This article is reprinted with permission from The Ergonomics Report™ Archives, where it originally appeared on November 17, 2010 — over 3 years ago.
In their introduction, researchers Shin and Hegde (2010) note that computer display height, viewing distance and tilt angle are known to influence users' body discomfort and eye fatigue. They cite previous research that demonstrates user discomfort and neck and upper extremity muscle activities increase as the display is moved from user-preferred positions, noting that the previous studies were conducted using monitors with diagonal viewing dimensions of 19 inches or less. This study was conducted to investigate user positioning preferences for monitors greater than 19 inches, or for landscape dual display arrangements, situations that are increasingly common among user populations.
Although this study has limitations, which are noted below, the results are of interest. The primary findings include:
- The average preferred viewing distance increased as the size of the monitor increased;
- The average viewing distance for a single 27.5 inch display was significantly greater than that for a 19 inch display;
- The viewing distances for a 19 inch single display were not significantly different than that for a dual 19 inch display arrangement;
- The average viewing distance across all participants ranged from 26.8 to 29.9 inches;
- The viewing angle between eye horizontal and the top of the viewable portion of the display ranged between 0.0 and 2.2 degrees above eye height, with no significant differences between the different setups;
- The average downward viewing angle to the center of the display was 13.1 degrees, with no significant differences between the different setups;
- The viewing angle to the bottom of the viewable portion of the display ranged from 25 to 27.5 degrees below eye height, with an increasing trend as the size of the display increased, and a significant difference between the 19 and 27.5 inch displays;
- Participants tilted the top of the monitor back (i.e. the top of the display was slightly farther from the eyes than the bottom), with the larger displays being tilted less (5.1 to 5.4 degrees) than the 19 inch display (7.7 to 7.9 degrees), a statistically significant difference;
- Regardless of display size, participants set their keyboard height at or near elbow height;
- There were no significant differences in productivity or error rates between the conditions,
- There were no significant differences in body discomfort or visual acuity ratings between the conditions.
Shin and Hegde summarize their findings as follows:
Participants placed larger displays farther and lower while maintaining the display top at or near eye height. Preferred position of the dual displays in landscape setting did not differ from that of a single display. It appears that the preferred display position varies with the vertical dimension of the overall viewable area of the display.
The researchers tested four different display conditions:
- a 19 inch display;
- a 24.5 inch display;
- a 27 inch display; and
- dual 19 inch displays in a landscape (side-by-side) arrangement.
They used the following methods:
- 19 subjects participated in the study;
- Each was randomly exposed to all four setups, 20 minutes each, in a single experimental session that lasted 2.5 hrs;
- Participants had visual acuity between 20/15 and 20/30 with or without corrective lenses;
- All were healthy (7 females with an average age of 27.1 yrs, 12 males, with an average age of 24.9 yrs), with at least 1 yr of experience with office software applications, and all were touch typists;
- Character heights were set at 3.2 mm (equivalent to 12 point font, Times New Roman in Microsoft Office applications) for all conditions;
- All characters were black; the background was white;
- An adjustable computer workstation was used, including articulated monitor arms (adjustable in height, depth (described as horizontal by the authors) and fore-aft tilt), multi-adjustment chair (seat height and depth, armrest height and width, full sized backrest fixed at an angle of 109 degrees), articulated keyboard tray with height and depth;
- Participants were trained with regard to the adjustments, and the adjustment ranges afforded by the equipment allowed all subjects to achieve their preferred settings;
- A simple data entry task requiring participants to selectively transcribe (described as copying by the authors) text from one window to another, with the windows being set to occupy the entire available screen area;
- Participants were allowed to adjust workstation settings every 3 mins;
- Measurements were taken at four different time periods in the trials: 0, 5, 10, and 20 mins
- A 5 min break was provided between experimental conditions, at which time all adjustments were set to baseline settings;
- After each data entry task, participant’s visual acuity and subjective discomforts of eye, neck, shoulder, upper and lower arms, midback, and lower back were assessed to identify any fatigue or discomfort carryover effects from condition to condition;
- Productivity and error rates were also recorded for each condition.
The results of this study may or may not translate well beyond the conditions of this study. For example, older users, users with worse visual acuity, displays with smaller font settings or character contrast or color combinations, different task requirements, different work-rest cycles and task durations could all effect the these findings.
The Bottom Line — How this Applies to Ergonomists
Standards like ANSI/HFES 100-2007 Human Factors Engineering of Computer Workstations are based on data that precedes the onset of contemporary, larger flat screen displays and dual or multi monitor arrangements, which are becoming common. Fortunately, ANSI requires that such standards be re-affirmed or revised every 5 years, and that process is getting under way for ANSI/HFES 100. This study, and hopefully more like it to follow, will undoubtedly play a role in that update process. In the mean time, ergonomists now have evidence based opportunities to improve the set-up for larger displays and dual displays. Remember that this study looked at user preferred and user controlled settings, and proceed with caution in any attempts to use this new research as a "must do" approach to workstation set-up. Instead, it seems its best use is in justifying workstation design and equipment that provides a wide range of user controlled adjustments. With flexible/adjustable workstation design and training, users will be free — and armed with the knowledge — to setup their own work area to best support their own bodies, abilities and tasks.
Shin, Gwanseob; Hegde, Sudeep. User-Preferred Position of Computer Displays: Effects of Display Size. Human Factors, Volume 52, Number 5, October 2010 , pp. 574-585(12). doi: 10.1177/0018720810380405