Lighting at work is very important to the health and safety of everyone using the workplace. The quicker and easier it is to see a hazard, the more easily it is avoided.
The types of hazard present at work, therefore, determine the lighting requirements for safe operation.
Inadequate lighting can be a component cause of many kinds of accidents at work. The avoidance of accidents requires the recognition of danger. A very large proportion of the information that warns of impending danger is received through the sense of sight, but recognition is only complete when the brain interprets the information correctly.
An accident may be caused by:
• A failure to see • A failure to understand what is seen
The importance of careful lighting design is clear and, in health and safety, it is suggested that optimum lighting should create conditions that are comfortable to the eye and in which all relevant information can be received through the sense of sight.
Those in charge of workplaces need to identify priorities and set targets for improvement. For example, they will need to assess whether the lighting design is suitable and safe for the type of work being done.
We also need to consider any future changes in the work conditions, as this may require different lighting designs.
The costs and benefits of different lighting design will then need to be considered together with the suitability of lighting for the workplace.
The principle for organising for health and safety involves the provision of staff with the necessary training and appropriate equipment to do their job safely.
This includes those responsible for lighting maintenance. We also need to ensure that staff are aware of their responsibility towards their own health and safety and that of other people. For example, it is important that staff notify line management if lighting is faulty or damaged.
Furthermore, we need to include our staff in the planning and promotion of health and safety, as it is often staff that are the first to notice any hazards. If we involve staff it will ensure that they are committed to improving health and safety at work.
Controlling health and safety risks includes the setting of standards and maintaining them. Standards set need to be realistic and measurable, and may include lighting maintenance so that it does not interfere with work activities. This would then ensure that lighting is checked on a regular basis and that correct lighting levels are maintained.
The monitoring and reviewing of lighting conditions is important in ensuring proper health and safety performance. Monitoring involves checking how far set standards have been met. Reviewing involves the checking of standards, planning, control and organisation and changing them when necessary to improve health and safety. For example, installing new lighting designs may create different health and safety risks; therefore, standards need to be changed or altered.
There are several lighting hazards in the workplace that can affect the health and safety of people. Typical risks from lighting originate from:
• Lighting effects • Incorrect lighting design • Improper lighting installation, maintenance, replacement and disposal • Improper selection of emergency lighting
Suitable workplace lighting
The mechanism of sight and the basic properties of lighting are interrelated when discussing the suitability of workplace lighting. The following factors must all be considered when designing or evaluating the suitability of workplace lighting:
• Contrasts and contract rendering • Disability glare • Visual comfort • Modelling of 3D tasks • Colour rendering • Flicker and stroboscopic effects • Lighting for movement between work spaces • Natural light, sunlight and solar control
Each of these will now be briefly discussed in turn.
Contrasts and contrast rendering
Visual performance tests confirm that the acuity with which tasks are seen is improved when lighting levels are increased. However, they also show that a stage is reached at which any further increase in illuminance produces a disappointingly small improvement in visual performance. In the case of low contrast tasks more substantial improvements are often achievable by other means.
The background against which small detail is examined should be as plain as possible. Anyone who has searched for something small that has been dropped onto a carpeted floor will know that it is more easily found on plain carpet than on one which is densely patterned. Too many contrasts in the field of view are confusing to the eye.
Shiny surfaces, such as those of polished metals, plastics, glass and gloss paints are among the most difficult to light satisfactorily. Where possible they should be avoided in favour of matt surfaces because they may reflect distracting images or give rise to veiling glare. It is important in the work environment to try and direct troublesome reflections away from the eyes.
The effectiveness of a lighting installation in revealing the contrast in a task is called contrast rendering and this may be improved by:
• Altering the position of light sources or their intensity distribution(s) to change the direction from which the task receives light • Altering the position of the task and/or the direction from which it is viewed
The presence of a very bright source of light in an otherwise normally lit field of view causes severe adaptation problems for the eye. In extreme cases the situation is made worse by the scattering of light in the lens of the eye. Any consequent reduction in visual performance is said to be the effect of disability glare.
Disability glare from a particular source may be reduced by:
• Moving the source or changing the line of sight • Reducing the intensity of the source – either the source itself or by utilising blinds, louvres, diffusers and so on
Visual comfort at the work station
It is a common experience that fatigue and the consequent loss of performance occurs more rapidly in uncomfortable conditions. Concentration is more easily maintained and careful work more probable when it is carried out in comfort.
The eye is naturally attracted to the brightest part of the field of view. Bright objects displaced from the line of sight are a distraction and may be a source of glare. Good task lighting will therefore make the task the natural centre of attention by making it the brightest part of the visual field.
