Bezel gloss and glare

Displays 25 (2004) 77–87 www.elsevier.com/locate/displa

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 * Corresponding author. Tel.: C44-1-509-223-040; fax: C44-1-509223-904. 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. 0141-9382/$ - see front matter q 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.displa.2004.07.002

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.

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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.

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 respectively, 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.

Fig. 1. The characteristics of a reflection depend upon the surface gloss, as may be seen by comparing the reflections of the fluorescent lamp in the screen and the bezel.

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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 StilesHolladay 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

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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, silvergrey, 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 silvergrey 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.

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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).

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

Fig. 3. The left panel shows the display with a reflection. The right panel shows the visual performance at each of the forty-six screen positions, the y axis scale showing the percentage of the maximum character luminance possible, as described in the text.

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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 approximately 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 approximately 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 Matt black surround Glossy black surround Stainless steel surround Matt White surround

24,000 24.4

268 24.4

89 0

100 0.1

19,620

28

100

79.5

472,000

1160/160a

714

374

370

0.011

Off the scale (over 2000) 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.

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For our current purposes, we define contrast as ((LtaskK Lsurround)/(Lsurround)) which is calculated as: reflection luminance K bezel 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 glarefree 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

PH SC SH TC Average s.d.

Standard (without reflection)

Standard

Matt White

Matt Black

Glossy Black

Mirrored

94.3 94 91.7 91.7 92.9 1.4

83 90 79 81 83.3 4.8

83 90 79 79 82.8 5.2

81 90 79 79 82.3 5.3

83 90 79 79 82.8 5.2

81 89.3 65 75 77.6 10.2

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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 secondhighest 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 intraocular 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 environments 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, encapsulated 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

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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

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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) 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.

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4 is the mid-point of these two extremes, meaning barely acceptable. 2. How legible did you consider the text to be from 1 (not at all legible) to 7 (fully clear and distinct) 4 is the mid-point of these two extremes, meaning barely legible. 3. How much visual discomfort did you experience during the trial from 1 (no discomfort) to 7 (extreme discomfort) 4 is the mid-point of these two extremes, meaning some or minor discomfort. 4. 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) 4 is the mid-point of these two extremes, meaning barely 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 workstation 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

Table 3 The gloss of the eight surrounds Display/Surround

Gloss at 208

Gloss at 608

Mean rank

Standard light silver-grey flat panel display (‘FPD standard glossy’) Semi-matt light silver-grey flat panel display (‘FPD standard semi-matt’) Matt light silver-grey flat panel display (‘FPD standard matt’) Glossy black surround (‘FPD glossy black’) Stainless steel surround (‘FPD stainless’) Matt black surround (‘FPD matt black’) Glossy CRT display (‘CRT glossy’) Matt CRT display (‘CRT matt’)

100

102.7

2.5

2.6

15.2

6

3.0

16.7

5

79.5

88.4

4

Over 2000 0.1

Over 1000 0.7

1 8

93.8 2.3

108.2 15.1

2.5 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.

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 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 B C D E

595 670 310 220 500

900 800 400 345 550

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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.

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

Fig. 5. Responses to questions 5 and 6. The data from question 5 has been normalized so that a neutral response scores zero. The descriptions of the bezels are found in Table 3.

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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 disturbing. (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 conditions. 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 silvergrey, 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

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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 inconsistencies 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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