Transcript ارگونومی بصری کامپیوتر

‫ارگونومی بصری کامپیوتر‬
‫آیدین تاج زاده نمین ‪81189803‬‬
‫حمیدرضا حافظ نیا ‪81190003‬‬
‫‪1‬‬
‫اردیبهشت ‪1385‬‬
How do you setup a Computer
WorkStation?






Do you buy monitor risers?
Will even lower monitor positions
cause neck strain?
Should you invest in indirect lighting?
How about viewing distance? 16”,
25” or even farther?
Does screen color make a
difference?
Is there any evidence that ergonomic
workstations improve work
performance?
2
The Most Common Refractive
Errors




Hyperopia
Myopia
Presbyopia
Eye Strain :







Burning
Tightness
Sharp pains
Watering
Blurring
Double Vision
Headache
3
Hyperopia
4
Myopia
5
Presbyopia
6
A Dozen Things You Should
Know about Eyestrain
1- Definition: If you have any eye discomfort caused by
viewing something, you can call it eyestrain.
2- In Visual Display Terminal (VDT) workstations, the
principal factors affecting the ability to see well are:

Glare
•
the luminance (brightness) difference between what is
being looked at and its immediate environment
•
The amount of Light
•
The distance between eye , screen and document
•
The readability of screen and documents
•
The worker’s vision and his/her corrective lenses
7
A Dozen Things You Should
Know about Eyestrain
3. Watch out for direct glare.
4. Reflected glare, such as on computer screens, sometimes causes
eyestrain.
5. The most overlooked cause of eyestrain in offices is contrast --usually, a dark screen surrounded by a bright background such
as a window or a lit wall.
6. The amount of needed light depends on your age, the quality of
the print you're reading, and other factors.
7. Eyes are strained more by close viewing than by distant viewing.
8. If you gaze at something too long, your eyes can tire.(20/20 Rule.)
9. If two objects are only a couple of inches different in their distance
from the eyes, the eyes actually do NOT have to refocus to look
from one to another.
10. Computer work cause nearsightedness.
11. Sometimes eyestrain is just a case of dry eyes.
12. People who need bifocals should consider other options besides
bifocals.
8
Visual Factors






Visual Acuity
Binocular Vision
Accommodation
Oculomotor Skills
Hyperphoria
Dry Eyes
9
Definitions



Visual acuity
Brightness & Contrast
Display Quality
Refresh Rate
 Resolution
 Dot Pitch

10
Resolution
11
Refresh Rate
12
Guidelines: Screen Colors
 Screen colors: dark letters on a light
background.
 With the monitor off, look at your
reflection in the screen. Now turn the
monitor on and select a Windowstype background, (black letters on a
white background). Notice that you
cannot see your reflection as well.
 Negative screen contrast (black
letters/white background) can reduce
reflected images .
13
Guidelines: Screen Colors

Research
Bauer and Cavonius (1980) found a lower error rate, with
dark letters on a white background. Snyder and his
colleagues (1990) also compared black and white
backgrounds. Eight out of ten subjects increased their
performance by using dark letters on a light background.
The improvements ranged from a low of 2.0% to a high of
31.6%. The tasks were visual search and reliable.
14
Guidelines: Vertical Monitor Location
 Locate the entire viewing area of the monitor
between 15° and 50° below horizontal eye level.
15
Guidelines: Vertical Monitor Location
To see the effect of gaze angle on
accommodation you can this exercise
1. hold a business card at arm's length and
at eye level.
2. Slowly bring it towards you until the letters
start to blur.
3. Without moving your head, slowly lower the
card in an arc, keeping it the same
distance from your eyes
4. You will see the letters come into focus.
Your eyes have improved their ability to
accommodate simply by lowering their
gaze angle
16
Guidelines: Vertical Monitor Location


The old guidelines that recommended that
the monitor be placed at eye level were
based in part on the belief that the resting
position of the eyes is 15° below the
horizontal .
New evidence shows that, while the eyes
might be most comfortable with a 15° gaze
angle when looking at distant objects, for
close objects they prefer a much more
downward gaze angle .optimum position
for the most important visual display is 20 50° below the horizontal line of sight.
(according to the International Standards
Organization-ISO)
17
Guidelines: Vertical Monitor Location
18
Guidelines: Vertical Monitor Location

Many computer users experience dry eyes.
It has been found that lower monitor
placement exposes less of the eyeball to
the atmosphere and reduces the rate of
tear evaporation. This keeps the eyes more
moist and reduces the risk of Dry Eye
Syndrome.
19
Guidelines: Vertical Monitor Location

Neck Posture

Neck extension and forward head posture, while
acceptable for the visual system, have been associated
.
with both discomfort and disease


