EN ISO 9241-306:2008

SLOVENSKI STANDARD
01-januar-2009
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SROMDHOHNWURQVNLKVOLNRYQLK]DVORQRY,62
Ergonomics of human-system interaction - Part 306: Field assessment methods for
electronic visual displays (ISO 9241-306:2008)
Ergonomie der Mensch-System-Interaktion - Teil 306: Vor-Ort-Bewertungsverfahren für
elektronische optische Anzeigen (ISO 9241-306:2008)
Ergonomie de l'interaction homme/systeme - Partie 306: Méthodes d'appréciation du
champ pour écrans visuels électroniques (ISO 9241-306:2008)
Ta slovenski standard je istoveten z: EN ISO 9241-306:2008
ICS:
13.180 Ergonomija Ergonomics
35.180 Terminalska in druga IT Terminal and other
periferna oprema IT peripheral equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 9241-306
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2008
ICS 13.180; 35.180
English Version
Ergonomics of human-system interaction - Part 306: Field
assessment methods for electronic visual displays (ISO 9241-
306:2008)
Ergonomie de l'interaction homme-système - Partie 306: Ergonomie der Mensch-System-Interaktion - Teil 306: Vor-
Méthodes d'appréciation sur le terrain des écrans de Ort-Bewertungsverfahren für elektronische optische
visualisation électroniques (ISO 9241-306:2008) Anzeigen (ISO 9241-306:2008)
This European Standard was approved by CEN on 12 April 2008.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
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This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
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© 2008 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9241-306:2008: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
This document (EN ISO 9241-306:2008) has been prepared by Technical Committee ISO/TC 159
"Ergonomics" in collaboration with Technical Committee CEN/TC 122 "Ergonomics", the secretariat of which
is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of an identical
text or by endorsement, at the latest by May 2009, and conflicting national standards shall be withdrawn at the
latest by May 2009.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 9241-306:2008 has been approved by CEN as a EN ISO 9241-306:2008 without any
modification.
INTERNATIONAL ISO
STANDARD 9241-306
First edition
2008-11-15
Ergonomics of human-system
interaction —
Part 306:
Field assessment methods for electronic
visual displays
Ergonomie de l'interaction homme-système —
Partie 306: Méthodes d'appréciation sur le terrain des écrans de
visualisation électroniques
Reference number
ISO 9241-306:2008(E)
©
ISO 2008
ISO 9241-306:2008(E)
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ii © ISO 2008 – All rights reserved

ISO 9241-306:2008(E)
Contents Page
Foreword. iv
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Preparation for assessment . 1
4.1 Cathode ray tube (CRT) displays . 1
4.2 Liquid crystal displays (LCD) . 2
5 Assessment methods. 3
5.1 Viewing conditions . 3
5.2 Luminance . 5
5.3 Special physical environments . 7
5.4 Visual artefacts . 8
5.5 Legibility and readability. 11
5.6 Legibility of information coding. 13
5.7 Legibility of graphics. 14
5.8 Fidelity . 15
6 Other considerations. 16
6.1 Isotropic surface. 16
6.2 Anisotropic surfaces . 16
6.3 Viewing angle range . 16
6.4 Adjustability . 16
6.5 Controllability. 17
6.6 Luminous environment . 17
Annex A (informative) Overview of the ISO 9241 series. 18
Annex B (informative) Influences on ergonomics parameters of visual displays. 22
Annex C (informative) Unwanted reflections. 25
Annex D (informative) Display output linearization and evaluation of achromatic ISO/IEC test
chart output for eight different ambient light reflections at office work places. 28
Bibliography . 45

ISO 9241-306:2008(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. 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.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 9241-306 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 4: Keyboard requirements
⎯ Part 5: Workstation layout and postural requirements
⎯ Part 6: Guidance on the work environment
⎯ Part 9: Requirements for non-keyboard input devices
⎯ Part 11: Guidance on usability
⎯ Part 12: Presentation of information
⎯ Part 13: User guidance
⎯ Part 14: Menu dialogues
⎯ Part 15: Command dialogues
⎯ Part 16: Direct manipulation dialogues
⎯ Part 17: Form filling dialogues
iv © ISO 2008 – All rights reserved

