Bezel gloss and glare

Bezel gloss and glare

Peter A. Howarth*, Simon G. Hodder

Visual Ergonomics Research Group, Department of Human Sciences, Loughborough University, Leicestershire LE11 3TU, UK

Received 25 March 2004; accepted 8 July 2004

Available online 3 August 2004

Abstract

Two studies were performed to examine whether reflections in the glossy surround of computer displays gave rise to ergonomic problems

of reduced visual performance or discontent. The approach taken was not to assess whether or not problems were present under typical

environmental conditions, which would risk missing problems, but rather was to determine conditions under which problems did exist. Once

this was done, it was then possible to evaluate whether the gloss of commercially available products would be acceptable or unacceptable in

more normal surroundings.

In the first study, visual performance was assessed by evaluating sensitivity to contrast when five different screen surrounds (‘bezels’) were

used. All six of the participants showed a decrease in sensitivity when the reflection of a lamp, of luminance 1000 times that of a typical

fluorescent lamp, was seen in a mirror-like surround. When a black glossy surround was used, a tiny decrement was seen for two older

participants, who were past the UK retirement age, but not for the other four pre-retirement age participants. No decrement was detected

when a light silver-grey glossy surround was used. When the lamp luminance was reduced by a factor of 100 (but was still 10 times higher

than that of a typical fluorescent lamp) no decrement was seen in the performance of any of the participants, even when the mirror-like

surround was used.

In the second study, assessments were made of the displays on five different subjective scales following the reading of text for 20 min.

Eight surrounds were used, three of which were identical in every respect, apart from the glossiness of their bezels. Variation in acceptability

was found amongst the surrounds, and both a shiny mirror-like surround and glossy black surround were considered to be unacceptable

overall. However, the comparison between the three identical displays revealed no significant differences in acceptability, and we conclude

that gloss per se does not give rise to ergonomic problems in acceptability unless there is a very high contrast between the reflection and the

surround.

q 2004 Elsevier B.V. All rights reserved.

Keywords: Bezels; Flat panel displays; TCO’03

1. Introduction

Since the widespread introduction of personal computers

in the 1980s there has been a continual development of the

visual displays1 they employ. The evolution in these

0141-9382/$ - see front matter q 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.displa.2004.07.002

* Corresponding author. Tel.: C44-1-509-223-040; fax: C44-1-509-

223-904.

E-mail address: [email protected] (P.A. Howarth).1 In this paper these terms are used with the following specific meanings:

Display: the complete piece of hardware which makes up a computer

monitor, including the screen and the case. Cathode Ray Tube (CRT): the

complete display device using this screen technology. Flat Panel Display

(FPD): the complete display device incorporating Flat Panel technology

Screen: the active part of a display device Bezel: the portion of the display

immediately adjacent to the screen.

displays brought about by the change in their usage, from

being text-based interfaces to graphical user interfaces to

interfaces for the viewing of moving pictures, has been

accompanied by a continual improvement in hardware. Flat

panel displays (FPDs) with high resolution screens are

becoming commonplace, and a number of manufacturers

are now producing displays which present a high definition

image to the user.

The ‘law of diminishing returns’ now applies—one

needs a large change in the screen to produce even a small

improvement in visual quality, and style is playing an

increasingly important role in the marketplace. It is

now unusual to find a dull grey or beige display, and

black, silver or white units are more common, as are high

gloss finishes.

Displays 25 (2004) 77–87

www.elsevier.com/locate/displa

http://www.elsevier.com/locate/displa

P.A. Howarth, S.G. Hodder / Displays 25 (2004) 77–8778

These changes to the displays are being driven by

aesthetics and style, rather than by the needs of the user in

terms of visual comfort and performance. Consequently, we

need to ask whether there are any adverse effects of their

introduction. Concern about such effects has led the

Swedish Confederation of Professional Employees to

restrict both the reflectance and glossiness of display

surrounds (‘bezels’) in their latest guidelines [20]. This is

despite the fact that, as they note, there is little scientific

evidence to indicate how bezel reflectance and glossiness

actually affect users.

The effect of gloss can be seen in Fig. 1. The screen has a

matt finish and so the reflection of the fluorescent lamp in it is

spread out. The bezel, however, is glossy and so the reflection

has sharply defined edges and is of a higher luminance.

Glare produced as a consequence of the glossiness of a

bezel could have two effects. The reflection of a light source

situated behind the user could produce discomfort or it

could result in disability, manifest as a reduction in visual

performance. Two studies are reported here which deal with

these issues. In the first, for five different surrounds, visual

performance was evaluated in the presence of a glare source

reflected in the bezel. In the second, a panel of participants

gave subjective opinions about each of eight different

displays, viewed under normal lighting conditions, after

having read text from the screen for twenty minutes.

