SIST EN ISO 9241-7:2001
(Main)Ergonomic requirements for office work with visual display terminals (VDTs) - Part 7: Requirements for display with reflections (ISO 9241-7:1998)
Ergonomic requirements for office work with visual display terminals (VDTs) - Part 7: Requirements for display with reflections (ISO 9241-7:1998)
IEC/TS 62600-100:2012(E) provides a method for assessing the electrical power production performance of a Wave Energy Converter (WEC), based on the performance at a testing site. Provides a systematic method which includes:
- measurement of WEC power output in a range of sea states;
- WEC power matrix development;
- an agreed framework for reporting the results of power and wave measurements.
Ergonomische Anforderungen für Bürotätigkeiten mit Bildschirmgeräten - Teil 7: Anforderungen an visuelle Anzeigen Bezüglich Reflexionen (ISO 9241-7:1998)
Dieser Teil der ISO 9241 legt Anforderungen an die Bildqualität von Bildschirmgeräten fest, die in heller Umgebung benutzt werden, durch die Reflexionen auf der Bildschirmoberfläche verursacht werden können. Die Forderungen sind als Leistungs- oder als Entwurfsmerkmale angegeben, und Prüfmethoden werden dargestellt.
Exigences ergonomiques pour travail de bureau avec terminaux a écrans de visualisation (TEV) - Partie 7: Exigences d'affichage concernant les réflexions (ISO 9241-7:1998)
Ergonomic requirements for office work with visual display terminals (VDTs) - Part 7: Requirements for display with reflections (ISO 9241-7:1998)
General Information
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Standards Content (Sample)
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SIST EN ISO 9241-7:2001
INTERNATIONAL ISO
STANDARD 9241-7
First edition
1998-04-01
Ergonomic requirements for office work
with visual display terminals (VDTs) —
Part 7:
Requirements for display with reflections
Exigences ergonomiques pour travail de bureau avec terminaux à écrans
de visualisation (TEV) —
Partie 7: Exigences d'affichage concernant les réflexions
A Reference number
ISO 9241-7:1998(E)
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ISO 9241-7:1998(E)
Contents Page
1 Scope . 1
2 Normative references . 1
3 Definitions and symbols . 2
.......................................................................
4 Guiding principles 7
5 Performance objectives . 7
6 Requirements. 7
7 Measurements and calculations . 9
8 Compliance. 16
Annex A: Alternative test method. 18
Annex B: Graphical report format. 22
Annex C: Worked example. 26
Annex D: Bibliography . 31
© ISO 1998
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 the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet central@iso.ch
X.400 c=ch; a=400net; p=iso; o=isocs; s=central
Printed in Switzerland
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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.
Draft International Standards adopted by the technical committees are
circulated to the member bodies for voting. Publication as an International
Standard requires approval by at least 75 % of the member bodies casting
a vote.
International Standard ISO 9241-7 was prepared by Technical Committee
ISO/TC 159, Ergonomics, Subcommittee SC 4, Ergonomics of human
system interaction.
ISO 9241 consists of the following parts, under the general title Ergonomic
requirements for office work with visual display terminals (VDTs):
— Part 1: General Introduction
—
Part 2: Guidance on task requirements
—
Part 3: Visual display requirements
—
Part 4: Keyboard requirements
—
Part 5: Workstation layout and postural requirements
—
Part 6: Environmental requirements
—
Part 7: Requirements for display with reflections
—
Part 8: Requirements for displayed colours
—
Part 9: Requirements for non-keyboard input devices
—
Part 10: Dialogue principles
—
Part 11: Guidance on usability
—
Part 12: Presentation of information
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—
Part 13: User guidance
—
Part 14: Menu dialogues
—
Part 15: Command dialogues
— Part 16: Direct manipulation dialogues
— Part 17: Form-filling dialogues
Annexes A, B, C and D of this part of ISO 9241 are for information only.
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Introduction
Visual display terminals (VDTs) are subject to reflections of environmental
luminance and illuminance from the display device surfaces. Under some
conditions, the reflections become disturbing to the user and affect both
comfort and task performance. The objective of this part of ISO 9241 is to
maintain usable and acceptable VDT image quality in luminous environ-
ments that can cause reflections from the screen.