ISO 9241-306:2008(E)
ISO 9241 also consists of the following parts, under the general title Ergonomics of human-system interaction:
⎯ Part 20: Accessibility guidelines for information/communication technology (ICT) equipment and services
⎯ Part 110: Dialogue principles
⎯ Part 151: Guidance on World Wide Web user interfaces
⎯ Part 171: Guidance on software accessibility
⎯ Part 300: Introduction to electronic visual display requirements
⎯ Part 302: Terminology for electronic visual displays
⎯ Part 303: Requirements for electronic visual displays
⎯ Part 304: User performance test methods for electronic visual displays
⎯ Part 305: Optical laboratory test methods for electronic visual displays
⎯ Part 306: Field assessment methods for electronic visual displays
⎯ Part 307: Analysis and compliance test methods for electronic visual displays
⎯ Part 308: Surface-conduction electron-emitter displays (SED) [Technical Report]
⎯ Part 309: Organic light-emitting diode (OLED) displays [Technical Report]
⎯ Part 400: Principles and requirements for physical input devices
⎯ Part 410: Design criteria for physical input devices
⎯ Part 920: Guidance on tactile and haptic interactions
For the other parts under preparation, see Annex A.
ISO 9241-306:2008(E)
Introduction
This part of ISO 9241 is one of a group of standards in the ISO 9241 series that establish requirements for the
ergonomic design of electronic visual displays. At the same time, this “300” subseries replaces either partially
or fully certain previously published parts of ISO 9241 as well as several other International Standards (see
the Forewords of the respective parts for the details).
⎯ An introduction to the subseries is given by ISO 9241-300.
⎯ Terms and definitions related to electronic visual displays have been transferred to, and collected in,
ISO 9241-302.
⎯ While the areas previously covered in ISO 9241 and by ISO 13406 remain essentially unchanged, test
methods and requirements have been updated to account for advances in science and technology.
⎯ All generic ergonomic requirements have been incorporated into ISO 9241-303.
⎯ The application of those requirements to different display technologies, application areas and
environmental conditions — including test methods and pass/fail criteria — are specified in ISO 9241-307.
⎯ Methods for performing formal display measurements to determine display characteristics and verify
technical specifications (tests that can be very costly and time-consuming and that are normally
performed under rigorous test conditions with a new device) are given in ISO 9241-305 and
ISO 9241-307.
⎯ In addition, guidance on the design of SED (surface-conduction electron-emitter displays) and OLED
(organic light-emitting diode) displays is given in ISO/TR 9241-308 and ISO/TR 9241-309.
The overall modular structure of the subseries will facilitate its revision and amendment, as ongoing
technological development enables new forms of display interaction.
This part of ISO 9241 is concerned with ergonomic workplace assessment and is aimed at providing a means
of assessing whether or not the visual ergonomic requirements specified in ISO 9241-303 are satisfied within
a specified task setting. The intention is not necessarily to produce a perfect display with optimum visual
characteristics, but rather to ensure that the needed qualities to perform the visual task satisfactorily are
indeed present.
During the lifetime of a display, the context in which it is used can often vary; “ageing” normally takes place as
the display is used and, as a result, the performance of the display may be reduced over time. The lighting
conditions under which a display is used often also vary.
In actual VDT workstation use, the main ergonomic concerns are the visual task being performed and the
input devices being used to accomplish the task.
There are several factors that make the performance of a visual task using a VDT different from that in many
other non-VDT or paper tasks. These factors are related to the positioning of the various elements needed for
performing the visual task.
The ergonomic goal is to be able to read the information on the display comfortably, easily, accurately and
quickly (where necessary) — as when a paper “hardcopy” placed on the work desk is read.
One consideration is what might be called the positional sensitivity of the screen. If positioned poorly, displays
are susceptible to external light sources: these can be reflected back to the viewer and can contribute to
reduced legibility of the information on the screen. In more compelling environments, these light sources can
give rise to glare. They can come from either natural light from windows or from artificial lighting systems such
as overhead mounted luminaries in offices.
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ISO 9241-306:2008(E)
Given the size and dimensions of most displays, a display is typically oriented in a vertical rather than
horizontal position. This orientation and position of the information to be read is considerably different than
that when a book or paper placed on the desk is read. The line of sight from the eye to the visual task is raised
up to 45°, giving rise to a quite different visual background, often with a varying luminous background arising
from walls and other objects in the environment. These factors can affect the working posture of a user trying
to compensate between the line of sight angle to the display needed to be maintained and the distance to the
visual task.
These and other considerations demonstrate that the positioning of a display is much more important than the
mere positioning of paper or other hardcopy reading materials. They gives rise to the need to be able to adjust
the display for orientation and height and to have the flexibility to set up the workstation equipment so that the
needs of a specific user can be realized. The combination of display, lighting environment and workstation
equipment are the basics for an ergonomically well-designed workplace.
Unlike most visual task materials, displays are intended to be used for several years. Many other kinds of
work materials are used only once or a few times, or are renewed or refreshed when visibility is too low or
possibly too uncertain (e.g. safety instructions or warnings), or else simply remain unchanged over time.
The display assessment methods presented in this part of ISO 9241 do not, in most cases, require expensive
measuring equipment and will in general be able to be carried out easily in a working field environment. In
conducting these assessments, it ought to be possible to determine whether a problem is related to
a) the display itself (or the display in combination with the graphic adapter),
b) the application software, or
c) physical environmental conditions.
In cases involving a), the display, it is beneficial that the workstation set-up be reviewed to determine whether
it meets the supplier’s recommendations; if it does not, another assessment will need to be performed to
determine how it can be made to meet them. In cases involving b), the application software, it might be
necessary to contact the software developers of the application product in order to ascertain possible
corrective action. In cases involving c), conditions in the physical environment, simple re-orientations or the
repositioning of the workstation and/or display can be a satisfactory solution; whereas, in more complex
situations, arrangements might need to be made with the relevant interested parties in order to ascertain
appropriate actions and their feasibility. For details, see Annex B.
ISO 9241 was originally developed as a 17-part International Standard on the ergonomics requirements for
office work with visual display terminals. As part of the standards review process, a major restructuring of
ISO 9241 was agreed to broaden its scope, to incorporate other relevant standards and to make it more
usable. The general title of the revised ISO 9241, Ergonomics of human-system interaction, reflects these
changes and aligns the standard with the overall title and scope of Technical Committee ISO/TC 159,
Ergonomics, Subcommittee SC 4, Ergonomics of human-system interaction. The revised multipart standard is
structured as a series of standards numbered in the “hundreds”: the 100 series deals with software interfaces,
the 200 series with human centred design, the 300 series with visual displays, the 400 series with physical
input devices and so on.
See Annex A for an overview of the entire ISO 9241 series.

