Elsevier

Displays

Volume 42, April 2016, Pages 9-18
Displays

Visual ergonomics of video-display-terminal workstations: Field measurements of luminance for various display settings

https://doi.org/10.1016/j.displa.2016.02.001Get rights and content

Highlights

  • We have analyzed the International Standards on ergonomics of human–system interaction.

  • We have assessed luminance conditions of displays through in-field measurements.

  • Displays were rated on 14 different Contrast–Brightness combinations.

  • Displays have met the requirements only for some Contrast–Brightness combinations.

  • Analysis has shown the importance of a rapid assessment of display performance.

Abstract

Electronic visual displays have shown a rapid technological evolution in the last two decades. With reference to the ergonomic requirements for video display terminal (VDT) workstations (ISO 9241), at an international level, attention is focused on the human–system interaction. With reference to visual ergonomics, the aim of this study is to assess luminance conditions through in-field measurements in order to evaluate: luminance and contrast ratios, luminance and contrast non-uniformities. The assessment was applied to widespread flat screen displays and repeated for fourteen combinations of Contrast–Brightness. The analysis carried out by the Authors shows the importance of realizing a simple and quick procedure to determine the performance levels of displays used in VDT workstations. The proposed assessment could be used as a practical tool for staff assigned to assess the risks arising from VDT use in the workplace within the Occupational Health and Safety Assessment Procedure.

Introduction

The introduction of computers has led to dramatic changes in work practices for many people. Today, activities such as reading, writing, and typing can be carried out without moving from a computer. This change in work practices has been accompanied by an increase in complaints about a number of health problems associated with working at video display terminals (VDT) [1]. Eye discomforts and also hand/wrist problems are often associated with VDT work. Results of different studies suggest that VDT users have increased the risk of developing eye discomforts, musculoskeletal pains and mental load [2], [3], [4], [5], [6], [7]. As the work force becomes more and more dependent on computers, the need for proper and efficient design of VDT workstations [8] and also the need for risk assessment procedures [9] become increasingly critical.

With special reference to visual ergonomics, the main device of the VDT workstation is the monitor, because it represents the primary object of vision. The task of the monitor is to reproduce information; the quality of the information reproduced can sometimes be crucial for properly carrying out work tasks, especially if particular workstations are considered such as those used in mission critical control rooms (i.e. control rooms in airports, police stations, civil protection units,…).

As a visual object, a monitor is substantially different from a sheet of paper in many ways and viewing a monitor is much more visually demanding than viewing paper [10]. Unlike paper, a self-illuminated monitor, which is refreshed at a certain rate, and consists of different combinations of background and foreground causing different contrasting color objects that influence visual fatigue and can contribute to the outbreak of the Computer Vision Syndrome [11], [12], [13], [14]. The objects displayed on a monitor consist of a series of pixel-based dots with decreasing brightness on their outer edges, thus making it hard for the eyes to focus. In addition, the viewing distance between the eyes and the computer screen is important and often not easily adjusted, especially if compared with the simple movement of a book to adjust viewing distance [12], [14], [15], [16], [17], [18].

Monitors have undergone a rapid technological development and over the past 20–30 years we have gone from CRT phosphor monochrome displays to CRT color displays and then from LCD displays to the current LED displays. This evolution has resulted in an increase in the resolution and consequently in an improvement of visual performance and visual comfort as demonstrated by Ziefle [19]. Although displays realized with these new technologies can be considered photobiological risk exempt, as demonstrated by the extensive studies on the equipments commonly used in office workplaces [20], [21], [22], [23], [24], their effects on visual fatigue are still under investigation.

To obtain good visual performance while working at a VDT it is very important that luminance contrast and screen luminance are appropriate. Luminance contrast is an important factor in visual performance and display quality: the effect of luminance contrast on visual acuity and on the perception of the worker is huge, as shown in [25], [26], [27], [28], [29]. A significant improvement in both visual acuity and visual comfort can be obtained by increasing the luminance contrast, however this contrast must not exceed the value of 8:1, above which comfort falls again [8].

Section snippets

Requirements for electronic visual displays: International Standards

Electronic visual displays have had an extremely rapid technological evolution in the last two decades. They have reached increasingly higher performance levels and have changed the way that work is carried out in numerous professional jobs. For this reason, recently, with particular reference to those professional activities which require particular visual tasks (or time prolonged tasks) and high levels of precision, the need was felt to standardize the parameters to be evaluated in order to

Display luminance

In this paper the Authors are particularly concerned with the analysis of luminance through in-field measurements in order to evaluate the following requisites: luminance ratio, contrast ratio, luminance non-uniformity and contrast non-uniformity. For this reason, together with a specific analysis of the display itself, it is necessary to conduct a simultaneous analysis of the workstation’s detailed lighting (i.e. the desk) and, more in general, the lighting of the work environment (i.e. the

Field measurements of luminance displays

EN ISO 9241-306 defines the field assessment criteria of requisites introduced in EN ISO 9241-303 (see Table 1). The measurements of luminance on the display surface, according to what is foreseen in EN ISO 9241-306, must be carried out by measuring the luminance in predefined positions (see Fig. 1) both with a model having white targets on a black background and with a model having black targets on a white background. The measurements must be carried out by placing the luminance meter probe

Conclusive remarks

Electronic visual displays have had an extremely rapid technological evolution in the last two decades. They have reached increasingly higher performance levels and have changed the way that work is carried out in numerous professional jobs. With reference to the ergonomic requirements for office work with visual display terminals (EN ISO 9241 series), at an international level the attention is focused on the human–system interaction. In order to satisfy the human–system interaction, different

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