- The optimum monitor height is different in different countries. In the USA, Great Britain, Belgium and the Netherlands (e.g. AI2), the norms and guidelines most commonly advise setting the upper side of the monitor at or just under eye level. In Scandinavian countries and Germany, placing the monitor lower is more usual. International norms also assume a lower monitor position (ISO 9241-5).
Our advice in this regard is to place the middle of the monitor at between 17.5° and 35° under eye height. This is based on an optimum balance between comfort, physical stress and productivity (Sommerich, 1998), where the optimum also depends on whether the user can type blind or not and his/her sitting posture.
To determine the optimum height, we must first determine what the eye height is. The monitor is then placed at or just under the eye height. For P90 (tallest 5% to the shortest 5% of the population) the eye height from the desk is between 48.6 cm and 61.4 cm (Dined, 2004). To place the monitor at eye height, a positioning range of between 48.6 and 61.4 cm, measured from the desk to the upper side of the monitor, is needed. To realise a viewing angle relative to the middle of the monitor of 17.5° and 35°, one must be able to place the monitor lower and so a larger range is therefore needed. A rule of thumb is therefore a range of 35-59 cm.
Council Directive 90/270/EEC
According to the Council Directive 90/270/EEC, article 9, employers must provide employees with the opportunity to have an eye examination upon commencing work and at regular intervals or in the case of eye problems. If this examination shows that monitor glasses are needed, the employer must pay the costs of this.
Minimum requirements for monitor workstations are stipulated in the Annex to the abovementioned norm:
Article 1.b of the Council Directive states that monitors must be freely movable and easy to adjust and tiltable. This can be achieved by, for example, mounting the monitor on a flat screen arm. The monitor may not form a whole with the keyboard (as is the case with laptops). This can be solved by using a separate monitor and keyboard + mouse possibly in combination with a docking station or by using a laptop holder in combination with a keyboard + mouse.
Article 2 contains guidelines regarding the organisation of monitor workstations. Reflections on the screen must be avoided, suitable sunshades must be used and the equipment must not cause an annoying noise or heat.
- Auswirkungen auf die Gesundheit
- Viewing distance
A relatively large viewing distance is less tiring on the eyes, because one’s eyes do not have to accommodate so hard. A condition for this is that the characters on the screen are all the same size (Owens and Wolf Kelly, 1987). The characters on the screen can sometimes be enlarged. Word has a zoom in and out function that can be used to increase or decrease the size of the active document.
A monitor position with a viewing angle of the eyes to the screen of between 20° and 50° allows the eyes to better accommodate (Ripple, 1952) and converge (Krimsky, 1948), and the overall strain on the eyes is reduced (Tyrell and Leibowitz, 1990, Tsubota and Nakamori, 1993). In addition, this monitor position results in fewer neck ailments and complaints (Kumar 1994; McKinnon 1994, Marcus 2002), while this does not result in a static stress on the neck muscles (Turville et al., 1998).
- Auswirkungen auf die Leistungen
- Viewing distance
Jaschinski-Kruza (1988) compared productivity at a viewing distance of 50 centimetres with productivity at a viewing distance of 100 centimetres. Jaschinski-Kruza found increased productivity with the long viewing distance where the characters were twice as large for the long viewing distance. To maintain this productivity advantage one must increase the viewing distance, but at the same time increase the size of the characters.
Sommerich researched productivity in relation to the viewing angle (Sommerich et al., 1998). He found 10%-higher productivity when the middle of the monitor was placed 35° under the eye height (the test subject had to compare a column with references on the right side of the screen with a column on the left side of the screen and correct the differences, the number of references that were changed was a measure of the productivity).
Dual or Multi-screen
Large monitors, 22” or more, can be divided into two, thereby creating a dualscreen solution. An increasing number of computer users work with two or more applications at the same time, where information from one application can be compared with that of another, or which must be copied from one to the other. In these cases, displaying both applications alongside each other is easier and much more efficient. Scientific research has shown that with specific tasks 33% fewer mistakes are made and productivity is at least 11% higher (Colvin, 2004).
Choosing a widescreen monitor which displays dualscreen or two separate monitors beside each other depends on the type of task that must be performed. In principle, more can be displayed on two separate monitors than on a widescreen. The table below shows how much information fits on a screen:
Screen size 2 x 17" screen 2 x 19" screen 2 x 21" screen 22" widescreen 24" widescreen Quantity of information in number of pixels 2,621,440 2,621,440 3,840,000 1,764,000 2,304,000
- Choosing a monitor
The specifications of monitors have greatly improved in recent years, such that the differences have become minor. In other words, the image quality can be called good on most screens. The distinguishing features:
• Contrast value (for normal use a standard contrast of 450 : 1 (number of grey tints) is adequate, a higher value is recommended for the sharp display of colours).
• Resolution (measured in pixel density, the higher the resolution, the more information that can be displayed). When using a relatively small (laptop) screen with a very high resolution, the letters and icons are displayed relatively small. The advantage of this is that you can display a lot of information on a small screen, but it reduces legibility and you have to read the screen from very close by to read it easily. This clearly puts more strain on one’s eyes.
• Brightness (under normal light conditions, 250 cd/m2 is enough; when extra brightness is needed, e.g. when working outside or in brightly-lit conditions, 350 cd/m2 or is recommended).
