Visual discomfort at a workstation occurs when the visual demands of the task exceed the visual abilities of the individual. The problem can be resolved by treating the visual condition and /or by making the visual task less demanding. A thorough eye examination is necessary to determine if there are any visual problems. The eye examination must include analysis of the functioning of the eyes at near working distances. It is also important that the computer worker provide the examining doctor with information about the computer viewing distance (from eyes to computer) and the location of the computer in the field of view.
Listed below are suggestions for improving the comfort of the computer workstation and environment. Most of these suggestions are for the improvement of visual comfort but some are related to posture or other forms of comfort.
Although the quantity of illumination is important, it is probably more important to have good light distribution. Good light distribution is accomplished when all of the objects in the field of view have approximately equal brightness. Bright lights or windows are common offending sources and cause discomfort. The worker can determine if the overhead lights or windows are contributing to discomfort by shielding them from the field of view with their hand or a file folder- simulating a visor. If a small but immediate sense of relief occurs, the bright source is contributing to discomfort. Suggestions for improving the lighting include:
1. Use blinds or drapes on windows in order to eliminate the bright light. It is often necessary to adjust the blinds during the day. They should be adjusted to allow light into the room without being able to see the bright light directly.
2. It is usually inadvisable to put additional lighting on reference documents- this makes them too bright compared to the screen.
3. If auxiliary desk lighting is used, it should usually be low wattage and should be directed so that it does not directly enter the eyes or directly illuminate the computer screen.
4. Indirect lighting systems often provide the best visual environment.
5. Wear a visor to shield eyes from bright overhead lights.
6. Reorient the workstation so that bright lights are not in the field of view.
7. Avoid white reflective surfaces. Desktops and other furnishings should have a matte, medium reflective surface.
8. Ceiling should be painted white and walls should be medium light.
9. Most offices have too much light- 75-150 foot candles. The recommendation for computer workstations is 18-46 foot candles. The lower recommendation for computers largely because the computer screen background is often dark. Higher light levels are OK with white background screen. Too much room illumination makes the room too bright compared to the computer, resulting in visual discomfort and too many screen reflections.
10. Turn off some fluorescent light fixtures which are in your field of view and are bothersome. Be considerate of the effects on other employees.
Reflections in the screen decrease the visibility of text on the screen by decreasing contrast. The worker can determine if this is a problem by temporarily using light baffles such as file folders to shield the screen from offending light sources. If this results in a noticeable increase in contrast and clarity of the test, then the reflections are a problem and should be addressed.
1. An anti-reflection screen can be placed over the computer. Glass screens perform better than mesh screens. Look for screens that have been approved by the American Optometric Association.
2. Eliminate the offending light sources. Windows and other bright lights behind you are the sources of the reflections.
3. Use dark characters on a light background, they are less affected by reflections than are light characters on a dark background.
4. A hood can be purchased and placed over the computer to shield it from offending sources. Hoods often don?t perform as well as anti-reflection screens.
VIDEO DISPLAY CHARACTERISTICS
1. Good screen resolution is important- especially for extended work. Screens with more pixels generally provide better resolution.
2. Black characters on a white background is probably the best. However, other combinations can be comfortable so long as the brightness contrast between the characters and the background is high. It is best to avoid dark backgrounds.
3. The size of the text should be three times the size of the smallest text you can read. You can test this by viewing the screen from 3 times your usual working distance- you should still be able to read the text.
4. Monochrome displays usually have better resolution than color monitors. If the job does not require color, it is often best to use a monochrome monitor.
5. Although 60 Hertz is the most common refresh rate, higher refresh rates (75 Hz or more) are preferred. (this applies to CRT monitors only)
6. For color monitors, small dot pitches (less than 0.28mm) are desirable.
7. Adjust the screen brightness and contrast so that character definition and resolution is maximized.
8. The screen brightness should be adjusted to match the general background brightness of the room. This is much easier to do with light background screens.
Some people experience a flickering sensation at a computer. If this is bothersome:
1. Turn down the brightness of the computer.
2. Use a dark background instead of a light background computer.
3. Obtain a computer with a higher refresh rate (we recommend a 75 MHz minimum).
WORKSTATION FURNITURE AND ARRANGEMENT
Traditionally, the "ideal" workstation posture is to have a right angle at the knees, a right angle at the hip joint, and a right angle at the elbows in order to reach the keyboard. Although this is represented as "ideal", many workers find optimum comfort in postures that deviate quite significantly from this one. Recent evidence indicates that the hip joint should be wider open than 90 degrees. It is probably most important that the worker change posture during that day so as not to remain in one rigid position. Easy adjustability of workstation furniture is most important. There is clear evidence to show that the eyes are most comfortable and productive when looking downward 10-20 degrees.
1. The table should allow for adjustability in keyboard height. The worker should not be reaching up to the keyboard. It is usually best for the keyboard to be 3-5 inches below the standard desktop height of 29 inches. It should also have adequate space for the computer and reference material and should provide adequate knee space.
2. The chair should be easily adjustable in height, should provide adjustable lower back support, and should have a flexible, woven seat covering. Five legs provide better stability than four. Full armrests are not recommended- they often preclude moving the chair under the table. However, support for the elbow or forearm can relieve strain on the shoulder, arms and wrists.
3. The height of the computer screen should be adjustable. The center of the screen should be 10-20 degrees below the straight ahead gaze of the worker- or 4-9 inches below the eyes for normal working distances. In most cases the top of the screen should be just below the eyes. If the screen is higher than these recommendations, it causes posture changes.
4. Reference documents should be located close to the screen with adjustable copy holders. If possible, the distance from the eyes to the reference documents should b e the same as to the computer. The brightness of reference documents should fairly match that of the computer screen- auxiliary reference document lighting usually makes reference documents too bright.
5. Shorter employees benefit from a foot rest.
6. Many employees find a wrist rest helpful. The wrists should be straight while typing. When typing, your wrists should "float" just above the wrist rest. The wrist rest is to rest upon- not to use while typing.