ISO/TR 20278:2015
(Main)Unwanted reflections from the active and inactive areas of display surfaces visible during use
Unwanted reflections from the active and inactive areas of display surfaces visible during use
ISO/TR 20278:2015 provides users a summary of the existing knowledge about ergonomics requirements for unwanted reflections on electronic displays. The document furthermore provides some guidance on specification of unwanted reflections. NOTE ISO 9241 contains normative requirements related to unwanted reflections. It is possible that the information contained in this Technical Report will be used for a future update of ISO 9241.
Réflexions non désirées des zones actives et inactives des surfaces de l'écran visibles durant l'utilisation
General Information
Standards Content (Sample)
TECHNICAL ISO/TR
REPORT 20278
First edition
2015-12-01
Unwanted reflections from the active
and inactive areas of display surfaces
visible during use
Réflexions non désirées des zones actives et inactives des surfaces de
l’écran visibles durant l’utilisation
Reference number
ISO/TR 20278:2015(E)
©
ISO 2015
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ISO/TR 20278:2015(E)
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ISO/TR 20278:2015(E)
Contents Page
Foreword .v
1 Scope . 1
2 Terms and definitions . 1
3 Unwanted reflections within the context of the ISO 9241-3xx series .2
3.1 Glare and unwanted reflections . 2
3.2 Direct glare in the context of the ISO 9241-3xx standards series . 2
3.3 Glare by reflection . 3
4 Visual discomfort and glare while using computer displays . 3
4.1 Asthenopia . 3
5 Unwanted reflections from displays . 3
5.1 General . 3
5.2 Glare and unwanted reflections on screens in the ISO 9241-3xx series . 4
6 Pertinent regulations regarding glare and unwanted reflections .4
6.1 European Directive 90-270 — On the minimum safety and health requirements
for work with display screen equipment . 4
6.2 The meaning of disturbing glare within the ISO 9241-3xx series . 4
6.2.1 General. 4
6.2.2 CIE definitions of discomfort glare and disability glare . 4
6.2.3 Unwanted reflections as currently specified and limited in ISO 9241-303,
9241-305 and 9241-307 for the active area of displays (screens) . 5
6.3 Interaction between specular, diffuse and haze reflection components . 6
6.3.1 General. 6
6.3.2 Recognition of the interaction of unwanted reflection components in the
ISO 9241-3xx series . 6
7 Luminance balance . 6
8 Glare and the ambient illumination in the office-working environment .6
8.1 Ambient illuminance . 6
8.2 Arrangement of the computer work area . 7
8.3 Surface finishes (reflectivity) . 7
8.3.1 General. 7
8.3.2 Conversion of specular gloss values to specular reflectance values . 8
9 Literature review of research regarding unwanted reflections from the bezel,
screen housing, or other inactive areas of the display visible during use .8
9.1 General . 8
9.2 Bezel gloss . 8
9.2.1 Howarth and Hodder, 2004 . 8
9.2.2 Béland and Andrén . 8
9.2.3 Howarth and Hodder, 2013 . 8
9.3 Bezel reflectance . 9
9.3.1 General. 9
9.3.2 Hunter, et al. . 9
9.3.3 Soderston, et al. . 9
9.3.4 Béland and Andrén .10
9.3.5 Howarth and Hodder .11
9.3.6 Conclusions from the literature regarding bezel gloss and reflectance .11
10 A review of the literature regarding eyestrain due to vergence and accommodative
demands of glare reflections .11
10.1 Accommodative stress .11
10.2 Vergence stress .12
11 Summary and conclusions .12
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ISO/TR 20278:2015(E)
Bibliography .14
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ISO/TR 20278:2015(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
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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 documents 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 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. 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 www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT), see the following URL: Foreword — Supplementary information.
The committee responsible for this document is ISO/TC 159, Ergonomics, Subcommittee SC 4, Ergonomics
of human-system interaction.
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TECHNICAL REPORT ISO/TR 20278:2015(E)
Unwanted reflections from the active and inactive areas of
display surfaces visible during use
1 Scope
This Technical Report provides users a summary of the existing knowledge about ergonomics
requirements for unwanted reflections on electronic displays. The document furthermore provides
some guidance on specification of unwanted reflections.
NOTE ISO 9241 contains normative requirements related to unwanted reflections. It is possible that the
information contained in this Technical Report will be used for a future update of ISO 9241.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
asthenopia
weakness or tiring of the eyes accompanied by pain, headache, and dim vision
Note 1 to entry: Symptoms include pain in or around the eyes; headache, usually aggravated by using the eyes for
close work; fatigue; vertigo; and reflex symptoms such as nausea, twitching of facial muscles, or migraine.
