ISO/TR 9241-313:2025

Ergonomics of human-system interaction — Part 313: Optical measurement methods for reflective displays

This document provides background information and a validated methodology for optical reflection measurements for flat direct view electronic displays. This document includes calculation methods for using measured reflection coefficients to predict display performance in specific indoor and outdoor ambient illumination conditions. This document demonstrates optical measurements of electrophoretic displays (EPDs), as a reflective electronic visual display technology; many methods are also applicable to other appropriate reflective and emissive displays. This document does not include a methodology for ergonomics evaluation.

Ergonomie de l’interaction homme-système — Partie 313: Méthodes de mesure optique pour écrans réfléchissants

General Information

• Status: Published
• Publication Date: 14-Jul-2025
• ICS: 13.180 - Ergonomics
• ICS: 35.180 - IT Terminal and other peripheral equipment
• Technical Committee: ISO/TC 159/SC 4 - Ergonomics of human-system interaction
• Drafting Committee: ISO/TC 159/SC 4/WG 2 - Visual display requirements
• Current Stage: 6060 - International Standard published
• Start Date: 15-Jul-2025
• Due Date: 05-Oct-2025
• Completion Date: 15-Jul-2025

Standards Content (Sample)

Technical
Report
ISO/TR 9241-313
First edition
Ergonomics of human-system
2025-07
interaction —
Part 313:
Optical measurement methods for
reflective displays
Ergonomie de l’interaction homme-système —
Partie 313: Méthodes de mesure optique pour écrans
réfléchissants
Reference number
© ISO 2025
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions .1
3.2 Abbreviated terms .3
4 Reflective display technology . 3
5 General optical measurement methodology . 4
5.1 Spectral radiance of display in ambient illumination .4
5.2 General concept of ambient illumination .5
5.2.1 Outdoor ambient illumination . .7
5.2.2 Indoor ambient illumination .7
5.3 Theory of reflected spectral radiance of display in ambient illumination .8
5.4 Components of spectral radiance reflected by the display .10
5.4.1 General concept of reflection in paper, emissive displays and reflective displays .10
5.4.2 Coordinate system for illumination and viewing direction .11
5.4.3 Bi-directional reflection distribution function (BRDF) of the display . 12
5.4.4 Reflection measurement geometries .14
6 Measurement methods for display reflection .16
6.1 General .16
6.2 Definitions and symbols .16
6.3 Calibration standards and measurement samples .17
6.3.1 Diffuse white reflectance standard.17
6.3.2 Specular reflectance standard .17
6.3.3 Diagnostic reflection samples .18
6.3.4 Reflective display samples .18
6.4 Measurement methods and examples of bi-directional reflection distribution function
(BRDF) .18
6.4.1 General .18
6.4.2 Imaging sphere .19
6.4.3 Reflection conoscope .24
6.4.4 Gonioreflectometer . 26
6.4.5 Conclusions of bi-directional reflection distribution function (BRDF)
measurements .32
6.5 Measuring specular reflectance under illumination from a variable aperture source . 33
6.5.1 General concept of variable aperture source . 33
6.5.2 Theory of the extended source as superposition of point sources . 34
6.5.3 Theory of separating specular and diffuse reflection using a variable aperture
source (VAS) . 36
6.5.4 Theory of separating the haze reflection using an annulus source . . 38
6.5.5 Measurement methodology of variable aperture source reflection .41
6.5.6 Measuring variable aperture source reflection of diagnostic reflection samples . 44
6.5.7 Measuring variable aperture source reflection of EPDs. 48
6.5.8 Separating the specular and diffuse reflection components . 54
6.5.9 Estimating the source-size dependence of haze . 56
6.5.10 Conclusions of reflection measurements using variable aperture and annulus
sources . 64
6.6 Measuring off-specular reflectance under directional illumination . 65
6.6.1 Reflectance under directional illumination . 65
6.6.2 Viewing direction dependence of reflectance under directional illumination . 65
6.7 Measuring reflectance under hemispherical-diffuse illumination .67
6.7.1 Reflectance under hemispherical-diffuse illumination.67