INTERNATIONAL STANDARD ISO 9241-306:2008(E)

Ergonomics of human-system interaction —
Part 306:
Field assessment methods for electronic visual displays
1 Scope
This part of ISO 9241 establishes optical, geometrical and visual inspection methods for the assessment of a
display in various contexts of use according to ISO 9241-303.
2 Normative references
The following referenced documents are indispensable for the application 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 9241-303:2008, Ergonomics of human-system interaction — Part 303: Requirements for electronic visual
displays
ISO 9241-305, 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
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9241-302 apply.
4 Preparation for assessment
4.1 Cathode ray tube (CRT) displays
4.1.1 Display warm-up
Allow sufficient time (at least 20 min) for the display luminance to stabilize.
4.1.2 Degaussing
If a monitor has a built-in degaussing device, activate it.
ISO 9241-306:2008(E)
4.1.3 Cleaning
Ensure that the front glass of the display is clean; otherwise, clean it according to the manufacturer’s
instructions.
4.1.4 Contrast and brightness control settings
Adapt display contrast and brightness using contrast and brightness screen controllers according to the
environmental lighting conditions, as follows:
⎯ use a pattern that contains areas of different grey scale values from white to black;
⎯ set both contrast and brightness to maximum (100 %);
⎯ in a dark environment, reduce brightness until the darkest pattern area is displayed completely black —
the difference between the darkest and the next lighter area should be distinguishable;
⎯ set the contrast so that the brightness of the white area is at the maximum while the difference between
the white and the next darker area is distinguishable;
⎯ in a non-dark environment, set the brightness to a value where all grey levels are distinguishable.
4.1.5 Image size
Use factory or default setting if available. Otherwise, adjust to a specified size.
4.2 Liquid crystal displays (LCD)
The flat panel display shall be physically prepared for assessment.
4.2.1 Display warm-up
Allow sufficient time (at least 20 min) for the display luminance to stabilize. When indicated by the
manufacturer, it shall be warmed up for the specified time.
4.2.2 Cleaning
Ensure that the display is clean; otherwise, clean it according to the manufacturer’s instructions.
4.2.3 Contrast and brightness control settings
Adapt display brightness and contrast (if controllers are available) according to the environmental lighting
conditions, as follows:
⎯ use a pattern that contains areas of different grey scale values from white to black;
⎯ set both contrast and brightness to maximum (100 %);
⎯ set contrast to a value where all grey levels are distinguishable;
⎯ display the content of a typical application and set brightness to a level appropriate to the lighting
conditions.
2 © ISO 2008 – All rights reserved