The results of both studies indicate that the glossiness of

a bezel should not be a problem to a computer user under

any normal circumstances.

Fig. 1. The characteristics of a reflection depend upon the surface gloss, as may be

the bezel.

2. Study 1: Visual performance

2.1. Theoretical background

A reflection in a bezel cannot directly affect visual

performance, in the way that a reflection on the screen can

reduce the contrast between a character and its background

by raising the luminance of both. However, a strong

reflection could affect the eye rather than the visual task,

and this effect has long been recognized in other situations

[8–10,22]. CIE report 31 [3] treats disability glare as

essentially an issue of equivalent veiling luminance, and the

disabling effect of the glare source can be calculated by

determining the effective contrast reduction of the task. This

is achieved by use of the ‘Stiles-Holladay disability glare

formula’ which is described in the CIE report [18, 19].

To calculate the effect of a reflection in a bezel let us take

the extreme example of a lamp with a luminance of

10,000 cd mK2 reflected in a mirror-effect bezel reflecting

all of the incident light. If the lamp were positioned such

that its image was 3 m from the eye, at an angle of 108 from

the line of sight, then the illuminance at the plane of the eye

would be 1090 lux and the veiling effect would be

109 cd mK2. If, for example, the screen character and

background luminances were 10 and 100 cd m,K2 respect-

ively, then the veil would raise these values to 119 and 209.

This would still provide a difference, which would be well

above the contrast threshold of the eye (typically 1–2%) and

the character would still be clearly visible.

seen by comparing the reflections of the fluorescent lamp in the screen and

P.A. Howarth, S.G. Hodder / Displays 25 (2004) 77–87 79

This calculation indicates that the reflection in the bezel

is unlikely to directly affect visual performance, for people

with normal vision, under any condition other than when

the screen task is of extremely low contrast. The Stiles-

Holladay formula has been refined recently, and Vos and

van den Berg [21,22] have proposed modifications to take

into account the observer’s age and eye colour. The data of

Ijspeert et al. [14] shows that a cataract-free person of

70 years of age will suffer twice as much from veiling glare

as a young person, but even a two-fold increase in veiling

would have little effect on visual performance when

viewing the above display.

From these calculations, which have used realistic

illuminance values and the extreme case of a mirror-like

bezel, there is no reason to suppose that disability glare will

adversely affect visual performance for a bezel with a more

normal appearance.

2.2. Empirical study

2.2.1. Introduction

On the basis of these calculations one would not expect

disability glare from a bezel reflection to be a problem under

normal office or home conditions. However, in order to

establish convincingly whether or not this is the case, it is

not enough to simply show that no effect occurs. In addition,

we need to find the threshold conditions under which an

effect can be shown to be present in order to establish that

normal conditions are less extreme.

In this first study, visual performance was evaluated by

determining the minimum contrast detectable using letters

displayed on a FPD. By using letters of a constant size, in

the manner of Pelli et al [15], the technique measures the

eye’s sensitivity to contrast and not to size. The use of low

contrast characters has been shown to be a more sensitive

technique than the use of high contrast characters to

evaluate visual changes, such as those found with age [7].

This technique is more appropriate in the current context

than one assessing size threshold for letters, as one might

expect disability glare to affect sensitivity to contrast more

than sensitivity to letter size.

Five different bezels, of different reflectance and gloss,

were compared under conditions of glare. One was the

standard bezel of a high-quality FPD currently available on

today’s market. The other four were masks, which overlaid

the standard surround, and allowed the trials to be

performed using the same screen. In each case the visual

performance decrement produced under glare conditions

was evaluated.

2.2.2. Method

2.2.2.1. Conditions. The tests were performed in the Visual

Ergonomics Research Group laboratories. The screen was

viewed either under normal laboratory lighting—in which

case no specific reflections were apparent—or with an extra

light (glare) source placed directly behind the participant.

This condition simulated the worst configuration likely to be

found in the office or home environment, the reflection

being directly adjacent to the test stimulus (as can be seen in

the upper panels of Fig. 2 below.

The glare source used was a photoflood lamp (KFB 3007

SFK 1000 W) which produced 7,100,000 cd mK2. This is a

far higher luminance than would be found in normal

circumstances, and this lamp was used to ensure that a

measurable performance decrement was present.