iii
6.7.2 Viewing direction dependence of reflectance under hemispherical-diffuse
illumination. 69
6.8 Measuring reflectance under off-specular directional and hemispherical-diffuse
illumination . 73
6.8.1 General . 73
6.8.2 Deriving photometric parameters from measured spectral distributions . 73
6.8.3 Reflectance and contrast ratio (CR) of electrophoretic displays (EPDs) .74
7 Prediction of display contrast in ambient illumination .77
7.1 Components of reflected spectral radiance. 77
7.2 Prediction of display contrast . 78
7.2.1 Display contrast under ambient illumination without unwanted reflection . 78
7.2.2 Display contrast under ambient illumination in the presence of unwanted
reflection . 83
8 Conclusions .88
Bibliography .89

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 04,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies c
...

FINAL DRAFT
Technical
Report
ISO/DTR 9241-313
ISO/TC 159/SC 4
Ergonomics of human-system
Secretariat: BSI
interaction —
Voting begins on:
2025-03-28
Part 313:
Optical measurement methods for
Voting terminates on:
2025-05-23
reflective displays
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/DTR 9241-313:2025(en) © ISO 2025

FINAL DRAFT
ISO/DTR 9241-313:2025(en)
Technical
Report
ISO/DTR 9241-313
ISO/TC 159/SC 4
Ergonomics of human-system
Secretariat: BSI
interaction —
Voting begins on:
Part 313:
Optical measurement methods for
Voting terminates on:
reflective displays
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2025
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DTR 9241-313:2025(en) © ISO 2025

ii
ISO/DTR 9241-313:2025(en)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions .1
3.2 Abbreviated terms .3
4 Reflective display technology . 3
5 General optical measurement methodology . 4
5.1 Spectral radiance of display in ambient illumination .4
5.2 General concept of ambient illumination .5
5.2.1 Outdoor ambient illumination . .7
5.2.2 Indoor ambient illumination .7
5.3 Theory of reflected spectral radiance of display in ambient illumination .8
5.4 Components of spectral radiance reflected by the display .10
5.4.1 General concept of reflection in paper, emissive displays and reflective displays .10
5.4.2 Coordinate system for illumination and viewing direction .11
5.4.3 Bi-directional reflection distribution function (BRDF) of the display . 12
5.4.4 Reflection measurement geometries .14
6 Measurement methods for display reflection .16
6.1 General .16
6.2 Definitions and symbols .16
6.3 Calibration standards and measurement samples .17
6.3.1 Diffuse white reflectance standard.17
6.3.2 Specular reflectance standard .17
6.3.3 Diagnostic reflection samples .18
6.3.4 Reflective display samples .18
6.4 Measurement methods and examples of bi-directional reflection distribution function
(BRDF) .18
6.4.1 General .18
6.4.2 Imaging sphere .19
6.4.3 Reflection conoscope .24
6.4.4 Gonioreflectometer . 26
6.4.5 Conclusions of bi-directional reflection distribution function (BRDF)
measurements .32
6.5 Measuring specular reflectance under illumination from a variable aperture source . 33
6.5.1 General concept of variable aperture source . 33
6.5.2 Theory of the extended source as superposition of point sources . 34
6.5.3 Theory of separating specular and diffuse reflection using a variable aperture
source (VAS) . 36
6.5.4 Theory of separating the haze reflection using an annulus source . . 39
6.5.5 Measurement methodology of variable aperture source reflection .41
6.5.6 Measuring variable aperture source reflection of diagnostic reflection samples .45
6.5.7 Measuring variable aperture source reflection of EPDs. 49
6.5.8 Separating the specular and diffuse reflection components . 55
6.5.9 Estimating the source-size dependence of haze . 58
6.5.10 Conclusions of reflection measurements using variable aperture and annulus
sources . 65
6.6 Measuring off-specular reflectance under directional illumination . 66
6.6.1 Reflectance under directional illumination . 66
6.6.2 Viewing direction dependence of reflectance under directional illumination . 66
6.7 Measuring reflectance under hemispherical-diffuse illumination . 68
6.7.1 Reflectance under hemispherical-diffuse illumination. 68

