPD) devices
which have an operating integrated lighting unit (such as a front light). The scope of this
document is restricted to EPDs using segmented or matrix structures with either
monochromatic or colour type displays. The measurement methods are intended for EPDs
operated in a reflective mode with the integrated lighting unit (ILU) turned on in a dark or
indoor ambient lighting environment. Colour systems beyond three primaries are not covered
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 for this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 62679-1-1, Electronic paper displays – Part 1-1: Terminology
IEC 62679-3-1:2014, Electronic paper displays – Part 3-1: Optical measuring methods
IEC 61966-2-1, Multimedia systems and equipment – Colour measurement and management
– Part 2-1: Colour management – Default RGB colour space – sRGB
CIE 15, Colorimetry
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 62679-1-1,
IEC 60050-845, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
ILU
integrated lighting unit
light source integrated into an EPD device to provide supplementary illumination to
compensate for the lack of adequate ambient illumination

– 8 – IEC 62679-3-3:2016 © IEC 2016
3.1.2
ambient contrast ratio
contrast ratio of a display with both hemispherical diffuse and directional illumination incident
onto its surface used to simulate real lighting environments
Note 1 to entry: In this document, the ambient contrast ratio is determined with the ILU turned on in addition to the
ambient illumination incident on the display.
3.1.3
colour gamut volume
single number corresponding to the largest possible range of display colours (including all
possible mixtures of the primaries, white W and black K), described as a volume in a three-
dimensional colour space such as CIELAB
3.2 Abbreviated terms
CCT correlated colour temperature
CIE International Commission on Illumination
CIELAB CIE 1976 (L*a*b*) colour space
DUT device under test
EPD electronic paper display
ILU integrated lighting unit (e.g. a front lightguide plate)
LMD light-measuring device
RGB red, green, blue
SID Society for Information Display
sRGB a standard RGB colour space as defined in IEC 61966-2-1
4 Standard measuring conditions
4.1 Standard environmental measuring conditions
Optical and electro-optical measurements shall be carried out under standard environmental
conditions, at a temperature of 25 °C ± 3 °C, at a relative humidity of 25 % to 85 %, and at a
pressure of 86 kPa to 106 kPa. When different environmental conditions are used, they shall
be noted in the report.
4.2 Viewing direction coordinate system
The viewing direction is the direction under which the observer looks at the point of interest
on the device under test (DUT). During the measurement, the light-measuring device (LMD)
simulates the observer, by aiming the LMD at the point of interest on the DUT from the
viewing direction. The viewing direction is defined by two angles: the angle of inclination θ
(relative to the surface normal of the DUT) and the angle of rotation φ (also called azimuth
angle) as illustrated in Figure 1. Although the azimuth angle is measured in the counter-
clockwise direction, it is related to the directions on a clock face as follows: φ = 0° is the 3
o'clock direction ("right"), φ= 90° the 12 o'clock direction ("top"), φ = 180° the 9 o'clock
direction ("left") and φ = 270° the 6 o'clock direction ("bottom").