The characters were presented on a high quality

commercially available 15 00 FPD which had a light, silver-

grey, glossy bezel. The display was used either in its normal

configuration (Fig. 3) or with one of four masks (Fig. 2)

covering the bezel. These masks were:

,
Matt black finish
,
Matt white card
,
Glossy black finish
,
Stainless steel (Mirrored) surface
It was intended that a performance comparison between

the matt black finish and the glossy black finish would

provide a direct evaluation of the effect of gloss, and a

comparison between the matt white card and the light silver-

grey glossy bezel would give an approximate evaluation of

this effect. The mirrored surface was included to provide an

extreme case of ‘gloss’.

2.2.2.2. Participants. In total, six participants were tested.

Four were chosen to represent the age and vision ranges

normally found in the working population, and these people

took part in the main experiment. Two further participants,

past retirement age, were tested in a control experiment to

confirm that the findings were valid for older participants.

All participants were practiced computer users.

SC, female, age 22, PhD student, familiar with vision

testing

SH, male, age 35, Research assistant, some experience of

vision testing

PH; male, age 48, Vision scientist, experienced in

psychophysical testing

TC; male, age 63, retired, no experience of vision testing

JE; male, age 66, retired, no experience of vision testing

DE; female, age 69, retired, no experience of vision

testing

All participants had distance visual acuity in their

preferred eye of at least 6/6 (20/20); with the exception of

SH who had reduced vision (as a consequence of childhood

retinal trauma) with acuity in his better eye of 6/12 (20/40).

TC wore an intermediate correction for the test (performed

at a distance of approximately 50 cm) and the other

participants wore any correction that they habitually used

for VDU work.

Fig. 2. The four masks used to alter the bezel appearance.


2.2.2.3. Visual performance test. A total of 33 different slides

were produced as a Microsoft PowerPoint presentation.

PowerPoint has the facility to change the RGB output to the

screen in small increments, and successive PowerPoint slides

each contained a line of text of increased darkness, providing

an increased contrast with the light background.

Each slide contained a single line which was composed

of 46 alphanumeric characters of 18 point font size,

consisting of a mixture of letters and numbers (see Fig. 3).

Fig. 3. The left panel shows the display with a reflection. The right panel shows the

showing the percentage of the maximum character luminance possible, as describ

This size of character was deliberately chosen so that the

characters would be easily seen by all participants when the

contrast was great enough. In this way we avoided

confounding size and contrast as metrics.

Participants sat with their head fixed in position by means

of a head-rest. The restraining of the head in this manner

was necessary so that the position of the reflection did not

change. The test was performed monocularly, with

participants using their preferred eye (L for SH, R for

visual performance at each of the forty-six screen positions, the y axis scale

ed in the text.


the others). The reason for the use of only one eye is that

visual performance would be expected to be better under

binocular conditions if the vision from one eye could be

used to compensate for (and hide) a decrement in the other

eye. Thus any decrease in the performance of one eye

affected by the gloss could be masked if the other eye were

unaffected.

MS PowerPoint allows the specification of character

luminance by the control of the RGB guns, in terms of

percentage. The background for the test was run at 96% and

the test characters were run at lower percentages to produce

dark characters on a light background. As the software and

screen produced a luminance variation, which was approxi-

mately linear over the short range used (i.e. the luminance

was proportional to the gun percentage) the character

percentage was taken as the metric for the dependant

variable in the experiment.

2.2.2.4. Environmental conditions. A Hagner S3 universal

photometer (#S394209) was employed to measure the

environmental conditions. This photometer has an operating

range for the measurement of luminance which ends at

2,00,000 cd mK2. When the luminance was above this

value, the measurements were obtained by reducing the

radiation entering the meter by a factor of 100, using two

neutral density filters, and subsequently multiplying the

recorded value by this factor. Gloss was measured using a

Minolta Multi-gloss 268 (serial # 9221722).

2.3. Results

2.3.1. Bezel luminance

Table 1 shows the luminances, gloss and contrast for

the different bezels. The reflection luminance was

determined with the photoflood lamp positioned at a

distance of 150 cm. from the display; the bezel luminance

was assessed at a point adjacent to the reflection. “The

reflection in the bezel subtended an angle of approxi-

mately 28 in both the horizontal and vertical meridians.”

Table 1

Luminances recorded from the bezel (cmK2)

Bezel

(Surround)

Reflection

luminance

Bezel

luminance

Contrast Gloss (208)

Standard FPD 24,000 268 89 100

Matt black

surround

24.4 24.4 0 0.1

Glossy black

surround

19,620 28 100 79.5

Stainless steel

surround

472,000 1160/160a 714 Off the scale

(over 2000)

Matt White

surround

374 370 0.011 1.9

a The two values were taken from points immediately adjacent to the

reflection (higher value) and at the bottom of the surround. For the contrast

calculation the mean value of 660 was employed.