ISO 9241-306:2008(E)
4.2.4 Resolution
Use the factory-recommended (physical) resolution. Changing this native resolution to another can cause a
degradation of the display image quality and character presentation, due to imperfect pixel interpolation
(see Figure 1).
physical reduced
Figure 1 — Comparison of letters displayed with physical and reduced resolutions
5 Assessment methods
5.1 Viewing conditions
5.1.1 Design viewing distance
The optimum distance between the visual display and the user's eyes depends on various factors, and in
particular character legibility (see Table 1) and the possibility of viewing a full application without head
movement (see Table 2). The design viewing distance, i.e. the distance specified by the manufacturer of the
display is set to W 300 mm (see ISO 9241-303). The optimum viewing distance for office work in a seated
position is 600 mm. However, individual users tend to prefer settings between 400 mm and 750 mm. Viewing
distances in this range for most people require character heights that subtend between 20′ to 22′ of arc (see
ISO 9241-303).
Check whether the display is used within the specified viewing distance, D. Measure the distance from the
user's eyes to the centre of the screen with a ruler. For office work, the normal range is 400 mm to 750 mm: if
the chosen distance is outside of this range, verify that there is not an underlying problem, such as bad image
quality, incorrect font size or an uncorrected vision problem.

ISO 9241-306:2008(E)
If the visual task requires that the entire application, i.e. its page or line width, is viewed at a glance, i.e.
without head movements, the minimum viewing distances from Table 2 are recommended. They result from
the maximum horizontal viewing angle of ± 15° with respect to the normal on the screen surface, which allows
such viewing at a glance and depends on screen size. Figure 2 shows the relation between viewing angle,
application width and viewing distance.
Table 1 — Maximum and optimum viewing distances for character legibility
Maximum viewing distance for some Viewing distance of generally accepted
Character height
users legibility
mm
cm cm
1,2 41 20
2 69 33
3 103 49
4 138 65
4,6 158 75
NOTE 1 The maximum viewing distance is based on character height of 10′ of arc and is usable only by a small number of users.
Generally accepted legibility, i.e. one that is well accepted by most users, is calculated based on 21′ of arc. The optimum character
height for task performance is a compromise between the legibility goal and the goal of “surveying at a glance” — presenting all
information related to the same context on the same screen.
NOTE 2 The simplified rule of thumb for character legibility is: for optimum legibility, viewing distance ≈ 165 × character height:
⎯ acceptable range ≈ ± 30 % for most users;
⎯ acceptable range ≈ ± 100 % for some users.