Z
θ
Y
12:00
φ
X
9:00 3:00
6:00
IEC
NOTE The viewing/measurement direction is specified by the angle of inclination and the angle of rotation
(azimuthal angle) in a polar coordinate system.
Figure 1 – Representation of the coordinate system used to specify
the viewing or measurement orientation
4.3 Standard lighting conditions
4.3.1 General comments and remarks on the measurement of electronic paper
displays
EPDs are often used as reflective displays, where the ambient external light reflected from the
active area is modulated. When there is insufficient external light, an ILU can be turned on to
provide an internal source of light for the optical modulation and display of information. This
document considers two cases: when the ILU is the only light source, and when it
supplements indoor ambient illumination. For these cases, an EPD with an operating ILU can
be treated as an emissive display, and any ambient lighting is a separate additive reflected
signal.
The measurement methods in this document are performed with the ILU turned on.
Subclause 4.3 describes a selection of standard lighting conditions for measuring the
performance characteristics of EPDs. EPDs may also be measured under other illumination
and detection geometries in addition to the standard geometries.
A warm-up time may be necessary for both the ILU and the illumination light source. The light
signal shall remain stable to within ±5 % over the course of the complete measurement.
4.3.2 Dark room conditions
EPDs are intended to be measured under controlled lighting conditions. Unwanted
background illumination shall be minimized, typically by illuminating the display in a dark room.
The dark room spectral radiance contribution from the background illumination, that is the
measured spectral radiance reflected off the DUT, shall be not more than 1/100 of the
spectral radiance from the device black state with the illumination source on. If this condition
is not satisfied, then background subtraction is required and it shall be noted in the report. In
addition, if the sensitivity of the LMD is inadequate to measure at these low levels, then the
lower limit of the LMD shall be noted in the report.
Unless stated otherwise, the standard background lighting conditions shall be those of the
dark room.
4.3.3 Standard indoor ambient illumination spectra
The following illumination conditions are specified for optical and electro-optical
measurements of reflective displays under indoor ambient illumination. A combination of two

– 10 – IEC 62679-3-3:2016 © IEC 2016
illumination geometries is generally used to simulate ambient indoor illumination [1, 2] .
Uniform hemispherical diffuse illumination will be used to simulate the background lighting in
a room, with any rays from luminaires or sunlight blocked from directly illuminating the screen. A
directed light source in a dark room will simulate the effect of directed illumination on a
display by a luminaire in a room.
The following illumination conditions shall be used to simulate indoor display viewing
environments:
• Uniform hemispherical diffuse illumination – Use a spectrally smooth broadband light
source to photometrically approximate CIE standard illuminant A, CIE standard
illuminant D65, or CIE illuminant D50 as defined in CIE 15. Better accuracy can be
obtained by performing spectral measurements. For spectral measurements, a
spectrally smooth broadband light source (such as an approximation to CIE standard
illuminant A) shall be used. A measurement of the spectral reflectance factor using a
broad light source (such as illuminant A) enables the indoor photopic and colour
characteristics to be calculated later for the desired reference spectra (for example
CIE illuminant D65). The performance characteristics shall be calculated using 300 lx
for an indoor reading environment [3]. The actual hemispherical diffuse reflectance
factor measurement may require higher illumination levels for better measurement
accuracy. The results are then scaled down to the required illumination levels.
• Directed illumination – The same source spectra shall be used as with hemispherical
diffuse illumination. The indoor room photopic and colour characteristics shall be
calculated using directed illumination of 200 lx incident on the display surface for an
indoor reading environment with the display in the vertical orientation. The actual
reflectance factor measurement may require higher illumination levels for better
measurement accuracy. The results are then scaled down to the required illumination levels.
The directed source shall be 45° above the surface normal (θ = 45°) and have an
s
angular subtense of no more than 5°. The angular subtense is defined as the full angle
span of the light source from the centre of the display’s measurement area.
Other illumination levels may be used in addition to those defined above for calculating the
ambient contrast ratio under indoor illumination conditions.
For indoor photopic and colorimetric calculations from spectral reflectance factor
measurements, the relative spectral distributions of CIE illuminants A, D50, and D65 tabulated
in CIE 15 shall be used. Additional CIE daylight illuminants shall be determined using the
appropriate eigenfunctions, as defined in CIE 15.
The UV region (< 380 nm) of the light source shall be cut off by a UV blocking filter. When
high light-source illumination levels are used, an infrared-blocking filter is recommended to
minimize device heating.
4.3.4 Standard illumination geometries
One or more of three types of illumination geometries shall be used for determining the
performance of the EPD: directional illumination, ring light illumination, and hemispherical
illumination. The standard configurations for implementing these illumination geometries are
defined in IEC 62679-3-1:2014, 4.3.4. Additional illumination geometries may also be used.
The details of the illumination geometry used for a given measurement shall be reported.
Further guidance on the proper implementation of these illumination geometries is given in the
SID Information Display Measurements Standard [1].
___________
Numbers in square brackets refer to the Bibliography.