• Energy consumption (20-35 W is relatively low; also look at the energy star label).
Screens with a glossy surface are increasingly used, especially in laptops. The advantage of such screens is that the contrast is better and the colours are clearer. This is important when viewing films (at home), but it is not ergonomically recommended because this creates reflections on the screen.
Choosing a monitor arm
When choosing a monitor arm, you can use the following comparison criteria.
Comparison criteria Comparison criteria Description Height range A flat screen arm must allow one to adjust one’s monitor to the right height. The ideal monitor height greatly depends on a number of factors: task type (non-blind typing, blind typing, mouse work) and one’s sitting posture. If the user tends to lean backwards, the monitor must clearly be placed higher. If the user tends to lean forwards (e.g. when not typing blind), the monitor must be placed much lower. One should therefore be able to set the upper side of the monitor to approximately 30 cm (monitor on desk) above eye height (for tall people 58 cm). Depth range The flat screen arm must have a good depth setting. We recommend a viewing distance of 50 - 70 cm, preferably a relatively large viewing distance of approximately 70 cm where the character size is also big. However, a shorter viewing distance is recommended when the characters are relatively small. The depth of most desks is between 80 cm and 100 cm (for frequently used corner setups of 120x120x80x80, the depth is also 100 cm). This means that the arm must bridge a distance of 10 to 50 or 60 cm. Rear tilting To realise a correct viewing angle, it is important that one can tilt the monitor backwards sufficiently. The lower the monitor is placed, the more the monitor must be tilted backwards. The viewing angle (the viewing angle is the uppermost angle between the viewing line, the line from the eye to the screen, and the monitor), must be a bit more than 90 degrees. Landscape (L) Rotating (R) Sideward’s rotating of the monitor was developed to allow a second person (e.g. a colleague or a customer) to also view the screen (minimum 60° rotation must be possible for this).
The Landscape function allows one to turn the screen 90° so that the user can view a whole A4 on the screen; this is particularly useful when using Word.
Ease of adjustment Being able to quickly and easily adjust the position of a monitor is important. The ideal monitor position depends on, among other things, the type of tasks that are performed and on the chosen sitting posture. Because tasks and sitting posture change regularly, changing the height, depth and angle of the monitor quickly and easily must also be possible. This can best be achieved using a gas-sprung flat screen arm. Cable management The monitor cables must be arranged properly without obstructing the flat screen arm movement. Load bearing limit Most monitors way between 3.5 kg and maximum 8 kg.
- • Dataset 'Nederlandse volwassenen', Populatie 'DINED 2004 (20-30 jaar)' (Dataset 'Dutch Adults', Population 'DINED 2004 (20-30 years)' :
• Council Directive 90/270/EEC of 29 May 1990 on the minimum safety and health requirements for work with display screen equipment (fifth individual Directive within the meaning of Article 16 (1) of Directive 89/391/EEC) http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:31990L0270:EN:HTML
• AI-2 Werken met beeldschermen, Arbo Informatieblad van het Ministerie van SZW, Sdu Uitgevers, Den Haag, ISBN: 90 12 10641 9 (AI-2 Working with monitors, Working Conditions Information Sheet of the Dutch Ministry of Social Affairs and Employment, Sdu Publishers, The Hague, ISBN: 90 12 10641 9)
• ISO 9241-5:1998 Ergonomic requirements for office work with visual display terminals (VDTs) -- Part 5: Workstation layout and postural requirements
• Sommerich, C.M., Joines, M.B., and Psihogios, J.P., Effects of VDT Viewing on User Biomechanics, Comfort, and Preference. Proceedings of the Human Factors Society 42nd Annual Meeting, 1998, 861-865
• C. Owens, D.A. and Wolf-Kelly, K. (1987). Near Work, Visual Fatigue, and Variations of Oculomotor Tonus. Investigative Ophthalmology and Visual Science. 28, 743-749
• Ripple, P., Variation of Accommodation in Vertical Directions of Gaze. American Journal of Ophthalmology, 35, 1952, 1630-1634
• Krimsky, E., The Management of Binocular Imbalance. Philadelphia: Lea and Febiger, 1948
• Tyrrell, R. and Leibowitz, H., The Relation of Vergence Effort to Reports of Visual Fatigue Following Prolonged Near Work. Human Factors, 32, 3, 1990, 341-357
• Tsubota, K., Nakamori, K., Dry Eyes and Video Display Terminal. New England Journal of Medicine, 328, 8, 1993, 584
• Kumar, R., Study of stress injury when using pointing devices, Industrial Ergonomics, Department of Human Work Sciences, Luleå Technical University, 2002
• Mackinnon, S.E., Novak, C.B., Clinical commentary: Pathogenesis of Cumulative Trauma Disorder. Journal of Hand Surgery. 19A, 5, 1994, 873-883
• Marcus M, Gerr F, Monteilh C, Ortiz DJ, Gentry E, Cohen S, Edwards A, Ensor C, Kleinbaum D. A Prospective study of computer users: II. Postural risk factors for musculoskeletal symptoms and disorders. Am J Ind Med 2002, 41, pages 236-249
• Turville, K.L., Psihogios, J.P., Ulmer, T.R. and Mirka, G.A., The effects of video display terminal height on the operator: a comparison of the 15° and 40° recommendations. Applied Ergonomics, 1998, 29, 4, pages 239-246