Lighting Design For Enhancement Of Visual Performance in Work Place

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A good lighting system must provide suitable lighting for all employees, whatever their task and whatever their age. Older employees require higher levels of illuminance to achieve the same levels of visual efficiency.

 Therefore the level of illumination may need to be increased; this is most easily achieved by the use of local lighting. Care must be taken to ensure that this additional lighting does not become a glare source to other employees working in the surrounding area. Older individuals are more sensitive to glare than the young, due to increased light scattering within the eye and also take longer to adapt from one lighting level to another.

Light can be used for several purpose:

1. To aid and facilitate the performance of a visual task.
2. To create an appropriate visual environment, i.e aesthetic appearance.
3. To ensure safety of people.
4. To provide security for premises.

Lighting during the day can be provided by daylight, electric light or a combination of both. People usually prefer to work in daylight and dislike being in rooms with no windows. However, windows can create uncomfortably hot conditions when there is plenty of sunlight and may also act as sources of glare. The most common approach to interior lighting is therefore to use both daylight and artificial light sources together to produce the required task lighting; the artificial light acts as a supplement to daylight when and where it is insufficient. In this post, I'm going to dwell more on artificial lighting.

Artificial lighting

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There are several methods by which a task
may be illuminated. The three most common in use are referred to as: generalized lighting, localized lighting and local lighting.

General lighting system

These are lighting systems designed to provide an appropriate uniform illuminance over the entire working area. This has the advantage of allowing flexibility of work stations as there is even illumination over the working area. However, energy is wasted because the whole area is illuminated to a level needed for the most critical task. It is therefore more costly than it need be.

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Localized lighting

This system is designed to provide the required illuminance on the working surface together with a lower level of illuminance for other general areas. The difference in illuminance between the task and general areas should be in the ratio of 3:1 or less. Great care must be taken at the design stage of this system to match the lighting to the work stations. If at a later date, the work stations are relocated, there may be a problem with fixed luminaires. This can be overcome if uplighters (stand or desk-mounted) are used as they can easily be moved to a new location.

Localized lighting will generally use less energy but may require more maintenance than generalized systems.

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Local lighting

This has two separate lighting systems: one to provide the ambient background lighting and the other to provide supplementary lighting at the task. Local lighting is a very efficient method of providing high task illuminance which can be flexible, directional lighting for detailed tasks.

It is also a method whereby additional lighting can provided at the task, the luminaire usually being mounted at the work station. Care must be taken when positioning the luminaire at the work station so that it does not create veiling reflectances or shadows or become a glare source for the surrounding workers. Local light should not be placed directly in front of the worker as it will reduce visibility. The best position is to the left of the work station or desk if the worker is right-handed, so that the reflections will mainly go across the worker's line of sight. For left-handed workers the local light should be positioned to the right. The task to background illuminance ratio should not be less than 3:1

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This system has the advantage of providing the necessary level of lighting. But, unfortunately, the luminaires may be inefficient, rather expensive and have higher maintenance costs due to increased wear and tear.