4.4 Adjustment of the EPD
The EPD (including the ILU) shall be adjusted to nominal product design values, and shall be
noted in detail in the report. When there are no levels specified, the maximum contrast level
shall be used and the settings noted in the report. These adjustments shall be held constant
for all measurements, unless stated otherwise.
If it can be demonstrated that the reflection properties of the EPD are the same with the ILU
off or on, then the reflection measurements may be performed with the ILU off.
4.5 Standard conditions of measuring equipment
Standard equipment conditions are given in IEC 62679-3-1:2014, 4.4. Any deviations from
these conditions shall be noted in the report.
Measurements shall be started after the EPD, the source illumination, and the measuring
instruments achieve stability.
4.6 Working standards and references
The use of specular and diffuse reflectance standards for reflection measurements are given
in IEC 62679-3-1:2014, 4.5.
The terms luminous reflectance and luminous reflectance factor shall be abbreviated to
reflectance and reflectance factor, respectively.
4.7 Standard locations of measurement field
4.7.1 Matrix displays
Luminance, spectral distribution and/or tristimulus measurements may be taken at several
specified positions on the DUT surface. To this end, the front view of the display is divided
into 25 identical imaginary rectangles (see Figure 2). Unless otherwise specified,
measurements are carried out in the centre of each rectangle. The rectangles are numbered
starting from the centre, and progressing towards the edges in a clock-wise spiral fashion.
Care shall be taken to ensure that the measuring fields on the display do not overlap.
Positioning of the measuring field at the prescribed positions in the horizontal (V) and
vertical (H) directions shall be to within 7% of H and V, respectively. The display or detector
shall be translated in the horizontal and vertical directions to perform measurements at the
desired display positions, with all measurements taken normal to the screen. Any deviation
from the above standard positions shall be reported.