Table 2 — The smallest viewing distance at which the full application width can be used without need
for head movement
Width of the application (or page or line) Minimum viewing distance in order to avoid head movement
mm cm
215 40
250 47
300 56
350 65
400 75
NOTE 1 The relationship is based on the ± 15° requirement illustrated by Figure 2.
NOTE 2 In the field, it can be convenient to use the following approximation as a rule of thumb: viewing distance W 1,9 × application
width.
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ISO 9241-306:2008(E)
Key
1 screen width
2 viewing angle (± 15°)
3 viewing distance
4 viewing location
Figure 2 — Viewing distance and viewing angle

5.1.2 Design viewing direction
If the display is a flat panel, check that it is used for the specified viewing direction class according to
ISO 9241-303 and ISO 9241-307.
5.1.3 Gaze and head tilt angles
Verify that the work station and the visual display allow the user to view the screen with a gaze angle from 0°
to 45° and a head tilt angle from 0° to 20°, using a device for measuring angles such as protractor or
goniometer.
5.1.4 Virtual images
See ISO 9241-303:2008, Annex E.
5.2 Luminance
5.2.1 Illuminance
Measure the screen illuminance using a lux meter. Place the lux meter’s sensor directly in the centre of the
screen at the same tilt angle as applied by the user. Check that no shadows are falling onto the sensor.
Verify that the measured illuminance corresponds to the value specified by the supplier.

ISO 9241-306:2008(E)
5.2.2 Display luminance
Measure the area luminance with a luminance meter: first, for white pattern on black background and, second,
for black pattern on white background. Place the meter perpendicular to the display surface on the target. The
target area shall be at least 100 % larger than the measurement area of the luminance meter.
For CRT, the luminance meter should be placed at measurement locations as shown in Figure 3. The pattern
is the following:
⎯ at the centre;
⎯ at the locations on the diagonals that are 10 % of the diagonal length from the corners of the addressable
area of the display.
Figure 3 — Measurement locations — CRT

Verify that the measured luminance values are in accordance with ISO 9241-307.
For LCD, the measurement locations should be as shown in Figure 4. Determine the lowest and highest
luminance.
Verify that the measured luminance values are in accordance with ISO 9241-307.

6 © ISO 2008 – All rights reserved

ISO 9241-306:2008(E)
Key
H visible display height
view
W visible display width
view
Figure 4 — Measurement locations — LCD

5.2.3 Luminance balance and glare
Measure the luminance of the display (e.g. full screen white), of a frequently viewed task area (e.g. a
document on the desk) and of a selected surround (e.g. a room wall). Calculate the luminance ratio between
the screen and the frequently viewed area. Perform the same calculation for the luminance ratio between the
screen and selected surround. Verify that the ratios are in accordance with the value range specified in
ISO 9241-303.
A possible method of controlling the avoidance of glare is to check whether the surface of the housing is matte
or glossy. Glossy surfaces may produce glare; the gloss value can be measured with a gloss meter or gloss
reference samples.
5.2.4 Luminance adjustment
Verify that the luminance of the display and the contrast between characters and character background on the
display are adjustable by the user to the ambient environmental conditions of the workplace.
5.3 Special physical environments
5.3.1 Vibration
See ISO 9241-303:2008, 5.3.2.
5.3.2 Wind and rain
See ISO 9241-303:2008, 5.3.3.
5.3.3 Excessive temperatures
See ISO 9241-303:2008, 5.3.4.
ISO 9241-306:2008(E)
5.4 Visual artefacts
5.4.1 Luminance non-uniformity
Estimate the luminance non-uniformity by sequentially viewing different areas on the screen to determine the
degree of non-uniformity. If it is determined that a noticeable amount of luminance non-uniformity is present,
then the measurement of luminance with a luminance meter is recommended.
The measurement locations are the positions on the screen with the lowest and highest luminance (see 5.2.2).
Determine the luminance non-uniform ratio using Equation (1):
⎛⎞
LL−
max min
non-uniformity= 100 % (1)
⎜⎟
L
⎝⎠max
Verify that the luminance uniformity value is according to ISO 9241-307.
5.4.2 Colour non-uniformity
Display the full screen with only one colour and estimate the colour non-uniformity by sequentially viewing
different areas on the screen. Repeat with different colours.
The subjective impression of colour is not only determined by the colour itself (chromaticity) but also by the
luminance. For applications requiring exact colour distinction, use a colorimeter or a spectrophotometer. For
further details, see ISO 9241-305.
5.4.3 Contrast non-uniformity
Calculate the contrast non-uniformity from the values measured in 5.2.2 using Equation (2):
⎛⎞
CC−
max min
non-uniformity= 100 % (2)
⎜⎟
C
⎝⎠max
5.4.4 Geometric distortions
Disturbing changes of character form or character location due to image stability or geometry faults should not
occur. Such geometrical faults can be ascertained, for example, by placing a rectangular sheet of paper on
the horizontal or vertical lines in the intended area of the display.
Most of these faults can be corrected using the screen display controls.
5.4.5 Pixel faults
5.4.5.1 Pixel/subpixel stuck on
These pixels/subpixels will always appear as bright on a black background. Use a black screen to observe.
5.4.5.2 Pixel/subpixel stuck dim
These pixels/subpixels can appear as grey, independent of white or black background. To observe, first use a
white and then a black screen.