With a low monitor position you can hold your head erect
and look downward. When that posture becomes tiring, a
low monitor will allow you to alternate among a wide
range of flexed neck postures that allow good visual
performance and will not increase postural discomfort.
Ergonomic guidelines recommend arms, torso, thighs and
legs at 90° angles and the head perfectly erect,the feet
are "flat on the floor." This is the "correct posture”.
20
Guidelines: Vertical Monitor Location

1.
Neck Posture (Cont’d)
Two recent studies have compared monitor locations
with the center of the screen at 15° and 40° below
horizontal.
The first one the recommended limit for mean muscle
activity is 10-14% maximum voluntary contraction
(MVC) (MVC is the maximum muscle effort that can be
voluntary exerted by the subject.) Although the 40°
placement had higher readings than the 15°
placement, all were much lower than the
recommended limit. The highest was 6.8%. The activity
averaged an extremely low 2.2% MVC for the 15° and
2.0% MVC for the 40° conditions.
21
Guidelines: Vertical Monitor
Location
2 . The second compared monitor positions with the
center of the monitor at eye level, and 17.5° and 35°
below eye level. All of the conditions resulted in
mean EMG levels of below 4% MVC, well below the
recommended limit of 10-14%.
They found a 10% improvement in productivity
when the center of the monitor was changed from
eye level to 35° below eye level. Performance was
measured as the number of bibliographic references
the subjects were able to format in the allowed time.
22
Guidelines: Vertical Monitor Location
23
Guidelines: Placement




The screen should be at least 18 to 24 inches
distance. Adjust this distance for your visual acuity
needs and comfort. The farther away the better in
most cases. Distances of 30-40 inches are frequently
preferred.
You should be able to view the screen with a slight
downward gaze without tilting your head up or down.
The top of the screen should be about at midforehead level. If you have a screen larger than 17”,
the top of the screen may need to be a little higher.
Your face should be parallel to the screen. Setting the
tilt will help to adjust the height. Be sure to test for
excessive glare when tilting the screen. If you can see
your image in the screen, reflections and glare will
strain your eyes while working.
Your documents should be positioned close to the
monitor, either close to the side or directly in front
between the keyboard and the screen.
24
Guidelines: Brightness & Contarst

The monitor’s brightness should match the room
brightness. Begin making adjustments by reducing glare
from sources in the room such as windows and overhead
lights. Use light switches, blinds, curtains, filters or
remove bulbs as necessary. Then adjust the brightness
control on the monitor somewhere close to the monitor’s
mid-range if possible. After adjusting the brightness, set
the contrast to a comfortable level. Usually, the higher the
contrast the better.
25
Guidelines: Quality Display

The clarity of your screen depends upon refresh
rate, resolution and dot pitch.



Refresh rate refers to how often your monitor redraws
the screen. Slow rates can cause a noticeable flicker..
Your refresh rate should be at least 70 Hz (hertz) or
higher.
Resolution refers to the monitor’s pixel density and
determines the level of detail. The higher the
resolution, the better the detail. 800 x 600 is
recommended. Make sure you don’t sacrifice the
refresh rate for resolution. They are related to each
other and should both be high for good quality.
Dot pitch determines sharpness of the display. The
lower the dot pitch number, the sharper the image.
Select a monitor with a dot pitch or .28 mm
(millimeters) or lower. (If your dot pitch is listed as
horizontal or stripe pitch, divide it by 0.866 to
determine the equivalent regular dot pitch.)
26
Guidelines: Luminance

The Illuminating Engineering Society of North
America (IES), in its Recommended Practice for
Lighting Offices Containing Computer Visual
Display Terminals states that the average
luminance produced by direct lighting luminaires
should never exceed the following values:




850 cd/m2 at 65°
350 cd/m2 at 75°
175 cd/m2 at 85°
These recommendations cannot be properly
evaluated . for example, the ceiling luminance was
350 cd/m2 then the fixture would be invisible in any
screen at 75 because it has no contrast with the
ceiling. At 85°, it would have a contrast against the
ceiling of 33 percent. However, the contrast of the
reflection on a bright background display of 100
cd/m2 would be only 5.8 percent.
27
Guidelines: Luminance

It is suggested that the ratio of the ceiling luminance
directly above the normally the brightest area to the
ceiling illuminance between luminaires should never
exceed 10:1 and, preferably, this luminance ratio
should be limited to 4:1. The maximum luminance
on the ceiling should not exceed 850 cd/m 2 for any
area. Using the contrast equation presented in the
sidebar, the 850 cd/m 2 maximum luminance, the
preferred luminance ratio of 4:1, and assuming an 8
percent reflection from the screen, the contrast of
the luminous ceiling reflected in a bright-background
VDT display of 100 cd/m 2 will be 18 percent – well
in excess of the contrast threshold criteria of 2 and
5 percent.
28
Thanks For Listening…
Any Questions So far?!!!
29