For our current purposes, we define contrast as ((LtaskKLsurround)/(Lsurround)) which is calculated as:

reflection luminance Kbezel luminance

bezel luminance

Under normal laboratory lighting, with the glare source

unlit, the illumination was 250 lux in the plane of the screen,

and 580 lux in the horizontal plane.

2.3.2. Test results

2.3.2.1. Participants PH, SC, SH and TC. Fig. 3 shows, on

the left, the appearance of the standard FPD when the glare

source was lit. The diffuse reflection in the matt screen and

the sharp reflection in the glossy bezel are apparent. The

right panel of this figure shows the visual performance

change for PH across the screen, and the decrement brought

about by the reflection in the screen is clear.

The measure adopted clearly showed a performance

decrement at the edge of the screen. The two possible causes

of this decrement are the direct effect of the glare source on

the screen itself, and the indirect effect of the bezel reflection

on the eye. Given that the two effects would be expected to be

additive, the effect of the bezel reflection can be evaluated by

assessing whether there is a change in the decrement for

different bezels. This is because the same screen and the

same lighting conditions were used in all trials, and so the

direct effect on the screen would be constant.

The crucial issue is the visual performance at the very

edge of the screen, adjacent to the reflection. This is the

position that would be affected to the greatest extent by the

bezel reflection, and if the character in this position were not

affected then none of the other characters would be affected.

The results for this position (the 46th character) are shown

in Table 2 for four participants.

Inter-observer differences were apparent. On average,

the youngest participant (SC) performed the best and SH

and TC performed the worst. For each observer the

performance using the mirrored bezel was always the

worst, but there were no significant differences amongst

the other conditions (with the exception of the initial glare-

free condition).

Table 2

The visual performance at the position of the final alphanumeric character,

adjacent to the reflection in the bezel. The reflection was present in each

case, apart from the first ‘standard’ condition, as indicated

Standard

(without

reflection)

Standard Matt

White

Matt

Black

Glossy

Black

Mirrored

PH 94.3 83 83 81 83 81

SC 94 90 90 90 90 89.3

SH 91.7 79 79 79 79 65

TC 91.7 81 79 79 79 75

Average 92.9 83.3 82.8 82.3 82.8 77.6

s.d. 1.4 4.8 5.2 5.3 5.2 10.2


2.3.2.2. Participants JE, DE. The differences under glare

conditions between SC, PH and TC are in agreement with the

age rank. One might expect that older participants would show

greater loss, given that people become more sensitive with age

to this form of glare [6]. Consequently, two older participants

(JE, DE) were then tested. Both showed a small performance

decrement on the final two letters of the line when the stainless

steel surround was used in conjunction with the high intensity

lamp. However, there was virtually no performance difference

between the glossy black surround (which had the second-

highest contrast between the reflection and the bezel) and the

remaining bezels. No performance decrement whatsoever

was seen for any of the other conditions.

2.4. Discussion, Study 1

From the analysis of experimental and theoretical results

found in other circumstances, one would expect that visual

performance would only be affected by disability glare from

a reflection in a display bezel under extreme circumstances.

This expectation was confirmed empirically using three

working-age participants with normal vision and one with

reduced visual acuity, and two older participants who were

over the UK age of retirement.

The empirical investigation used a method of assessing

visual performance which is highly sensitive to the effect of

scattered light on a VDU screen. Using this method, under

conditions far more extreme than would be found in a

normal office environment, we found no decrement in

performance with a commercially available standard light

silver-grey glossy FPD as a consequence of the glossiness of

the surround. Furthermore, we found no significant

difference between a glossy black and a matt black bezel,

nor between a matt white bezel and the standard silver-grey

glossy FPD, even under the extreme conditions employed.

Although we have used only a small number of observers,

there is no indication that the use of further participants

would in any way alter the conclusions. The fact that SH, who

has significant media opacities leading to increased intra-

ocular scatter, showed no performance difference between

the glossy and matt bezels indicates that it is highly unlikely

that people with normal vision would suffer any decrement

for any bezel other than, perhaps, the mirrored one.

Under the extreme conditions used, we did measure a

small decrement in performance at the very edge of the

screen, adjacent to the bezel, when a mirrored surround was

introduced. All other positions on the screen were unaffected.

However, it must be noted that the lamp luminance needed

to produce this decrement was so high that it was outside

the range of the photometer. Conditions this extreme2 would

2 If such extreme conditions are encountered, for example on a clear day

when the sun is low in the sky, other reflective surfaces, such as the screen

itself, will also be affected by the glare. The problem here is the

environment and not the equipment, and the solution is to provide

environmental control.

not be found in a normal office or other working environ-

ments where such a display would be used.

