Good workplace lighting
The eye is the principal human sense: nearly 80% of all sensory impressions are attributable to visual perception. Special care must therefore be taken over the visual faculties when an ideal working environment is provided. Natural lighting alone cannot meet all the needs for good workplace lighting and must be supplemented by suitable artificial lighting.
As the eye is the organ by which we receive luminous phenomena, we cannot see unless adequate light radiation exists. The properties of light can be defined by various photometric parameters such as luminous flux, luminous intensity, degree of lighting and luminance. Determination of these values is the basis for all lighting which satisfies today’s ergonomic criteria.
Good workplace lighting
The creation of a suitable lighting system must satisfy the following quality criteria: avoid zones of excessive shadow, respect an adequate level of lighting, avoid dazzle and guarantee a uniform distribution of luminosity.
Avoid excessive shadow zones
To ensure good visual perception in space, the human eye needs shadows. Shadow is determined by the precise relationship between horizontal and vertical light. Shadows are indispensable to the plastic perception of a space and the objects within it. The environment in a room with diffuse lighting without shadows is often monotonous and can cause human beings to feel uncomfortable. On the other hand, excessive shadow zones resulting from inadequate direct lighting may cause optical illusions or create a sentiment of insecurity. The ideal distribution of the shadows depends on the effective ratio between diffuse light and directional light.
To obtain balanced shadow zones at the workplace, the following measures must be taken:
- install lighting strips with individual controls and optimise the distance between these lighting strips depending on their luminous intensity;
- place the lighting units in such a way that their longitudinal axis is parallel to the windows. Modulate the natural lighting by installing a suitable system of blinds etc.
Ensure an adequate lighting level
An adequate lighting level guarantees perfect vision and is a fundamental requirement for all mental and physical activity. On the other hand, inadequate lighting reduces contrasts, atrophies perceptions, reduces personal activity and causes the body to go into a rest phase.
The ITM (Labour and Mines Inspectorate) has stipulated minimum requirements as a function of the type of activity which must be respected when workplaces are designed. They are set out in publication ITM-ET 32.10 which deals with standard safety provisions for the protection of workers. Here are some examples:
Type of activity
Lighting in lux
Big offices with average reflection
Big offices with high reflection
To guarantee an adequate lighting level, this must be correctly determined as soon as the office lighting is designed. The fact is that due account must also be taken of variations in the nominal luminous intensity which changes throughout the period of operation of the installed lighting system. In the case of a new installation, the nominal value is 25% higher than the planned value. In this way account is taken of the reduction of the lighting level as a result of the ageing and deterioration of lamps and light fittings on the premises. Maintenance work on the lighting equipment must be put in hand when the average lighting level has fallen to 80% of the nominal value. The lighting level must never fall below 60% of the requisite nominal value.
The need for light increases with age. The retina becomes cloudy and the visual faculty diminishes. Higher levels of lighting must therefore be provided for older workers.
Unsuitable artificial lighting and the use of natural light can cause dazzle, even if this is not consciously perceived. This dazzle is generated by excessive levels of luminance or by excessive luminance ratios caused by the presence of windows lit by natural light with no possibility of closing blinds or, for example, the presence of reflective surfaces.
An agreeable distribution of light must be assured by attaching considerable importance to harmonious contrasts. A simple rule advocates a luminance ratio of 1:3 between the field of work and the immediate environment and of 1:10 between the workplace and the peripheral environment.
Dazzle obstructs the visual faculty, even if it is not consciously perceived. A distinction is made between direct dazzle and dazzle caused by reflection.
- Direct dazzle can be caused by inadequate light sources situated in the operator’s field of vision or by a poor choice of workplace location in relation to natural and artificial light sources (example: workplace facing a window).
- Dazzle by reflection reduces the contrast needed for good visual recognition. These disturbing reflections occur, in particular, at the screens or other display units.
Recommendations to be followed to avoid dazzle
- keep the workplaces away from windows;
- arrange the workplaces perpendicular to windows; the operator’s direction of gaze must be parallel to the windows;
- place the workplaces directly underneath the lights; if these lights are rectangular, their longitudinal axis must be parallel to the windows and to the direction of the operator’s gaze;
- use lights with an opening angle α ≥ 30° as stipulated in DIN 5035 standard, Part 7;
- install a system of blinds enabling the natural lighting of the premises to be modulated and permitting a view of the world outside;
- make the maximum possible use of mat and semi-mat surface treatment for the layout of workspaces;
- choose modern screens with anti-reflection treatment and positive display software (dark characters on a white background).
The different lighting systems
Light fittings can be divided into various categories, depending on the method of distribution of the luminous flux, i.e. the way in which the luminous flux emitted by the light fitting reaches the work surface. This plane is generally horizontal and located at a height of 0.85 cm. A distinction is drawn between three main categories: direct lighting, indirect lighting and direct/indirect lighting.
- Direct lighting is naturally the most appropriate method of lighting to achieve maximum photometric efficacy. The light is not deviated but oriented directly on to the surface to be lit, i.e. the work surface. In general lights fitted with a grid are used. The grid ensures a luminous flow free from reflections. The problem which arises in this case is the uneven distribution of brightness throughout the room. Ceiling lighting is less pronounced and the peripheral surfaces receive less light. The walls show clear conical spots. This phenomenon can result in eye fatigue and an impression of discomfort which is called the “cave effect”.
- In the case of indirect lighting, the light is first fully reflected for instance by the ceiling before reaching the surface to be illuminated. It therefore loses some of its efficacy and the photometric yield is reduced. The advantage of this type of lighting is that the other surfaces of the room, such as the walls, also receive light and appear pleasantly bright.
- The direct/indirect system combines the two systems described above. It groups together the advantages and drawbacks and often represents a good compromise between efficacy and visual comfort.
Criteria for good lighting
Discussion of good workplace lighting is such a vast subject area that we have set out below a summary of the most important points to be respected when a lighting system is designed and installed.
- Avoid at all cost dazzle caused by light fittings.
- Light must be installed away from the line of sight, i.e. the workplace must be installed between the vertical positions of the light fittings. The line of sight between the screen and operator must be parallel to the windows.
- Only use light fittings with an opening angle which prevents all risk of dazzle.
- Lighting strips must be arranged in parallel to the windows.
- Take maximum advantage of natural lighting.
- Avoid big differences of brightness in the operator’s field of vision. The lighting of the premises must be uniform.
Environment and furniture
To counteract all risk of dazzle and reflection, the surfaces of the furniture and office equipment must have a mat finish. The choice of colours for the walls, ceilings, floors, furniture and office appliances must correspond to the level of reflection recommended for workplaces.
Design and maintenance
- A lighting expert must be entrusted with the design of the lighting system.
- An expert may be asked to approve the installation before it is commissioned and the installation must be verified at three-yearly intervals.
- A maintenance plan must be drawn up which determines the time at which the light fittings are to be cleaned and bulbs changed for example.
Which particular points require attention?
- Make sure that the nominal value of the lighting intensity is 500 lux for workplaces at which visual display screens are used.
- Avoid pronounced shadows.
- Only use extra lighting, such as office lamps, in combination with a general lighting system.