Work Station Design For VDU Operators: Part I

Photo credit: eye2eye-cardiff-opticians.co.uk

Factors to be considered in work station design are: lighting, glare, flicker, color contrast, alpha-numeric design and ergonomics.

Lighting

The correct level of illumination is essential for a comfortable and efficient visual performance. Several investigators have suggested that illumination and its effects on the VDU are a possible cause of the high rate of asthenopic symptoms amongst the operators.

A high level of illumination will improve the legibility of the script when there are dark characters on a light background but the reverse occurs for a display with light characters on a dark screen. Therefore, an optimum level of illumination is required to ensure that the legibility of the script and screen characters is least impaired.

Older VDU operators will require a higher level of illumination, which can be provided by local lighting but must be shielded from other operators or it will act as a glare source. In general, ambient lighting should provide about two-thirds of the required illuminance and local lighting of the work station should provide the rest. The lighting needs to be designed to avoid direct and reflected glare and this can be achieved by direct lighting from low luminance down-ward-pointing luminaires by direct lighting from uplighters or by a combination of two systems.

When using uplighters, the ceiling is used as a large area of low luminance. This overcomes any problems of glare; any reflections from the VDU screen will be of low luminance. Uplighters can be free floor-standing, furniture-mounted, wall-mounted or suspended and ideally, they should be used where the ceiling height is at least 2.5m.

Glare

Glare is one of main complaints made by VDU operators and is caused by bright sources of light falling within the operator's field of vision. There are two types of glare: disability glare and discomfort glare. The former impairs the ability to see detail without necessarily causing visual discomfort and the latter causes visual discomfort without impairing the ability to see detail. To avoid discomfort glare, a glare index of 19 is recommended for general office work.

Recommended: Glare and its control 

Glare may arise from direct light or indirectly from reflections. Direct glare is most frequently caused by the light from a window or an artificial light source that is too large or too bright. Other causes of glare are reflections from shiny, even surfaces such as gloss-painted walls, linoleum covered floor, polished wooden furniture, etc. Light may be reflected from the VDU itself from the screen or the keyboard. Reflectances from the surface of the VDU screen can be very annoying. Screens are often slightly convex and act as a mirror, reflecting whatever is in front of the screen, e.g. the operator or light sources. The concave keys can also reflect light into the operator eyes.

There are several methods of reducing or eliminating glare sources:

1. Adjust the position of the VDU screen so that the operator cannot see any reflections from the screen or other polished surfaces. 
2. Change the position of troublesome light sources where possible. 
3. Fit light sources with the appropriate diffusers.
4.  Fluorescent light fittings, if used, should be positioned with their length parallel to the side of the VDU. 
5. The screen should be non-reflective and designed so that it can be tilted or rotated. 
6. The keyboard should have a matt surround and the keys should have low reflectance surfaces. 
7. Matt scripts should be used, preferably in pastel colors. 
8. Use a light-colored desk top in preference to a dark one. 
9. The legibility of the characters on the screen can be altered by adjusting the contrast and brightness controls of the VDU.
10.  Windows should be fitted with blinds e.g. vertical louvred blinds.

The following methods are used to eliminate the screen reflections:

Filter panels, polarization filters, micromesh filter, etching the glass screen, anti-reflection coats and tube shields.

The best method of providing an anti-reflection coating without losing the clarity of the characters is by the vacuum deposition of a thin film layer with a thickness of 0.25 the wavelength of light. This technique is effective but expensive, as the coating is applied to a glass panel which is then bonded to the screen surface. It is also very sensitive to dust and dirt and shows up finger prints. Therefore, if the filter surface is not cleaned regularly the characters will appear to be smeared.

Proceed to: Part II