In a follow-up experiment, the luminance of the lamp

was reduced by a factor of 100, at which point the

performance decrement at the position of the final

alphanumeric character was too small to measure for any

of the six observers for any bezel. The lamp luminance at

this point was 71,000 cd mK2 and, to put this into

perspective, a typical value for a fluorescent tube is between

2000 and 7000 cd mK2. Thus we conclude that even a

mirror-like surround would be unlikely to cause a visual

performance decrement under typical office or home

conditions for the participants tested. As the bezel of the

commercially available FPD reflects far less light than the

mirror-like surround we conclude that it will not adversely

affect visual performance under any normal conditions.

3. Study 2: Subjective opinion

3.1. Theoretical background

A bright light shone into the eye will often cause

discomfort. Although the physiological mechanism, which

underlies this sensation is not yet understood, the conditions

which produce the discomfort have been extensively studied

[2]. The primary source of this knowledge has been the

evaluation of indoor environmental conditions, encapsu-

lated in the Commission Internationale de l’Eclairage (CIE)

report 117 [ 4].

In essence, the discomfort reported varies with the

luminance, size and position of the glare source and the

luminance of the surround in a known manner. Although

there are significant differences between people in the

magnitude of the discomfort they report under given

conditions, the human response can be typified by the CIE

Unified Glare Rating [17]. The value for the Unified Glare

Rating (UGR) for a single glare source is found from the

formula:

UGR ¼ 8 log10 ð½0:25=Lb�!½L2 !u=p2�Þ

where

Lb
the background luminance (cd mK2)
L
the source luminance, measured at the observer’s eye
(cd mK2)

u
the solid angle of each source at the observer’s eye
(steradian)

p
the ‘Guth’ position index
To evaluate the effect of bezel reflection, we can apply

this formula by taking the example, from Study 1, of a

glossy black bezel illuminated by an intense source with a

luminance of 7,100,000 cd mK2. The luminance of the

reflection was 19,620 cd mK2, the surround luminance was

28 cd mK2, and for the calculation we can take the reflection

3 In a control experiment designed to investigate the effect of exposure

time upon participants responses, 10 participants sitting at their normal

workstation completed the questionnaires 20 min after commencing work,

and again at the end of the day. No significant differences were found

between the two sets of responses.


to be approximately 28 in diameter, and 38 from the edge of

the active portion of the screen when viewed from a distance

of 50 cm. From the CIE formula we obtain a UGR rating of

27, which would be expected to produce complaints of

discomfort from a significant number of people working

under these conditions constantly. However, it is still within

acceptable limits for general activities in ‘circulation areas

and corridors’ [1] which specify a UGR limit of 28.

If we now reduce the lamp luminance to 70,000 cd mK2

(still over 10 times the luminance of a normal fluorescent

lamp) we reduce both Lb and L by a factor of 100, and we

obtain a UGR rating of 11.1. This value is well below the

minimum value for UGR considered acceptable for any

interior environment [1]; in fact, a value of 13 on this scale

represents ‘least perceptible glare’ and so it is unlikely that

any individual would be bothered by discomfort from this

reflection.

From these results it seems highly unlikely that under

more realistic conditions, with lower luminance lamps,

discomfort from glare would be a problem. Although on

theoretical grounds we would not expect glare from a

reflection in a bezel to give rise to discomfort, users could

dislike glossy surrounds on the basis of some other

criterion, such as irritation with the presence of a reflection.

To investigate this issue, the second study determined the

subjective acceptability of a number of very different

bezels.

3.2. Empirical study

3.2.1. Introduction

In the second study, twenty people read text from each of

eight displays, all of which had a different surround to the

screen. The aim of the study was to determine which of

these surrounds participants were content with, and which

were not considered to be satisfactory. To this end,

participants completed an evaluation questionnaire about

each display after reading a story shown on it.

3.3. Method

3.3.1. Conditions

The range of displays was extended from Study 1 by the

inclusion of two CRTs, and two further FPDs. One CRT had

a high-gloss silver-grey bezel, and is referred to here as the

‘glossy CRT’. The other had a traditional beige matt

surround, complying with TCO’03, and is referred to here as

the ‘matt CRT’. The two extra FPDs were identical to the

standard FPD used in study 1 (Fig. 1) in every respect except

glossiness. One had a totally matt surround (referred to here

as the ‘matt FPD’) and replaced the white matt card

surround used in Study 1. The other had a 1.5 cm. matt band

immediately adjacent to the screen, and is referred to here as

the ‘semi-matt FPD’. The important point to note about

these three FPDs is that they were identical in every respect

except for their glossiness, and so any differences in

acceptance and preference could only be as a consequence

of the difference in gloss.