The document is intended for evaluators and users of VDTs. It is intended
to be used with ISO 8995, ISO 9241-3, ISO 9241-6 and ISO 9241-8 to
provide guidance for the visual ergonomics of the VDT workplace.
Compliance with this part of ISO 9241 is dependent on the hardware
characteristics of the VDT, except for polarity that can be application-
dependent.
This part of ISO 9241 contains requirements and methods for
measurement of the image quality of VDTs used in luminous environments
that can cause specular and diffuse reflections from the screen.
ISO 9241-3 and ISO 9241-8 contain requirements that deal with luminance
and luminance ratios for VDT images measured under conditions that
exclude specular reflections. These parts of ISO 9241 interact with this
part of ISO 9241. VDTs that meet the interacting requirements and
recommendations of ISO 9241-3 and ISO 9241-8 do not necessarily meet
those of this part ISO 9241 and vice versa.
ISO 9241-6 and ISO 8995 contain specific recommendations concerning
design of the workplace luminous environment to minimize sources of
glare. The luminous environment conditions used to determine compliance
with this part of ISO 9241 are drawn from, or are consistent with
recommendations and requirements of these International Standards. The
luminous environment values used to determine compliance to this part of
ISO 9241 do not constitute specific recommendations or requirements for
workplace lighting.
The burden of a visually acceptable VDT workplace is a tradeoff between
the display hardware and the VDT environment. To acknowledge that
tradeoff, compliance with this part of ISO 9241 has been developed in
three classes, each with rules for decision based on environmental
assumptions.
Although the decision rules are not expected to be exactly duplicated in the
workplace environment, they do correspond approximately to general types
of workplace environment to which VDTs are expected to be suitable:
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Class Environment
I suitable for general office use
II suitable for most, but not all, office environments
III requiring a specially controlled luminous environment for use
An alternative test method is provided for VDTs whose characteristics
preclude use of the quantitative test method.
NOTE — ISO 13406 extends the definitions, requirements, and test method of
this part of ISO 9241 for flat panels whose colour and/or luminance contrast is
strongly dependent on the direction from which they are viewed, and whose
reflection characteristics can vary with the logical state of the screen.
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Ergonomic requirements for office work with visual display
terminals (VDTs) —
Part 7:
Requirements for display with reflections
1 Scope
This part of ISO 9241
— establishes image quality requirements for VDTs used in luminous environments that may cause reflections
from the screen. The requirements are stated as performance or design specifications, and test methods are
provided.
— applies to the ergonomic design of direct-view electronic displays for office tasks, including such activities as
data entry, text processing and interactive inquiry. Office tasks are performed indoors, without exposure to
direct sunlight. The recommendations can possibly be appropriate for other tasks, including process control,
graphic design and computer-aided design, but their applicability has not been established.
— applies to monochrome and multicolour displays. The following displays and similar types are excluded from
the scope of this part of ISO 9241: multi-user projection displays, transparent displays and virtual image
displays.
— applies to VDTs for which its test method is suitable. The test method is limited to VDTs whose colour and/or
luminance contrast does not vary strongly as a function of the viewing direction, and whose reflection properties
do not vary as a function of the logical state of the screen. The test method is suitable for emissive VDT
technologies, such as cathode ray tubes, and some flat panels.
NOTE — VDTs using display devices for which the test method of this part of ISO 9241 is not suitable (for example, liquid
crystal displays) are directed to ISO 13406-2.
2 Normative references
The following standards contain provisions which, through reference in the text, constitute provisions of this part of
ISO 9241. At the time of publication, the editions indicated were valid. All standards are subject to revision, and
parties to agreements based on this part of ISO 9241 are encouraged to investigate the possibility of applying the
most recent edition of the standards indicated below. Members of ISO and IEC maintain registers of currently valid
International Standards.
ISO 9241-3:1992. Ergonomic requirements for office work with visual display terminals (VDTs) — Part 3: Visual dis-
play requirements.
ISO 9241-8:1997, Ergonomic requirements for office work with visual display terminals (VDTs) — Part 8: Require-
ments for displayed colours.