iii
ISO/DTR 9241-313:2025(en)
6.7.2 Viewing direction dependence of reflectance under hemispherical-diffuse
illumination.70
6.8 Measuring reflectance under off-specular directional and hemispherical-diffuse
illumination . 73
6.8.1 General . 73
6.8.2 Deriving photometric parameters from measured spectral distributions . 73
6.8.3 Reflectance and contrast ratio (CR) of electrophoretic displays (EPDs) . 75
7 Prediction of display contrast in ambient illumination .77
7.1 Components of reflected spectral radiance. 77
7.2 Prediction of display contrast . 79
7.2.1 Display contrast under ambient illumination without unwanted reflection . 79
7.2.2 Display contrast under ambient illumination in the presence of unwanted
reflection . 83
8 Conclusions .88
Bibliography .90

iv
ISO/DTR 9241-313:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any clai
...

© ISO 9241 – All rights reserved
ISO TR9241/DTR 9241-313(X)
ISO/TC 159/SC 04/WG 2 4
Secretariat: XXXX BSI
Title (Date: 2025-03-13
Ergonomics of human-system interaction —
Part 313:
Optical measurement methods for reflective displays)

WD/CD/DIS/FDIS stage
Warning for WDs and CDs
This document is not an ISO International Standard. It is distributed for review and comment. It is subject to
change without notice and may not be referred to as an International Standard.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of
which they are aware and to provide supporting documentation.

ISO #####-#:####(X)
2 © ISO #### – All rights reserved

ISO/DTR 9241-313(X:(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Fax: [phone]
EmailE-mail: [e-mail]
Website: www.iso.orgwww.iso.org
Published in Switzerland
© ISO 9241 2025 – All rights reserved
iii
ISO/DTR 9241-313(X:(en)
Contents
Foreword . v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 1
3.1 Terms and definitions . 1
3.2 Abbreviated terms . 3
4 Reflective display technology . 3
5 General optical measurement methodology . 5
5.1 Spectral radiance of display in ambient illumination . 5
5.2 General concept of ambient illumination . 6
5.3 Theory of reflected spectral radiance of display in ambient illumination . 9
5.4 Components of spectral radiance reflected by the display . 12
6 Measurement methods for display reflection . 20
6.1 General . 20
6.2 Definitions and symbols . 20
6.3 Calibration standards and measurement samples . 21
6.4 Measurement methods and examples of bi-directional reflection distribution function
(BRDF) . 22
6.5 Measuring specular reflectance under illumination from a variable aperture source . 44
6.6 Measuring off-specular reflectance under directional illumination . 94
6.7 Measuring reflectance under hemispherical-diffuse illumination . 96
6.8 Measuring reflectance under off-specular directional and hemispherical-diffuse
illumination . 105
7 Prediction of display contrast in ambient illumination . 110
7.1 Components of reflected spectral radiance . 110
7.2 Prediction of display contrast . 113
8 Conclusions. 128
Bibliography . 130