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ISO 9241-306:2008(E)
5.4.5.3 Pixel/subpixel stuck off
These pixels/subpixels always appear as dark on a white screen. Use a white screen to observe.
NOTE For a complete analysis, refer to Reference [7]. To determine the pixel fault class, see ISO 9241-307.
5.4.6 Temporal instability (flicker)
For CRT screens, flicker-free perception mainly depends on the interplay between the following factors:
⎯ technical factors such as image refresh rate, image formation, resolution, phosphor persistence, average
display luminance and the size of the display area;
⎯ the individual operator’s visual capabilities.
For CRT screens in positive polarity, use Figure 5 (which shows relationship between refresh rate, resolution
and horizontal frequency) to determine the combinations needed to achieve a flicker-free screen. The
recommended refresh rate is 100 Hz.
If the refresh rate is set to a value lower than 85 Hz, change it to a higher one if technically possible (depends
on line frequencies of the monitor and properties of the graphic card).

Key
X refresh rate, Hz
Y horizontal frequency, kHz
Figure 5 — Correlation between refresh rate, horizontal frequency and resolution
ISO 9241-306:2008(E)
The higher the needed refresh rate and resolution, the higher the horizontal frequency has to be, e.g. a
horizontal frequency of 70 kHz is required in order to display image with refresh rate of 85 Hz and a resolution
of 1024 × 768.
An alternative method for determining the presence of flicker is the following.
a) Adjust the display to present a white background (positive polarity).
b) Adjust the brightness and the contrast to the maximum.
c) Focus on a point about 30° to the left or to the right of the display; ensure that the display can be seen in
the peripheral part of vision.
d) If the screen is not flicker free, flicker will be seen in the peripheral part of vision. In this case, check the
refresh rate setting and adjust it to a higher level, if possible.
For display technologies such as LCD, electrical luminescence and plasma displays, other technical factors
can be decisive for a flicker-free perception.
5.4.7 Spatial instability (jitter)
Jitter can be caused by either the display itself (internal) or by external electromagnetic fields (e.g. power line
of railway, transformer, external power supply of IT equipment).
For LCD technology, jitter cannot be caused by external electromagnetic fields.
A strong jitter can be simply observed by the user without a measurement device. Jitter measurements can be
performed using a magnifying glass with a built-in scale.
For measurement methods, see ISO 9241-305.
5.4.8 Moiré effects
Moiré effects can be detected by visual inspection or appropriate monitor test programs.
Some visual displays have a built-in correction function that should be used to eliminate Moiré effects.
5.4.9 Other instabilities
Other instabilities such as swim, drift, crosstalk or shadows on objects or characters can be detected by visual
inspection. See ISO 9241-303.
5.4.10 Unwanted reflections
Disturbing reflections can be determined by visual inspection. Annex C gives guidelines for avoiding
reflections.
Displays are divided according to their anti-reflection capabilities, separated, for positive and negative polarity,
into three classes, see Table 3.
Table 3 — Reflection class of screen
Reflection class Environment
I Suitable for general office use
II Suitable for most, but not all office environments
III Requiring a specially controlled luminous environment
10 © ISO 2008 – All rights reserved