[SOURCE: Taber’s Medical Dictionary]
2.2
disability glare
glare that impairs the vision of objects without necessarily causing discomfort
2.3
direct glare
glare caused by self-luminous objects located in the visual field, especially near the line of sight
2.4
discomfort glare
glare that causes discomfort without necessarily impairing the vision of objects
2.5
glare
condition of vision in which there is discomfort or a reduction in the ability to see details or objects,
caused by an unsuitable distribution or range of luminance, or by extreme contrasts
2.6
glare by reflection
glare produced by reflections, particularly when the reflected images appear in the same or nearly the
same direction as the object viewed
2.7
gloss (of a surface)
mode of appearance by which reflected highlights of light sources of objects are perceived as
superimposed on the surface due to the directionally selective properties of that surface
2.8
glossmeter
instrument for measuring the various photometric properties of a surface giving rise to gloss
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ISO/TR 20278:2015(E)
2.9
reflectometer
instrument for measuring quantities pertaining to reflection
2.10
specular gloss
ratio of the luminous flux reflected from an object in the specular direction for a specified source
and receptor angle to the luminous flux reflected from glass with a refractive index of 1,567 in the
specular direction
2.11
veiling glare (imaging)
light, reflected from an imaging medium, that has not been modulated by the means used to
produce the image
3 Unwanted reflections within the context of the ISO 9241-3xx series
3.1 Glare and unwanted reflections
At various places in the ISO 9241-3xx series, we specifically adopt the CIE definition of glare, which
includes both discomfort glare and disability glare. We note that the CIE defines discomfort glare
verbally as:
[11]
“glare which causes discomfort without necessarily impairing the vision of objects”,
and disability glare as
[13]
“glare that impairs vision”.
Glare is commonly classed as direct glare, in which the eye is directly illuminated by some object, such
as a display, a luminaire or the sun, and indirect glare, in which the eye is illuminated by light reflected
from a surface such as that of a display screen.
3.2 Direct glare in the context of the ISO 9241-3xx standards series
ISO 9241-6 discusses two types of glare in the context of office working environments. Direct glare is
described thusly:
“Direct glare from daylight can typically be caused by a direct view of the sun or clouds and by
[2]
their reflections on adjacent buildings.”,
and
“Direct glare from artificial lighting can be caused by luminaires or illuminated room surfaces with
high luminance”.
Clearly, direct glare is seen to be associated with reflections as well as luminance sources directly in
the user’s line of sight.
In general, room lighting as a source of direct glare has been studied extensively and appropriate designs
are well specified. However it is important to note that the recent introduction of new technologies
such as luminaires composed of Light Emitting Diodes (LED) has stimulated reconsideration of both
[14]
the concept of comfortable lighting, and questions about the applicability of existing standards
[14][15]
to environments illuminated by LEDs. Although we will not discuss direct glare in detail in
this paper, the specification of limits for the ambient illuminance for office computer workplaces in
standards such as EN 12464-1 overlaps with the discussion of unwanted reflections from the inactive
and active areas of displays that are visible during use.
Moreover, there is at least one specification within the ISO 9241-3xx series that deals specifically with the
issue of direct glare as defined and discussed by CIE and ISO 9241-6:1999, 3.9, 5.4, Clause 10 and Annex A.
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ISO/TR 20278:2015(E)
ISO 9241-303:2011, D.5 states a requirement regarding the upper limit for LH, display screen luminance:
“Glare (disability glare or discomfort glare) shall not be produced by the display”. Clearly this refers
to a limit on direct glare resulting from an excessively high luminance of a self-luminous object (the
display) located in the visual field, especially near the line of sight, exactly satisfying the definition
of direct glare.
3.3 Glare by reflection
The second type of glare discussed in ISO 9241-6 is glare by reflection:
“Glare by reflection can occur in vertical, horizontal and intermediate planes. It can impair visual
perception and/or cause discomfort. Disturbing glare caused by reflection on working surfaces and
work equipment (for example, visual displays, printed documents, keyboards) should be prevented
by suitable design and positioning of the work equipment and the lighting.”
The majority of the discussion on glare within the context of the ISO 9241-3xx series pertains to indirect
glare resulting from reflections from display surfaces. The context of use for the great majority of the
current standards content in the ISO 9241-3xx series is in regard to displays in the office computer
workplace, however, this may be expanded in the future to include the home and other environments. It
will be critical to maintain distinctions between specifications developed for different environments or
contexts of use. It is also important to determine what is meant by the term “disturbing glare”, as this
term is not defined by the CIE and does not appear to be used outside of Europe.