– 12 – IEC 62679-3-3:2016 © IEC 2016
P P P P P
23 24 9 10 11
P P P P P
22 8 1 2 12
P P P P
P
21 7 0 3
P P P P P
20 6 4
5 14
P P P P P
19 18 17 16 15
(1/10)V
(3/10)H
(1/10)H
(5/10)H
IEC
NOTE Standard measurement positions are at the centres of all rectangles P to P . The height and width of
0 24
each rectangle are 20 % of display height and width, respectively.
Figure 2 – Standard measurement positions
4.7.2 Segment displays
Standard measurement positions are the same as those prescribed for matrix displays above.
However, for segment displays, all measurements shall be performed at the centre of a
segment, and the chosen segment should be as close as possible to the centre of the
designated rectangle. Thus, when measurements on position P (i = 0 to 24) are requested,
i
the geometrical centre of the segment closest to the centre of box P should be used for the
i
positioning of the detector. Any deviation from the above standard positions shall be added to
the detail specification.
The measuring field shall be contained entirely within the segment.
5 Optical measuring methods
5.1 Reflection measurements
5.1.1 General
The purpose of this method is to determine the reflectance factor of an EPD with an ILU on
under defined illumination conditions. If it can be demonstrated that the reflection properties
of the EPD are the same with the ILU off or on, then the reflection measurements may be
performed with the ILU off.
Spectral reflectance factor measurements are generally preferred. Luminous reflectance
factor measurements can be used to calculate photometric quantities (such as ambient
contrast ratio), but only when the source illumination closely approximates the intended
illuminant used in the analysis [4].
5.1.2 Measuring conditions
a) Apparatus:
(5/10)V
(3/10)V
Driving signal equipment; an integrating sphere, sampling sphere, or hemisphere; and a
directed light source should be used. For spectral measurements, a spectroradiometer
that can measure luminance and spectral radiance is needed, as well as a white diffuse
reflectance standard with a known hemispherical diffuse spectral reflectance and a
directed spectral reflectance factor calibrated for the intended measurement geometry. For
photometric measurements, a detector is required that can measure luminance, and a
white diffuse reflectance standard is required with a known luminous hemispherical diffuse
reflectance and a directed reflectance factor calibrated for the intended measurement
geometry and source spectra.
b) Illuminance condition:
The standard directional, ring light, or hemispherical illumination conditions shall be used,
as defined in IEC 62679-3-1:2014, 4.3.4. The illumination spectra should approximate CIE
Illuminant D50 or D65. Otherwise, a stable and spectrally smooth broadband visible light
source (e.g. incandescent lamp) shall be used. The illumination/detection geometry used,
and the light source CCT, shall be reported.
5.1.3 Measuring the hemispherical diffuse reflectance
a) Turn on the ILU. The ILU may be turned off if it can be demonstrated that the
hemispherical diffuse reflection properties of the EPD do not depend on the ILU's
operational state. In that case, steps f), g), and h) are not necessary.
b) Place the display in an integrating sphere or against the sample port of a sampling sphere,
as indicated in IEC 62679-3-1:2014, 4.3.4.4. Turn on the integrating sphere or sampling
sphere hemispherical diffuse illumination to the desired CCT. Allow enough time for the
EPD and light source to stabilize. Any change in sphere illuminance can be monitored by
a photometric detector attached to the sphere.
c) Set the DUT to display a full screen of the desired colour Q (usually red, green, blue,
black, or white) at the highest reflective level, where Q is a variable for the colour used.
d) Align the LMD through the measurement port, focused on the display surface at the
desired display position, and at an 8° to 10° angle to the display surface normal. Unless
stated otherwise, the LMD measurement field is located at the screen's centre. Measure
the spectral radiance L (λ) or luminance L at the desired measurement
Q,hemi-on Q,hemi-on
position on the display with the hemispherical illumination turned on, where L
Q,hemi-on
=Y for a colorimeter. For spectral measurements, the display luminance L
Q,hemi-on Q,hemi-on
can be calculated from the spectral radiance L (λ) using the following relation:
Q,hemi-on
(1)
L = 683 L(λ)V(λ)dλ
∫
λ
where V(λ) is the photopic luminous efficiency function as defined in CIE 15.
NOTE In this document, spectral measurements, such as spectral radiance, will be specifically identified by their
wavelength dependence (e.g. L (λ)), whereas their photometric equivalent luminance will have no explicit
Q,hemi-on
wavelength dependence (e.g. L ).
Q,hemi-on
e) Align the LMD with the centre of the calibrated white diffuse reflectance standard and
measure its spectral radiance S (λ) or luminance S with the display set to
Q,hemi-on Q,hemi-on
the desired colour Q. For the sampling sphere case, the S (λ) and S are
Q,hemi-on Q,hemi-on
the spectral radiance and luminance, respectively, measured from the sphere wall
adjacent to the sample port. The sphere wall has to be calibrated against the diffuse
reflectance standard prior to the measurement. For this, the spectral reflectance of the
wall is determined by placing the reflectance standard in the sample port, by measuring
the spectral radiance of the standard and the adjacent wall, and by assuming that the
diffuse reflectance of the standard and wall are proportional to the respective measured
spectral radiance or luminance (see IEC 62679-3-1:2014, 4.3.4.4).
f) If it has previously been demonstrated that the hemispherical diffuse reflection properties
of the EPD are the same with the ILU off or on, then the reflection measurements may be
performed with the ILU off. In that case, the next two steps may be skipped. Otherwise,
turn off the integrating sphere or the sampling sphere hemispherical diffuse illumination.
This may be accomplished by turning off the light source. If the sphere light is input by a

