Display location
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Display location
The location and orientation of the visual display terminal depend on the lighting characteristics of the work area, the viewing distance and angle, task sequence and glare control.
The requirements in ISO 9241 Part relate to a minimum design viewing distance:
"For usual office tasks, the design viewing distance shall be no less than 400 mm." (about 16 inches).
Character size determines both the minimum and maximum distance between the screen and the user's eye. In practice, many users prefer a viewing distance of between 35 and 50 cm,
or even longer if large characters are displayed. The greater distance is recommended as it will lessen the probability of visual discomfort since it requires less convergence likely to
cause eyestrain.
Proper display height is related to eye position. A comfortable line of sight is 10 degrees or more below the horizontal. The display screen itself subtends a large angle with respect to the
eye position. Hence, the display should be located so that the normal line of vision falls in the upper half of the display.
The tilt angle of a display should consider the trade-off between reduction in the angular size of the symbols and glare, or reflections from the surface of the display. The first several degrees
of tilt away from a plane normal to the line of sight has a minor affect on the angular size of the characters, as can be seen in the following, but may have a significant effect on glare.
| Screen surface orientation in degrees away from a plane normal to the line of sight |
Percent reduction of the angular height of the symbol |
| 5 |
0 |
| 10 |
2 |
| 15 |
3 |
| 20 |
6 |
| 25 |
9 |
Direct reflections from overhead light sources on the surface of the display may be annoying. This may happen even with displays that use an anti-glare treatment. As the display inclination is brought
forward, the probability of annoying specular reflections from overhead light is reduced. If the screen is located near the vertical and below eye height, specular reflections from overhead light should
not reach the eye at all.
In the course of a day's activities, people assume many different postures. Many slouch forward, some cross their legs, sit on one leg, or lean backward in their chairs. Shifting one's posture
periodically seems to be a natural and necessary activity whether at work, play, or even rest. Furniture, therefore, needs to provide clearances sufficient to accommodate postural flexibility. The space
under work surfaces is of particular importance, and BSR/HFES 100 Draft Standard (Human Factors Engineering of Computer Workstations) discusses that subject in great detail. Values are given for
the knee space under a work surface required for comfortable seating users ranging from 5th percentile females to 95th percentile males. The depth from the user's edge of a work surface is 44.0 cm
(17.3 inches) at the knee level. At the floor level the depth is given is as 60.0 cm (23.5 inches). The width is 52.0 cm (20.5 inches) and the height of the clearance envelope ranges between 50.0 to 69.0 cm
( 20.0 to 27 inches) measured from the bottom of the support surface to the floor.
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