4 Visual discomfort and glare while using computer displays
4.1 Asthenopia
Visual discomfort while viewing displays is commonly referred to as computer vision syndrome or
asthenopia while viewing computer displays. Asthenopia complaints from computer users are common,
[16]
with estimates of current symptom prevalence ranging as high as 90 % of all computer users. It is an
[17]
issue well known and documented since the introduction of personal computers.
[18]
Sheedy, et al. list potential causes for asthenopia:
“Direct glare from lighting, anomalies of binocular vision, accommodative dysfunction, uncorrected
refractive error, compromised quality of the viewed image, less than optimal viewing angles,
flickering visual stimuli such as CRT computer displays, and dry eye”.
Sheedy further classifies asthenopic symptoms into two groups, internal and external, based on a
principle components analysis of the responses made by subjects during a study of asthenopia. The
external symptom factor included eye symptoms such as burning, irritation, and dryness. These
symptoms were associated with inducing conditions such as glare, upward gaze angle, flicker, font size,
and reduced blink rate.
The internal symptom factor included symptoms such as eyestrain, headache and eye ache, they were
associated with inducing conditions such as astigmatism and close viewing distance.
Consequently, while glare is an important causal factor for asthenopia occurring in the office computer
workplace, it is important to note that it is one of many causal factors.
5 Unwanted reflections from displays
5.1 General
The question currently before ISO TC 159/SC4 technical committee is that of glare from the inactive
areas of the display, such as housings, that are visible during use. It has been proposed that a limit
should be set on the reflectivity (specular gloss) of equipment housings visible during use. In order
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ISO/TR 20278:2015(E)
to more fully understand the issue of glare, this paper first reviews current regulations, technical
standards and research findings pertinent to unwanted reflections (glare) from the active and inactive
areas of displays.
5.2 Glare and unwanted reflections on screens in the ISO 9241-3xx series
The ISO 9241-3xx series of ergonomic standards addresses the issue of unwanted reflections (glare)
on display screens, with regard to the effect on the computer user’s comfort and his or her visual
performance. The terms “glare” and “unwanted reflections” are used interchangeably within the
ISO 9241-3xx series. We will adopt the usage of the term “unwanted reflections” in this paper, with the
understanding that it is used to mean both glare and unwanted reflections.
NOTE ISO 9241-305 also uses the term “glare” to refer to a noise source during measurement and unwanted
reflections to refer to reflected light interfering with human visual performance.
6 Pertinent regulations regarding glare and unwanted reflections
6.1 European Directive 90-270 — On the minimum safety and health requirements for
work with display screen equipment
[19]
EU Directive 90-270, which has the force of law for members of the European Union, offers several
statements regarding glare and unwanted reflections on screens.
“The screen shall be free of reflective glare and reflections liable to cause discomfort to the user.”
“Possible disturbing glare and reflections on the screen or other equipment shall be prevented by
coordinating workplace and workstation layout with the positioning and technical characteristics
of the artificial light sources.”
“Workstations shall be so designed that sources of light, such as windows and other openings,
transparent or translucid walls, and brightly coloured fixtures or walls cause no direct glare and
no distracting reflections on the screen.”
6.2 The meaning of disturbing glare within the ISO 9241-3xx series
6.2.1 General
Glare by reflection has been defined by the CIE; however, it is not clear what is meant within the context
of EU Directive 90-270 by the term “disturbing glare” as it is not defined by the CIE and does not appear
to be in common use outside of Europe.
ISO 9241-307 addressed this issue by equating “disturbing glare”, as used in EU Directive 90-270, to the
CIE definition of glare with the following statement:
“Disturbing glare thus is a condition of vision in which there is a disturbing degree of visual
discomfort or/and a noticeable reduction in the ability to see details or objects.”
thus explicitly referencing and adopting the CIE definition of glare:
“Condition of vision in which there is discomfort or a reduction in the ability to see details of
objects, caused by an unsuitable distribution or range of luminance, or too extreme contrasts”.
6.2.2 CIE definitions of discomfort glare and disability glare
[20]
The CIE defines discomfort glare verbally as
“glare which causes discomfort without necessarily impairing the vision of objects”,
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ISO/TR 20278:2015(E)
and quantitatively, in the context of direct glare caused by indoor lighting, by means of the Universal
[12]
Glare Rating (UGR) formula.
The CIE defines disability glare verbally as
[13]
“Disability glare is glare that impairs vision.”,
[13]
and quantitatively by means of the CIE General Disability Glare Equation. The CIE general formula
for discomfort glare caused by indoor lighting is
2 2
UGR = 8 log [(0,25/L )∑L ω/ρ (1)
10 B
where L is the background luminance and may be defined as E/π, where E is the indirect illuminance at
B
the eye of the observer and is measured in lux, ω is the solid angle of the glare source, L is the luminance
of the source luminaire in the direction of the user’s eye, and ρ is the Guth position index.
