VDTs and vision
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Introduction
A properly designed workstation is essential to an
employee's comfort, job satisfaction, motivation,
and a sense of accomplishment. This is particularly
true of the visual display terminal that plays such
a prominent role in so many workstations. There has
been concern about the possibility of ill effects
on the display user's eyes, but there is no evidence
that the human eye is damaged by the light levels
and visual tasks of a typical office environment.
For further discussion on this topic, the reader
is referred to the section on Luminance
Balance.
Workstation aspects
Some general considerations are important to mention. Most visual
display users prefer a viewing distance of 50-66 centimeters (20-26
inches) from the eye to the screen, or more, 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. Appropriate screen location depends on
eye position and line of sight. Since the most comfortable line
of sight is at least ten degrees below horizontal, the normal line
of vision should be from the eye to the top of the screen.
Of course, adjustment should be made for situations in which the
format of material dictates prolonged or repetitive concentration
on limited areas of the display screen.
The user may focus on the display screen, the keyboard,
documents at desktop level, or documents on document
holders that are at screen
height and viewing distance. When complaints exist, users should
be encouraged to speak with management to see if the
workstation
can be improved. Users who consult a vision care specialist should
be able to provide information on their workstation
design dimensions
and glare conditions. Figure 49 shows a typical VDT workstation
and some of the significant factors that can contribute
to user comfort.
Lighting, Reflection, and Glare
The display screen may reflect light from overhead lights, task
lights, light from windows, or clothing of a light color. The reflections
and the resultant glare can increase the difficulty of visual work.
The user's age should also be considered in problems of glare since
age affects eyesight in general, and glare sensitivity in particular.
Glare can usually be modified by lowering ambient
light, drawing window covers against bright light, wearing
less reflective garments, choosing more appropriate
task lighting, and cleaning the display screen. Keeping
the display screen clean, especially during conditions
of low humidity (e.g., in the winter with central heating),
is important as this decreases screen dust. Additionally,
neutral-density or micromesh filters may be helpful
in enhancing contrast or reducing glare.
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