ISO 9241-306:2008(E)
To determine if the display is suitable for the intended use in the given environment, check the data sheet or
ask the vendor for reflection class.
For a typical office environment, positive polarity is recommended because unavoidable reflections have a
less disturbing effect compared to negative polarity.
5.4.11 Unintended depth effects
Review the application for the presence of spectrally extreme colours in accordance with Table 4.
Table 4 — Spectrally extreme colours
Image background Requirement/recommendation Consideration/reference
Positive polarity,
Preferred for most tasks See ISO 9241-303.
achromatic
Depth of field of the eye.
Avoid blue on red as primary
Positive polarity,
colour
False, unwanted (chromo)stereopsis.
chromatic
Use black or dark grey foreground Colour identification.
Poor legibility. For text presentation,
Avoid blue as primary colour
difficult to meet contrast requirements.
Negative polarity,
achromatic
About 8 % of users have reduced red-
Avoid red as primary colour
green discrimination.
Depth of field of the eye.
Negative polarity, Avoid red on blue as primary
chromatic colour
False, unwanted (chromo)stereopsis

Spectrally extreme colours (extreme blue, extreme red) that produce depth effects (chromostereopsis) shall
not be presented for images to be continuously viewed or read.
5.5 Legibility and readability
5.5.1 Luminance contrast
5.5.1.1 CRT — Inner contrast on characters or objects having non-discrete, non-uniform small area
luminance distribution
This assessment can only be made using a scanning or imaging photometer with appropriate aperture. For
further details, see ISO 9241-305.
5.5.1.2 LCD — Area luminance contrast of flat panel displays
Measure the area luminance with a luminance meter. Follow the procedure as specified in 5.2.2.
5.5.2 Image polarity
See ISO 9241-303:2008, 5.5.3.
ISO 9241-306:2008(E)
5.5.3 Character height
5.5.3.1 Character height measured with comparator foil — LCD and CRT
Use a plastic foil with targets of different known height or a magnifier with a scale. Place the foil/magnifier on
the screen. Compare the targets on the foil with the character height on the screen or measure the character
height with a magnifier. Calculate the character height as a subtended visual angle, α, in minutes of arc, using
Equation (3):
⎛⎞hh3438×
TT
α=×60 2 arctan ≈ (3)
⎜⎟
2×DD
⎝⎠
where
h is the target height, in millimetres;
T
D is the viewing distance, in millimetres.
5.5.3.2 Character size determined from pixel count and screen height
Count the number of pixels, n, in the height of the character.
Use a pixel-oriented character program, often included in operating systems (see Figure 6).

Figure 6 — Zoomed characters within a grid
Calculate the character height as a subtended visual angle, α, in minutes of arc, using Equation (4):
⎛⎞
ns××p 3438 n×sp
α=×60 2 arctan ≈ (4)
⎜⎟
2×DD
⎝⎠
where
D is the viewing distance, in millimetres;
n is the number of pixels in the height of the character;
p is the screen height, in pixels;
s is the screen height, in millimetres.
The screen size (height and width) is defined by the manufacturer in the user’s manual or technical
specification (such as a data sheet). For CRT displays, ensure that the screen size used is the same as that
specified by the manufacturer; if not, change the screen size accordingly.
12 © ISO 2008 – All rights reserved

ISO 9241-306:2008(E)
5.5.3.3 Screen height
For CRT, place a ruler on the screen and measure the screen height. Ensure that the eyes are perpendicular
to the screen while measuring. Repeat the measurement and calculate the average value of the screen
height, s.
5.5.4 Text size constancy
Perform a visual inspection.
5.5.5 Character stroke width
Use a comparator foil or a magnifier with a scale to determine the character stroke width. Place the
foil/magnifier on the character on the screen. Ensure that the eyes are perpendicular to the screen while
measuring.
5.5.6 Character width-to-height ratio
Use a comparator foil or a magnifier with a scale to determine the character width and height. Calculate the
ratio.
As an alternate procedure, use the method specified in 5.5.3.2 for determining the character width and height.
Calculate the ratio.
5.5.7 Character format
Count the number of pixels in the height and width of the selected character. Use the procedure specified in
5.5.3.2.
5.5.8 Between-character spacing
Use a comparator foil with a scale to measure the spacing between characters. For further consideration, refer
to ISO 9241-303:2008, 5.5.9.
As an alternate procedure, use the method specified in 5.5.3.2 for determining the space between two
characters. Count the space in pixels.
5.5.9 Between-word spacing
Use a comparator foil with a scale to measure the spacing between words.
As an alternate procedure, use the method described in 5.5.3.2 for determining the space between two words.
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