CIE 17.4: 1989, International Lighting Vocabulary.
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3 Definitions and symbols
3.1 Definitions
For purposes of this part of ISO 9241, the definitions given in ISO 9241-3 (except in 3.1.5) and the following
definitions apply.
3.1.1 dark room: Room in which the only sources of light are the VDT under test and the prescribed sources of
luminance or illuminance.
3.1.2 extended source of luminance: Area of uniform luminance, L with a width or diameter of at least 15°
A(EXT)
measured from the VDT screen centre.
3.1.3 luminance coefficient (at a surface element, in a given direction, under specified conditions of
illumination)[q , q]: Quotient of the luminance of the surface element in the given direction by the illuminance of the
V
medium. [see IEC (50) 845-04-71].
NOTE — It is expressed per steradian.
3.1.4 luminance factor (at a surface element of a non-self-radiating medium, in a given direction, under specified
conditions of illumination)(b , b): Ratio of the luminance of the surface element in the given direction to that of a
v
perfect reflecting or transmitting diffuser identically illuminated [based on IEC (50) 845-04-69 unit: 1] (unit: 1).
3.1.5 luminance ratio: Ratio between a higher and a lower area-average luminance, in which each luminance in
the ratio is the sum of emitted and reflected luminance components, with one or more components common to both
the numerator and the denominator.
NOTE — To reduce potential confusion, the terms contrast and luminance contrast are avoided in this part of ISO 9241. The
luminance ratios of this part of ISO 9241 do not correspond to the luminance contrast within and between character details of
ISO 9241-3.
3.1.6 negative polarity: Condition in which the foreground luminance L is the highest luminance level of the
F
display, and the background luminance, L is the lowest luminance level of the display.
B
3.1.7 positive polarity: Condition in which the foreground luminance L is the lowest luminance level of the
F
display, and the background luminance, L is the highest luminance level of the display.
B
3.1.8 reflectometer value: Value measured using the test method of this part of ISO 9241 for the diffuse
luminance coefficient, R (an estimate of q) and the specular reflection factor, R (an estimate of b).
D S
NOTE — The measured reflectometer value depends on the geometric characteristics of the test method, on the illuminant,
on the spectral sensitivity of the detector (even when equipped with filters), and on the reference standard used.
[Adapted from CIE 50(845): 1987].
3.1.9 screen tilt angle, a: Angle formed by the intersection of the plane tangent to the centre of the display and
the horizontal plane.
NOTES
1 This is identical to the angle A in 6.1.2 of ISO 9241-3:1992.
2 Figure 1 shows the intended angle.
3 Screen tilt angle is expressed in degrees.
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Key
1 Viewing side
2 Horizontal support surface
Figure 1 — Screen tilt angle
3.1.10 small source of luminance: Area with a diameter of 1° (measured from the screen) of uniform luminance
(L ), to be used in the measurement of specular reflections from screens with diffusing treatments.
A(SML)
3.2 Symbols
3.2.1 Primary symbols
The primary symbols used in this part of ISO 9241 are shown below. See figure 2.
E illuminance, expressed in lux (lx)
2
L luminance, expressed in candela per square metre (cd/m )
LR luminance ratio. (Unit: 1)
R reflectometer value for the diffuse reflection characteristic of the screen, obtained following the procedure
D
below. It is the ratio of diffusely reflected luminance of the screen to its illuminance, under the conditions
-1
specified by clause 7 of this part of ISO 9241 (see 3.1.8). It is expressed per steradian (sr ). The practical
2
unit is candela per square metre per lux [cd/(m � lx)].
reflectometer value for the specular and partially diffuse reflection characteristic of the screen, determined
R
S
following the procedure of clause 7 of this part of ISO 9241. It is the ratio of specular and partially diffuse
reflected luminance of a defined part of the reflected virtual image to the luminance the source of reflections
under the prescribed conditions of measurement (see 3.1.8). (Unit: 1)
3.2.2 Subscripting convention
This part of ISO 9241 uses luminances whose total is made up of contributions from several identifiable
components. Luminance is identified by the symbol L followed by subscripts showing its components. For example
L represents a total luminance composed of contributions from the Foreground emitted luminance, the Specular
FSD
reflected luminance, and the Diffuse reflected luminance. The principal subscripts are:
B the emitted luminance from the display screen Background
F the emitted luminance from the display screen Foreground
D the Diffuse reflected component of a luminance.