Although the original Guth position index was described only for the upper half of the visual field, it has
[21]
been extended by Kim, et. al. over the entire visual field. For the visual angles typical of a computer
[21]
viewer (about 20° above, below and to the side of the line of sight), it is approximately 1, which is
[22]
smaller than the value suggested by Luckliesh and Guth, which is about 1,5 for the overlapping regions.
While the CIE discomfort glare rating was developed in the context of direct glare, Howarth and
[23]
Hodder have examined whether it can be used to estimate the value of a single source luminance
that will create an unacceptable reflectance. They note that it required a source luminance many times
that which would be expected in the work environment in order to produce a reflection that would have
an unacceptable UGR rating.
6.2.3 Unwanted reflections as currently specified and limited in ISO 9241-303, 9241-305 and
9241-307 for the active area of displays (screens)
Currently, ISO 9241-307 specifies maximum acceptable levels of unwanted reflections on the screen
(the active area of the display) in terms of contrast ratios, which incorporate diffuse and specular
reflection components. It is important to note that both ISO 9241-305 and ISO 9241-303 emphasize the
importance of correctly dealing with the haze component.
In ISO 9241-303 we find the following note:
“Typical LCD (liquid crystal display) monitor screens, for example, comprise only haze components
with varying width of the intensity distribution of reflected light; in this case, specular and
Lambertian components can be neglected.”
ISO 9241-305 emphasizes the necessity to account for any haze component in the determination of the
specular component of glare luminance. In the case that
“…examination of the appearance of the reflected light of the lamp from the position of the LMD
showed that the virtual image is distinct but there is substantial luminance reflected beyond the
virtual image of the source or no virtual image is observable except for a “fuzzy ball of light”, then
calculate the small-source specular reflectance, ρ , while attempting to subtract the diffuse
small
background from the specular component using the luminance factor, ρ , obtained from 6.5.6.”
D
It further cautions that this:
“…is an approximate attempt to account for the non-specular reflectance by subtracting it from the
specular component. The method specified [in this case] is correct for reflective surfaces for which
only a specular and diffuse (Lambertian) component of reflection exists. It does not properly subtract
the haze contribution from the reflection. It is a naïve model and can generate confusing results, owing
to the assumption by its users that they have the correct specular reflectance and can begin using the
form L = ρ Ls with impunity.”
small
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ISO/TR 20278:2015(E)
6.3 Interaction between specular, diffuse and haze reflection components
6.3.1 General
Attention is called to the distinctness or sharpness of the reflected image, noting that the more distinct
[24][25][26][27]
an image is, the more noticeable and disturbing the image becomes. However, it is noted in
Reference [27] that haze reflection counteracts the effect of specular reflectance.
“The effect from haze reflection relates positively to [the acceptable magnitude of the source
luminance] because the haze reflection helps blur the edge and lower the peak luminance of the
reflection. Both actions contribute to the reduction of perceived contrast. With less perceived
contrast and blurred edges, the source of the reflection can have a higher luminance before being
considered disturbing.”
Reference [27] describes a source luminance that is on the borderline between acceptable and
disturbing as
Log10(L ) = 3,013 – 10,668 ρ + 0,43 H + 0,001 L – 4,550 ω (2)
A S B
where L is the source luminance creating the disturbance, ρ is the specular reflectance associated
A S
with angular size of the light source, H is the haze reflection, L is the background luminance of the
B
screen, and ω is the solid angle that the reflected light source subtends at the viewing position.
6.3.2 Recognition of the interaction of unwanted reflection components in the ISO 9241-3xx
series
The ISO 9241-3xx series specifically recognizes the interaction between specular and diffuse reflection
components in determining the point at which unwanted reflections are unacceptable. For example,
both ISO 9241-305 and ISO 9241-307 limit the allowable reflection luminances for positive polarity
screens displaying artificial information as
-0,65
(L /(L + L )) ≥ 1,2 + 4,84(L + L ) (3)
H D S D S
and
(L + L + L )/(L + L ) ≤ 1,25 (4)
H D S H D
where L is the luminance of the display at its high state, L is the luminance due to diffuse reflection
H D
and L is the luminance due to the specular reflection.
S
7 Luminance balance
ISO 9241-307 recommends that:
“In work environments, the luminance of the task areas, Ltask, area, that are frequently viewed
in sequence while using the visual display (document, covers, etc.) should be between 0,1 × Ltask,
area ≤ LEa, HS ≤ 10 × Ltask, area, where LEa, HS is the area average luminance of the visual display.”
8 Glare and the ambient illumination in the office-working environment
8.1 Ambient illuminance
ISO 9241-307
...
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