When the pattern of luminance at the workstation deviates significantly from the ideal described above, acute discomfort may be experienced as a result of discomfort glare. Like disability glare, discomfort glare is caused by excessive luminance contrasts to which the eye cannot satisfactorily adapt.
Modelling the task
Overhead general lighting installations, designed to provide uniform glare free lighting, sometimes result in poor modelling. Local lighting may be used to introduce an additional component and so improve the modelling of tasks that require accurate perception of shape and texture. For example, textural effects (such as imperfections in surface coatings) are best revealed by directional light arriving at a glancing angle on the surface under inspection.
Although certain types of tasks need especially strong modelling, most will benefit from an arrangement that provides some light from all directions, such as a diffuse component. Light which is initially directed away from the task may be reflected from neighbouring (matt) surfaces and so become diffused. As this is indirect, the diffuse component of the light is increased and the result is usually more gentle modelling.
Light that has good colour rendering properties reveals the colour of the surface it illuminates in such a way as to permit reliable colour judgements. Colour coding is common in many workplaces, especially for hazard warning and control.
In some industries accurate colour judgements must be possible at the workstation. Even if special demands are not made by the work itself, the quality of the working environment will suffer if the light so distorts colours as to make them appear unnatural to the eye.
Flicker sensitivity and stroboscopic effects
All sources of light powered by alternating current supplies are subject to fluctuations in their output. These are seldom apparent from filament lamps, but are more often seen as a high frequency flicker in the output from discharge sources. This effect may grow worse as fluorescent tubes age.
In some particularly sensitive individuals, the flicker itself may induce visual discomfort or headaches, but greater risks to all may arise from certain optical illusions that can occur when the light falls upon moving machinery. Any rapidly repeated movements may appear to be slowed, halted or reversed in direction, with the result that hazards presented by such machinery are not always recognised.
These stroboscopic effects may be reduced when the general illuminance provided by fluorescent or high pressure discharge sources is swamped by local filament lighting. More generally effective measures include the division of the lamps between the phases of a three phase electrical supply (with adjacent luminaries on alternate phases) or the provision of a high-frequency supply.
Lighting for movement between workspaces
The minimum requirement for circulation areas between workstations is that they should receive sufficient light, appropriately distributed, to allow movement to take place safely and conveniently. This is essential under emergency lighting conditions but is important at other times, too.
Where especially high illuminances are provided locally at the workstations, there is a danger that personnel who are moving between them will not be able to adapt quickly enough to the changing conditions of brightness. This continuous need to adapt will also hasten the onset of fatigue.
The eye is particularly slow to adapt when the general luminance is suddenly reduced. A light adapted eye that is plunged into darkness will take more than half an hour to become fully adapted to the dark. Even when the change is less severe, the process of adaptation may last for several minutes.
If a staircase is negotiated during this period, the hazard presented will be significantly increased. Such problems are avoided when adequate lighting levels are provided along circulation routes to those of the areas they serve.
Natural light, sunlight and solar control
In most circumstances, the controlled entry of natural light will improve the quality of the workplace. To assess its potential and to select appropriate controls we must first distinguish clearly between its two components, daylight and sunlight.
Where it can be allowed and adequately controlled, sunlight is an amenity that is welcomed by most people. However, from the brief comparisons made previously, it is clear that the direct light of the sun does not provide suitable task lighting.
Apart from the fact that the levels as high as the suns 100,000 lux are never necessary, its strong directional light casts heavy shadows and produces harsh contrasts to which the eye cannot satisfactorily adapt.
In most circumstances it is prudent, and in some cases necessary, to provide for the exclusion of sunlight from workstations and their surroundings because it can be a cause of annoyance, discomfort or disability.
Daylight is both suitable for task lighting and valuable as an amenity. It can contribute usefully to task lighting but will not normally be sufficient on its own. Even interiors receiving generous amounts of daylight at the brightest part of the day will need artificial lighting to:
• Supplement daylight when it is not sufficient • Provide all necessary light after daylight hours
In conclusion, to ensure appropriate productivity and to reduce harm and discomfort, the provision of lighting and the maintenance and conducting of lighting surveys is an essential tool. From the design to lighting for a workspace to the utilisation of natural daylight, if we do not see the hazards in our workspaces then it becomes inevitable that the risk they pose will be realised. We must, therefore, ensure that a light is shone on these hazards and they are appropriately controlled.
Published: 15th Dec 2015 in Health and Safety Middle East