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S the Specular reflected component of a luminance.
A the luminance of an Area (whether extended or very small) that is the source of a specular reflection.
(0°) and (15°): the angle at which reflected and/or emitted luminances are measured, or the corresponding diffuse
reflection factor or specular reflection coefficient applied. A measurement angle perpendicular or normal to the
display screen surface is 0°. A measurement angle of 15° to the normal to the screen surface is 15°.
REF: the quantity is a reference value used in compliance calculations. Reference values are not intended to be
reproduced during testing.
STD: the quantity is the calibrated value of a measurement standard.
Subscript modifiers:
(max): the maximum value of a quantity (usually the specular reflection source luminance L ) that will allow the
A(max)
VDT to just meet the requirements of this part of ISO 9241.
(EXT) and (SML): indicate specular reflected luminances and reflection characteristics determined using either an
extended source or a small source of luminance. They are used only to modify the subscript S, as in L ,
S(F, SML, 15°)
the specular reflected luminance of an area of the screen set to the foreground state, from a small source,
measured at 15°.
Composite luminances:
1 L = Luminance of image Foreground + Specular reflection +
FSD
Diffuse reflection
2 L = Luminance of image Background + Specular reflection +
BSD
Diffuse reflection
3 L = Luminance of image Foreground + Diffuse reflection
FD
4 L = Luminance of image Background Diffuse reflection
+
BD
Reflected luminances:
L = Luminance of Specular reflection = R L
S S A
R = Specular reflectometer value (from test method)
S
L = Luminance of an Area causing the specular reflection
A
L = Luminance of Diffusion reflection = R E
D D
R = Diffuse reflectometer value (from test method)
D
E = ambient illuminance
Figure 2 — Screen luminances
3.2.3 Secondary symbols
L , L : The area-average emitted luminances of a patch of pixels in the centre of the screen. The emitted
F B
luminances are to be measured in the lowest and highest luminance levels of the display that are
available for text or its background, under program control.
L , L : Reflected luminances used to decide compliance with this part of ISO 9241 are approximated by a
D S
calculation based on the reflectometer values of the VDT screen and assumed lighting environment
conditions.
LR »�E is the diffuse reflection luminance
DD
where
R is the reflectometer value for the diffuse reflection characteristic of the screen;
D
E is the illuminance incident in the plane of the screen.
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LL »�R is the specular reflected luminance
SS A
where
R is the reflectometer value for the specular and partially diffuse reflection characteristic of the
S
screen;
L is the luminance of a uniform, extended or small luminous source positioned at the specular
A
angle from the point of measurement. The values of L used for compliance with this part of
A
ISO 9241 are specified in clause 6.
Specular reflected luminances and reflection factors are subdivided into those resulting from an extended-source
and a small-source of luminance.
, : specular reflected luminances caused by extended and small sources, respectively.
L L
S(EXT) S(SML)
R , R : specular and partially diffuse reflectometer values of the screen caused by extended and small
S(EXT) S(SML)
sources of luminance, respectively.
LR : luminance ratio of the screen image (foreground and background) with diffuse and specular
BDS/FDS
reflections. It is the ratio between the higher and the lower area-average luminances of the
image, when both specular and diffuse reflected luminances are superimposed on each. See
figure 3. The definition of image luminance ratios is polarity-dependent.
LR positive polarity:
BDS/FDS
LL + + L
BD S
LR ”
BDS/FDS
LL + +L
FD
S
Expanded,
LE + �R+ L �R
BD AS
LR ”
BDS /FDS
LE + �R + L �R
FD AS
(LR ) negative polarity:
FDS/BDS
L L + + L
FD S
LR ”
FDS/BDS
LL + + L
DS
B
Expanded,
LE + �R + L �R
FD AS
LR ”
FDS/BDS
LE + + �R L �R
BD AS
1 in negative polarity
2 in positive polarity
Figure 3 — Image luminance ratio with both specular and diffuse reflections
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LR : specular reflection luminance ratio. It is the ratio between the luminance of an area of the screen
BDS/BD
set to the background state, with a specular reflection and diffuse reflection superimposed, and the
luminance of the same area of the screen without the specular reflection. See figure 4. The
definition is not polarity-dependent.