– 14 – IEC 62679-3-3:2016 © IEC 2016
portable source (such as an optical fibre bundle), then the hemispherical illumination light
can be turned off by disconnecting it at the light-source end so that the interior
configuration of the sphere is not changed.
g) Measure the spectral radiance S (λ) or luminance S of the calibrated white
Q,hemi-off Q,hemi-off
diffuse reflectance standard (or the calibrated wall of the sampling sphere) with the
hemispherical illumination turned off.
h) Align the LMD with the centre of the display. Measure the screen spectral radiance
L (λ) or luminance L in the centre of the display with the hemispherical
Q,hemi-off Q,hemi-off
illumination turned off.
i) Calculate the hemispherical diffuse spectral reflectance ρ (λ), or luminous hemispherical
Q
diffuse reflectance ρ , of the display at the desired colour Q for the measured
Q
illumination/detection geometry.
For spectral measurements, the following relation is used:
[L (λ) - L (λ)]
Q,hemi-on Q,hemi-off
ρ (λ) = ρ (λ) (2)
Q std
[S (λ) - S (λ)]
Q,hemi-on Q,hemi-off
where ρ (λ) is the known hemispherical spectral reflectance for the white diffuse
std
reflectance standard, or sampling sphere wall, in the same measurement geometry. If the
hemispherical diffuse reflection properties of the EPD do not depend on the ILU's
operational state, then the reflection measurements can be performed with the ILU off,
and the L (λ) and S (λ) terms will both be zero. The luminous hemispherical
Q,hemi-off Q,hemi-off
diffuse reflectance of a display at the desired hemispherical diffuse illumination CIE
spectra E (λ) is determined using the spectral reflectance ρ (λ) in the following
CIE,hemi Q
equation:
ρλ()E ()λ Vd()λ λ
Q CIE,hemi
∫
λ
ρ = (3)
Q
E ()λ Vd()λ λ
CIE,hemi
∫
λ
CIE illuminants A, D50, and D65 should be used to simulate indoor hemispherical diffuse
illumination. The relative spectral distributions of CIE illuminant A, D50, and D65 tabulated
in CIE 15 shall be used. If additional illuminants are desired, the following relation from
CIE 15 shall be used:
E (λ) = E (λ) + M E (λ) + M E (λ) (4)
CIE 0 1 1 2 2
where the E , E , and E eigenfunctions are tabulated in CIE 15, and M and M are
0 1 2 1 2
eigenvalues defined in the same document. For example, M and M are given in Table 1
1 2
in the case of D50.
Table 1 – Eigenvalues M and M for CIE daylight Illuminant D50
1 2
Correlated colour temperature
Eigenvalues
5 000 K
M –1,040 1
M
0,366 66
For luminance measurements, the photometric equivalent of Equation (2) is used:

-LL 
Q,hemi-on Q,hemi-off

ρρ= (5)
Q std
-SS 
Q,hemi-on Q,hemi-off

This relation is only valid when the measurement is made with the same geometry and
spectral distribution at that used to calibrate the white diffuse reflectance standard ρ . In
std
addition, any display performance calculation using the luminous hemispherical diffuse
reflectance by the photometric method in Equation (5) is only valid for light sources with
similar spectra and geometry. If the ILU was turned off in the prior measurements, then
and S terms will both be zero.
the L
Q,hemi-off Q,hemi-off
To ensure measurement integrity, the reflected component of the sphere illumination shall
be much greater than the display emission (i.e. L (λ)>>L (λ)). The same
Q,hemi-on Q,hemi-off
applies for the photometric equivalents in Equation (5).
j) Report the CCT of the display test illumination, ρ , the detector parameters (incident
Q
angle, measurement field angle, and distance to sample) and illumination source geometry
used in the measurements in the test report.
5.1.4 Measuring the reflectance factor for a directed light source
a) Turn on the ILU. However, the ILU may be turned off if it can be demonstrated that the
directional reflection properties of the EPD do not depend on the ILU's operational state. If
this is the case, step d) is not
...