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2. Lighting – Computer Ergonomics

  • Content last reviewed: November 2010

When computer work environments are being planned, both overall lighting levels and the positioning of lights and windows must be considered.

Area lighting (overhead fixture) levels from 300 to 500 lux are generally considered to be the most appropriate for computer work. However, paper-based work often requires more light, particularly for poor quality or handwritten text. Older workers may also require more light. In these cases task lighting (small lamps for a specific area) can be used.

Excessive light levels may "mask" (or partly hide) characters or whatever is shown on the screen and create more and brighter sources of glare.

Glare is caused by large differences in light levels within the visual field. The eyes try to adapt to these large differences and visual fatigue and discomfort may result. In addition, the computer operator may adopt a poor posture while trying to reduce the glare by changing his or her orientation to the screen. This may result in neck and back pain.

There are three types of glare: direct, indirect and masking. Direct glare occurs when there are bright light sources directly in the operator's field of view. Windows are often a source of direct glare. Indirect glare occurs when light from windows or overhead lighting is reflected off shiny surfaces in the field of view, such as terminal screens, desks and other office equipment. Light from sources directly overhead causes masking glare on the screen, partly obscuring what the operator is trying to focus on.

Ways of reducing both direct and indirect glare include the use of light-absorbing blinds or curtains.

Methods used to control light from windows should allow for user control. Roller, vertical or venetian blinds, or thick curtains can be used. However, care should be taken in the selection and sizing of coverings to ensure that the light is fully blocked.

Figure 3: Types of glare and positioning to reduce glare

Figure 3: Types of glare and positioning to reduce glare

Where possible, terminals should be positioned such that the operator's line of sight is parallel to windows and overhead fluorescent lights (see Figure 3). Workstations should be located between rows of overhead lights.

Direct and indirect glare from overhead lights can also be controlled by parabolic filters. These are light-fixture covers that allow light to travel only straight down and not to disperse at an angle, providing sufficient light while minimizing reflection on computer screens. Another option is an indirect lighting system designed such that the light from fixtures does not shine into the work area directly but only after being reflected off ceilings and walls. The lighting system should allow for uniform light levels.

Anti-glare screens should be used only after other methods have proved unsuccessful. Although these reduce indirect glare from the screen, the mesh types also tend to attract dust, and some glass models create more reflections. This may increase visual demands on the operator.

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