LL + +L
B
S(B)
D(B)
LR ”
BDS/BD
LL +
B
D(B)
Expanded,
LL ++E �� RR
B D A
S
LR ”
BDS/BD
L +E � R
B D
NOTES
1 Although mathematically the specular reflection luminance ratio is not polarity-dependent, practically and perceptually the
polarity makes a very important difference. In negative polarity, the background is dark, causing much higher specular
reflection luminance ratios. In positive polarity, the background is bright, which dramatically reduces the luminance ratio of
specular reflections. This effect makes positive polarity VDTs far more resistant to the effects of reflections than negative
polarity VDTs with the same highest and lowest luminance levels.
2 In negative polarity the specular reflection is the same polarity as the information displayed on the screen. This leads to
some apparent perceptual competition between the reflection and the useful image. To maintain acceptable image quality, it is
necessary to maintain the image luminance ratio LR substantially greater than that of the specular reflection ratio
FDS/BDS
LR .
BDS/BD
1 In either polarity.
Figure 4 — Luminance ratio of the specular reflection against the screen background
LR : luminance ratio of the screen foreground and background with diffuse reflected luminance only.
FD/BD
It is the ratio between the higher and the lower area-average luminances of the image, when
diffuse reflected luminance is superimposed on each. See figure 5. The maximum acceptable
specular reflection luminance ratio is related to the luminance ratio of the image without
specular reflection, in negative polarity. The definition is polarity-dependent. Only the definition
in negative polarity is used for this part of ISO 9241.
Negative polarity
LL+
F D
LR ≡
FD/BD
LL+
B D
Expanded,
L +ER �
F D
LR
”
FD/BD
L +ER
�
B D
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1 In negative polarity.
Figure 5 — Luminance ratio of the image with diffuse reflection only
4 Guiding principles
The work system is an integrated whole, which includes the visual display work station, environment, task structure,
organizational concerns, and sociological factors. The characteristics of a visual display terminal must be
considered in relation to the other elements of the work system and not as a collection of isolated visual
requirements.
This part of ISO 9241 makes recommendations concerning image quality. The image quality of a visual display work
station should be adequate to meet task demands, and acceptable to the user, in a normal actual work
environment. Design characteristics of the workstation, such as luminance, polarity, screen reflectances and
screen reflection control treatments, influence its ability to maintain its image quality and acceptability when viewed
in varying lighting environments.
NOTE — There are tradeoffs between the design characteristics. For example, positive polarity reduces the contrast of
specular reflections against the screen background. An exclusively positive polarity display possibly requires less reflection
control treatment of the screen surface than an otherwise identical display that uses negative polarity. Design characteristics,
such as reflectance, should be considered as they affect the overall image quality, and not individually.
It is the common responsibility of all parties concerned with the production, installation and use of the VDT, the
workplace and the working room to obtain a good match between the VDT and its environment.
5 Performance objectives
The objective of this part of ISO 9241 is that VDTs be legible and comfortable in use. (See clause 8 for compliance
with this part of ISO 9241.)
6 Requirements
6.1 Image luminance ratio with reflections
The luminance ratio of the image, including superimposed specular and diffuse reflected luminances, shall be equal
to or greater than 3.
In positive polarity, LR ≥ 3 .
BDS/FDS
In negative polarity, LR ≥ 3 .
FDS/BDS
NOTE — These requirements are based on legibility (see annex D, references [10], [11] and [12]).
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6.2 Specular reflection luminance ratio
The luminance ratio LR of a specular reflection against the screen background should be low.
BDS/BD
The perceptibility and acceptability of the specular reflection against the screen background are modified by the
polarity of the screen.
On screens that use positive polarity predominantly, the luminance ratio LR of the specular reflection and the
BDS/BD
bright screen background shall satisfy the relation:
LR 1,25≤
BDS/BD
On screens that use negative polarity (dark background) predominantly, the luminance ratio LR of the
BDS/BD
specular reflection on the dark screen background shall satisfy the relation:
LR
FD/BD
LR 1,2 ≤ +
BDS/BD
15
On screens that use both polarities, the requirements for both positive and negative polarities shall be met.