To ensure variation in the ambient conditions, five different

locations in the laboratory were used. To prevent order

effects, participants were assigned conditions and locations

on a psuedo-random basis, which ensured that each condition

was employed at each location an equal number of times

and that there was no pattern to the order of presentations.

3.3.2. Participants

Twenty participants were recruited from amongst the

staff and student body of Loughborough University, and all

were paid for their participation. There was no expectation

that age would seriously affect subjective preference so it

was considered acceptable to have a restricted age range

(from 20 to 41 years). All participants were daily computer

users in their everyday life, and none had prior knowledge

of the purpose of the experiment.

3.3.3. Experimental design

All of the participants read text from the eight displays.

To maintain alertness, these were viewed during two

repeated sessions. Four displays were viewed on each

occasion, and the sessions were separated by a minimum of

two days. On each occasion the text was a short ‘Sherlock

Holmes’ story, chosen to maintain participants’ interest and

to ensure that they concentrated on the screen task for the

full time period. Different stories were used on each trial to

prevent boredom. At the end of each trial, after having read

the story for about 20 min3, participants completed a

questionnaire. The questionnaire was divided into three

sections, comprising of visual analogue scales, rating

responses, and open questions.

In the first section of the questionnaire, four questions

addressed the issues of (1) irritation (2) legibility (3)

comfort and (4) visual comfort (pleasantness). The

responses were recorded on a visual analogue scale,

following the procedure used by Schenkman et al. [16]. In

this procedure, participants were presented with horizontal

lines, labelled 1 and 7 at the ends, and 4 in the middle, and

were instructed to put a mark across the line to indicate how

they judged the issue. Although the scales may not be

intuitively appropriate, given that one might expect

responses to be correlated, they have been used here to

replicate previous work.

The questions asked [16] were:

1.
How irritated and disturbed visually did you feel when
you were looking at the screen from 1 (very irritated) to 7

(fully acceptable and enjoyable)

Table 3


The gloss of the eight surrounds
4 is the mid-point of these two extremes, meaning barely
acceptable.

Display/Surround Gloss Gloss Mean
2. at 208 at 608 rank
How legible did you consider the text to be from 1 (not at

all legible) to 7 (fully clear and distinct)

Standard light silver-grey flat panel 100 102.7 2.5

display (‘FPD standard glossy’)


legible.
Semi-matt light silver-grey flat panel 2.6 15.2 6 3. display (‘FPD standard semi-matt’)
Matt light silver-grey flat panel 3.0 16.7 5

How much visual discomfort did you experience during

the trial from 1 (no discomfort) to 7 (extreme discomfort)

display (‘FPD standard matt’)

Glossy black surround (‘FPD glossy 79.5 88.4 4

4 is the mid-point of these two extremes, meaning some

or minor discomfort.
black’) 4. Stainless steel surround
(‘FPD stainless’)

Over

2000

Over

1000

1

Matt black surround 0.1 0.7 8

How content were you with the visual appearance of the

computer display you have been using from 1 (not at all

content) to 7 (completely content)

(‘FPD matt black’)

Glossy CRT display (‘CRT glossy’) 93.8 108.2 2.5

Matt CRT display (‘CRT matt’) 2.3 15.1 7

The ranks vary depending upon the angle, and column 3 provides a rank

based on an average of the first two columns. The ‘standard’ FPDs were all

light silver-grey in colour, differing only in their gloss characteristics.

Table 4

The ambient conditions at the five locations

Location Near-vertical illuminance, in

lux, measured at centre of

screen

Horizontal illuminance, in

lux, measured on keyboard

A 595 900

B 670 800

C 310 400

D 220 345

E 500 550


content.

In the second section, question 5 asked participants to

rate twelve different aspects, such as pattern on the bezel

and colour of the bezel, for ‘pleasantness’. One of these

aspects was ‘glossiness of the bezel’. The rating was

performed using a 5-category scale (‘Very unpleasant’,

‘Unpleasant’, ‘Neutral’, ‘Pleasant’, and ‘Very pleasant’.

Participants were then asked, in question 6, to categorise

these same twelve aspects for how ‘disturbing’ they felt

them to be, on a 4-category scale (‘Not at all disturbing’,

‘Slightly disturbing’, ‘Disturbing’, ‘Very disturbing’).

Again, one of these aspects was ‘glossiness of the bezel’.

