Does the position of a computer monitor effect your health?
The position of a computer monitor can have very significant effect
on the well being of the user, and can make a major impact on productivity,
eye strain, stress and other postural induced conditions such as neck
and back aches. This note provides information that should help reduce
fatigue, headaches and a wide range of symptoms caused by using incorrectly
positioned computer screens.
Most modern monitor (e.g. post 1997) provide good quality resolution
and lower emissions (e.g. MRPII standards). However, factors such
as ambient lighting, the user's eye to screen distance, and the angle
at which it is viewed can make big differences.
A monitor at eye level means a more rigid upright position, whereas
a lower monitor allows for a more varied neck position, and better
long-term back health.
The monitor is best read at an angle such that the top of the monitor
is slightly further away than the bottom, similar to how a newspaper
is often read.
The comfortable viewing angle is between 15 and 50 degrees below
eye level, this fact was recognised by ISO (International Standards
Organisation) in 1998 (ISO 9241-5). A lower angle reduces the total
amount of eye exposed to the atmosphere and therefore decreases tear
evaporation. This reduces any Dry Eye syndrome, especially for blue-eyed
people who normally have dryer eyes.
The natural focal distance (point of convergence) for the eyes is
around 114cm (45 inches, 3ft 9in) straight ahead or 89cm (35 inches,
2ft 11 ins) when viewed at a 30 degree downward angle. Anything less
than this can cause eyestrain leading to discomfort and possible headaches.
The monitor should not be less than 30cm (12 inches) away. Tests show
that the productive distance is 102cm (3ft 4in). Viewing at longer
distances means that the text/image size may need to be increased,
or that larger screen sizes (e.g. 19 or 21 inch) should be used.
Previously it was common practice to mount monitors on top of desktop
PC units, or use mechanical arms to position the monitor close to
eye level. This was based on the idea that this elevation was the
eye's natural position at rest. It is not good practice for the monitor
to be at eye level, or to be vertical to the face.
To prevent eyes from focusing at a fixed distance for too long they
should be refocused, at least every 15 minutes, by looking at far-away
objects. It is easy to become engrossed and lose track of time, so
some programs are available which are activated after set periods
of activity. These alert you to divert your gaze. Moving you limbs
head and neck will help prevent muscles being 'locked' in a fixed
position.
Use of computer monitor screens in the UK is covered by legislation
which provides for the employer to provide eyesight testing and glasses
if required.
Lighting is also important, especially with larger screens. The glass
will always cause a reflection. Bright downward facing ceiling lights
are not recommended. Cheaper and certainly older Fluorescent lighting
can also be seen to flicker since they emit pulses of light 100 times
per second, (i.e. in the UK at twice the mains frequency of 50 Hz).
Fluorescent lights using electronic ballasts offer a much smoother
light. The best form of lighting is upward facing, which gives a more
diffused light caused by being reflected off the ceiling.
More Information is available from the following links:
www.ccohs.ca/oshanswers/ergonomics/office/
www.office-ergo.com/setting.htm
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