To update the Table of Contents please select it and press "F9".
© ISO 9241 2025 – All rights reserved
iv
ISO/DTR 9241-313(X:(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documentsdocument should be noted. This document was drafted in accordance with the editorial rules
of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO had not received notice of (a) patent(s) which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which may be
obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for
identifying any or all such patent rights. Details of any patent rights identified during the development of the
document will be in the Introduction and/or on the ISO list of patent declarations received (see ).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 04,
Ergonomics of human-system interaction.
A list of all parts in the ISO 9241 series can be found on the ISO website.
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 9241 2025 – All rights reserved
v
ISO/DTR 9241-313(X:(en)
Introduction
This document provides an overview of recent research on applying the optical reflection measurement
methodology for flat direct view electronic displays to electrophoretic displays (EPDs). This document
contributes background to revisions of ISO 9241-307,, ISO 9241-305 and ISO 9241-303 to accommodate,
providing information regarding reflective displays in ambient indoor and outdoor illumination environments
,
defined by CIE 015:2018 and CIE S017:2020.
Reflective displays convey information by modulating the reflected light, using independently controlled
segments or pixels. Any reflective display performs the following two basic optical functions:, either equally
for all wavelengths achromatically or for selective wavelengths chromatically:
— reflecting ambient illumination towards the human observer, and ;
—modulating the amount and spectral distribution of the reflected light, either equally for all wavelengths
achromatically or for selective wavelengths chromatically. .
For example, EPDEPDs use electrically charged pigments to reflect and modulate light. Opaque white pigments
with near-Lambertian reflection characteristics form the paper-like, diffuse reflecting background. Light-
absorbing black pigments attenuate the reflected light as traditional ink does on paper. These properties
differentiate EPDs from other display technologies by its paper-like appearance that offers a wide range of
viewing directions and sunlight readability. Other properties are low power consumption and the absence of
flicker. Other known reflective display technologies use reflectors with metallic, mirror or retroreflective
characteristics, combined with diffusers, achromatic reflection modulators (for example liquid crystal
shutters) and a colour filter array (CFA). EPDs are used in static and mobile applications including e-readers,
wearables and signage for both indoor and outdoor applications.
A reflective display needsmust have ambient illumination for the displayed information to be visible. Ambient
illumination has directional and diffuse components. In outdoor environments, direct sunlight is the
directional component, and skylight the diffuse component. In indoor environments, the diffuse component is
dominant, e.g. diffuse daylight through windows and light is scattered by walls and ceiling. In addition,
specular reflection of light sources of various sizes (from small luminaires to large windows) has the potential
to obliterate the information on display screens. This document will explainexplains how to separately
measure the display’s reflection characteristics under specific measurement illumination conditions, e.g. off-
specular directional, hemispherical-diffuse, and specular variable aperture source (VAS) illumination. The
three fundamental reflection components – (specular, haze, and Lambertian –) are measured separately and
as a function of illumination source size. Once the reflection coefficients for each illumination geometry are
measured, the reflected luminance from each illumination component is determined, and the infinite variety
of ambient multi-source illumination is expressed as a summation of reflected illumination components from
these sources. The total spectral radiance entering the observer’s eye when viewing a display is then predicted
as a summation of all the ambient light components reflected into the direction of viewing. The contributions
from each source are scaled according to their irradiance spectra for specific in- and outdoor illumination
environments.
This document includes examples of standardized indoor and outdoor illumination conditions, and useuses
EPDs to illustrate the measurement methods.
© ISO 9241 2025 – All rights reserved
vi
ISO 9241-313(X)
© ISO ####9241 – All rights reserved vii

ISO/DTR 9241-313:(en)
Title (Ergonomics of human-system interaction — —
Part 313:
Optical measurement methods for reflective displays)
1 Scope
This document givesprovides background information and a validated methodology for optical reflection
measurements for flat direct view electronic displays. This document includes calculation methods for using
measured reflection coefficients to predict display performance in specific indoor and outdoor ambient
illumination conditions.
This document demonstrates optical measurements of electrophoretic displays (EPDs), as a reflective
electronic visual display technology; many methods will beare also applicable to other appropriate reflective
and emissive displays. This document does not include a methodology for ergonomics evaluation.
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 9241-302, Ergonomics of human-system interaction — Part 302: Terminology for electronic visual displays
ISO 9241-303, Ergonomics of human-system interaction — Part 303: Requirements for electronic visual displays.
ISO 9241-305:2008, Ergonomics of human-system interaction — Part 305: Optical laboratory test methods for
electronic visual displays.
ISO 9241-307, Ergonomics of human-system interaction — Part 307: Analysis and compliance test methods for
electronic visual displays.
ISO/CIE 23539:2023(E) Photometry — The CIE system of physical photometry.
3 Terms, definitions and abbreviated terms
4.13.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9241-302, ISO 9241-303, ISO 9241-
305 and the following apply.
ISO and IEC maintain terminologicalterminology 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/
4.1.13.1.1
reflective display
electronic disp
...