The participants were unaware of the true aim of the

experiment, and were neither told that the only questions of

interest were those about bezel glossiness, nor that the other

questions were there simply to mask the true item of interest

in the study. This ‘masking’ was designed to ensure that

participants would not be prompted to specifically pay

attention to the bezel glossiness, thereby possibly biasing

their results.

At the end of the session, participants were asked open

questions about other aspects they thought could be

important in determining whether someone found a work-

station pleasant or unpleasant, and whether they thought their

views would change after looking at the screen all day long.

They were also asked to rank the four displays they had seen

that day in terms of their own personal preference, and these

ranks were then summed to provide an ‘Overall Rant Score’.

3.4. Results

3.4.1. Conditions

The measured value of gloss varies with the angle of the

incident light. Table 3 provides the gloss measure of the

eight surrounds at angles of 208 and 608, and the mean rank

order of the displays in terms of glossiness. Ambient

conditions are described in Table 4.

3.4.2. Analogue scale: questions 1–4

The results for these questions are provided in Fig. 4. For

questions 1,2 and 4 a high score is better, whereas for

question 3 a low score is to be preferred. The figures have

been drawn so that, for each question, the higher up the scale

the better.

3.4.3. Rating of pleasantness (question 5) disturbance

(question 6) and overall preference

The results for these questions are provided in Fig. 5.

Surprisingly, there is no significant correlation between

the rank order of gloss (Table 3) and any of the rank orders

in Fig. 5 (Pleasant, Spearman’s RhoZ0.623, Disturbing,

Spearman’s RhoZ0.754, Overall preference Spearman’s

RhoZ0.144).

3.5. Discussion, Study 2

3.5.1. Section 1: Visual analogue scale items

Before examining the subjective opinions about the

bezels, it is worthwhile noting the participants’ bias.

The responses to question 2 (Fig. 4) reveal the

variability within the participant group, and provide us

with valuable information with which we can evaluate the

responses to the other questions. Six of the conditions used

identical FPDs, but with different surrounds (bezels). In

study 1 it was shown that screen legibility is unaffected by

bezel reflections in all but the most extreme conditions

Fig. 4. Responses to questions 1–4. Note that in each case the higher up the scale the better. The descriptions of the bezels are found in Table 3.


(far more extreme than used in this second study). Thus, in

the second study, the surround should NOT affect the

screen legibility, and any differences between these six

conditions can only be caused by other factors (bias) and

not by any actual legibility difference. The range of scores

for the same FPD screen covered 0.51 on the seven point

scale, and this provides us with an indication of the ‘noise’

(or variability) in the data. We can infer that differences

less than this on other questions are not reliable indicators

of real differences.

Fig. 5. Responses to questions 5 and 6. The data from question 5 has been normali

found in Table 3.

Turning now to the issue of acceptability, participants

were asked in question 4 how content they were with the

display. Examination of their responses shows that there

was little to choose between the top five choices, all of

which used flat panel screens. The differences between these

displays were small, and there was NO statistically

significant difference between the first and fifth choice

(the difference of 0.41 was slightly less than the noise

variation of 0.51 discussed above). The participants were

very slightly less content with the glossy CRT, but were far

zed so that a neutral response scores zero. The descriptions of the bezels are


less content with the other two displays, namely the flat

panel with the stainless steel surround and the matt CRT.

The latter was the condition that participants were least

content with, (despite its conformity with TCO’03).

A similar picture is seen in the responses to questions 1

and 3, the main difference being that the glossy CRT

performed much better on these questions than on question 4.

Once again the stainless steel surround and the standard

matt CRT performed at a much lower level than the other

screens.

3.5.2. Section 2: Rating responses

The results obtained for question 5, on the pleasantness

of the bezel glossiness, were normalised so that a neutral

response received a score of zero (Fig. 5). Interestingly, the

results obtained for this question do not faithfully follow the

rank order of glossiness (Table 3).

In overall terms the glossy CRT was rated, on average,

very slightly below zero, and both the glossy black surround

and the stainless steel surround were considered unpleasant.

However, it must be remembered that these were average

values, and there was considerable disagreement amongst

the participants. Two people rated the glossiness of the

stainless steel bezel as pleasant and four rated it as neutral,

three people rated the glossiness of the glossy black

surround as pleasant and two rated it as neutral. The three

identical light silver-grey FPDs (glossy, semi-matt and fully

matt) were all rated, on average, as pleasant, as was the flat

panel with the matt black surround. These four surrounds

were all rated higher than the matt CRT monitor.