NOTE — These requirements are based on user acceptance (see annex D, references [10], [11] and [12]).
6.3 Reflection control method and effect on image quality
The VDT shall meet the requirements of relevant clauses of ISO 9241-3 and ISO 9241-8 with its reflection control
treatment, device, or method in place.
6.4 Reference luminous environment
For purposes of determining compliance with this part of ISO 9241, the following luminous environment values shall
be used in the required calculations.
6.4.1 Reference illuminance
The screen angle, a, shall be declared by the supplier of the VDT under test. The reference illuminance E for
REF
compliance determination shall be:
E = 250 + 250 cos(α) lx.
REF
6.4.2 Reference luminance of the source of specular reflections
From the standpoint of establishing the general type of environment suitable for its use, each VDT shall meet the
requirements of this part of ISO 9241 under Class I or Class II or Class III test conditions, choosing the reference
luminance L of the source of specular reflections from table 1.
A(REF)
Table 1 — Test conditions for compliance classes I, II and III
Class Requirement
I L = 200 cd/m² AND L = 2000 cd/m²
A(REF, EXT) A(REF, SML)
II L = 200 cd/m² OR L = 2000 cd/m²
A(REF, SML) A(REF, SML)
III L = 125 cd/m² OR L = 200 cd/m²
A(REF, EXT) A(REF, SML)
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7 Measurements and calculations
This clause provides the method for measurements and calculations related to image quality with reflections, and is
to be used in conjunction with clauses 3 and 6 of this part of ISO 9241.
Regardless of the test requirements for the intended class of compliance, testing of each VDT screen should be
conducted using both the extended and small sources of luminance.
7.1 General
See figure 6 for overall test equipment setup.
a) At 0° (perpendicular to the VDT screen), determine the diffuse reflectometer factor R (approximating the diffuse
D
reflection coefficient q).
b) At 15° incidence to the VDT screen:
— Measure the foreground and background emitted luminances L and L (in both polarities if appropriate).
F B
— Determine the small-source and/or extended-source specular reflectometer value(s) R (approximating the
S
specular reflection factor, b).
c) Determine the VDT's compliance with the requirements of this part of ISO 9241:
— Calculate the luminance ratios defined in clause 3 of this part of ISO 9241, using the measured screen
luminances, the diffuse and specular reflectometer factors, and the reference illuminance and luminance(s) of
6.4.
— Determine if compliance with the requirements of clause 6 is achieved.
Key
1 Spot photometer
2 Extended luminance source
3 VDT under test
Figure 6 — Basic apparatus arrangement
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7.2 Apparatus
The following equipment is required to complete this measurement procedure:
7.2.1 Spot photometer
See figure 7 for terms used in setting photometer requirements.
— For measurements using extended specular reflection sources, the field of view (FOV) should be 1° to 2° and
the working distance should exceed 500 mm.
NOTE 1 The important factor in the measurement is that the FOV and working distance jointly determine a spot size on the
screen that is both smaller than the size of the luminous patch measured and sufficiently large that aperture factors (from the
screen structure on the order of 0,03°) are minimal.
— For measurements using the small source of specular reflections, a photometer with a round field of view of 0,3°
or less shall be used, and the working distance shall be 500 mm – 50 mm. The spot photometer, at working
distance of 500 mm should have an acceptance cone of < 1. The acceptance cone shall be specified.
The values of the acceptance cone, the field of view and the working distance shall be reported.
NOTE 2 The magnification of the overall (source-screen-photometer) optical system is critical to the relationship of the virtual
image of the small source to the photometer field of view. The field of view must be smaller than the virtual image. The data
correlating user responses to reflections and small-source measurements are valid for the specified measurement geometry
only.
Key
1 Photometer 4 Acceptance cone: Angle formed by the entrance pupil of
the instrument and the working distance
2 Photosensitive element 5 Specimen
3 Field of view: Angular extent of the considered object 6 Working distance range: Distance between the
...
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