The results obtained for question 6, on how disturbing the

gloss was found to be, surprisingly do not follow the rank

order of glossiness, as might have been expected. No-one

reported that the fully matt FPD was disturbing, and only

one person reported feeling that the glossy CRT was

disturbing. However, three people reported feeling that the

glossiness of the matt black surround was disturbing, and

four people reported the semi-matt surround to be disturb-

ing. (Presumably here it was the lack of glossiness that

disturbed them). Only four of the twenty people tested

reported that the standard glossy FPD was disturbing.

Interestingly, of the four people that were disturbed by the

gloss of the semi-matt surround three were not disturbed by

the higher gloss of the standard display. The clear

inconsistency of these responses is one of the most curious

aspects of the results, and indicates (as seen in the answers

to question 2 on legibility) that influences additional to the

gloss were affecting the results.

3.5.3. Section 3: open questions

The unstructured questions revealed little, although few

people felt that their opinions about the surrounds would

change by the end of the day. This result supported the

finding in the control experiment that there was little effect

of exposure time on the ratings.

3.5.4. Overall preferences

In terms of overall preference, (Fig. 5, right scale) the

ranking procedure revealed that there was little difference

between the FPDs with the semi-matt and the totally matt

surrounds, and that there was only a slight preference for

these two in comparison with the standard glossy FPD. The

standard surround was just preferred ahead of the matt black

surround, followed by the glossy CRT then the glossy

black surround. The remaining two conditions, the stainless

steel surround and the matt CRT, were well behind in terms

of overall preference.

4. Overall Conclusions

The conclusion from the first study was that visual

performance was not directly affected by bezel glossiness to

any noticeable extent under normal environmental con-

ditions. This conclusion followed from both the theoretical

analysis and the empirical results of an experiment using

extreme conditions.

The second study looked at subjective opinions, and here

some interpretation is required. A comparison in study 2

between the glossy black surround (79 gloss units at 208)

and the glossy silver-grey surround (100 gloss units at 208)

shows the glossiness of the former to be rated as more

disturbing than that of the latter (question 6). It is probable

that the contrast between the reflection and the rest of the

bezel is higher for the black surround than for the silver-

grey, making the reflection more noticeable [5,12]. Thus, in

terms of the disturbance caused by a reflection (and how

distracting it is) the glossiness cannot be considered in

isolation from the overall reflectance of the bezel.

The results as a whole, and specifically the overall rank

score, indicate that the mirror bezel and the standard matt

CRT monitor were unacceptable (despite the latter’s

conformity with TCO’03) and that the glossy black bezel

was probably just unacceptable. The glossy CRT was on the

borderline of acceptability, whereas the matt black bezel,

and the three silver-grey FPDs were all clearly acceptable.

In this context, one needs to distinguish between, on the

one hand, having preferences and, on the other hand,

something being acceptable or unacceptable. Although it

can be argued that subjective preference provides added

value to a product, in terms of acceptability and desirability,

such preferences are not of concern if the ergonomic criteria

are health, safety and comfort. For example, a pink car may

not be to everyone’s taste, but few would argue against it

being a sound ergonomic choice, on the basis of safety,

because of its conspicuity.

The most notable conclusion of the second study, in the

context of the relationship between the bezel glossiness and

its acceptability, was that there was no consistent difference

in subjective preference between any of the three silver-grey

FPDs. The reason that this conclusion is particularly notable

is that there were no differences between these displays


other than their glossiness. Influences other than gloss—e.g

personal preference for a particular colour, or preference for

a FPD rather than a standard CRT monitor, could well have

affected the overall results of the study, and the incon-

sistencies seen in the responses to questions 4 and 6 can be

explained in this way. However, such additional influences

could not affect the comparison between these FPDs, which

could only be differentiated on the basis of their glossiness.

An alternative explanation for the failure to find a difference

is that our measurement techniques were insensitive, but

this explanation can be dismissed because the techniques

did reveal subjective preference differences amongst the

other displays.

Concern about the effect of gloss on the user has led the

Swedish Confederation of Professional Employees to

restrict both the reflectance and glossiness of display

surrounds (‘bezels’) in their latest guidelines (TCO’03).

This is despite the fact that, as they note, there is little

scientific evidence to indicate how glossiness actually affect

users. The studies reported here show clearly that bezel

glossiness is not, in fact, a major factor in determining

whether a display is acceptable or not from a physical

ergonomics viewpoint in a typical environment. This

conclusion is in agreement with the findings of other

(unpublished) laboratory studies for a display manufacturer

[11,13]. The acceptability, or otherwise, of the displays

appears to depend more on the kansei ergonomics, or the

subjective opinions of the pleasantness of the overall

appearance of the complete unit, than on the physical

reflectance and gloss characteristics of the surround.

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Bezel gloss and glare