Last reviewed 14 August 2013

Robert Stuthridge describes how lighting may be used to maximise health, safety, inclusion and productivity.

We humans perceive our environment predominantly through our sense of vision and without light there can be no vision. Yet lighting is not merely about making tasks visible; it affects people physiologically, psychologically and emotionally; it can be used to optimise health and productivity, and to aid in the accommodation of those with visual disorders. For these reasons, it is useful to be able to identify lighting problems commonly encountered in the workplace, and to know how to eliminate them.

Lighting problems

Lighting problems can be divided into three main categories — quantity (too much or too little illumination), quality (colour, flicker) and direction (shadows, glare). In addition, the visual task may compound lighting deficiencies if it offers poor contrast or legibility, or is inconveniently located.

Gloomy environments are those providing light insufficient for someone to perform visual tasks without adopting awkward postures (flexing the neck or trunk to reduce visual distance to the task), or which render potential hazards hard to detect by sight alone. Light insufficiency is, in part, subjectively determined, varying between workers performing the same task. Increasing illuminance may be the most obvious intervention, but improving the contrast between tasks and their backgrounds, and increasing the reflectance of walls, floors, and ceilings may also improve task visibility.

Glare

Glare occurs when an excessively bright light intrudes into the field of view. This can happen directly via unshielded lamps, or sunshine entering through bare windows; it can also occur indirectly when light bounces off highly reflective surfaces. Glare can render parts of the environment invisible, disabling the worker by preventing task performance, or making it unsafe. An example of "disability glare" is when approaching undipped headlamps force a "blinded" driver to slow down or stop. The term "disability glare" is also used when bright light sources cause problems for workers who have visual impairments, such as cataracts, macular degeneration, glaucoma, or diabetic retinopathy.

Glare can be managed in several ways. Unshielded lamps and bare windows may be fitted with shades or diffusers. If possible, redirect light onto walls or ceilings, providing worker-adjustable task lighting as necessary. Eliminate reflected glare by repositioning the light source and/or the worker's task, or by refinishing reflective surfaces. Glare can be a relative problem; a bright light source will be more problematic in a gloomy room than in a well-lit one, so equalising illuminance in the room can help.

Specular glare occurs when a bright, reflected image obscures the surface onto which it falls. Reflections on windows can render them opaque. This can be problematic if transparency is critical to safety, such as when using glazed swing doors, as a user may not see someone approaching from the opposite side. It can also obscure displayed items, such as in shop windows. Shading, transitional lighting, and the use of non-reflective glass are ways to reduce specular glare on windows. Specular glare from reflective surfaces can be resolved by repositioning the surface or redirecting the incident light source.

Colours

Accurate colour rendition is highly dependent upon lighting. Objects absorb or reflect spectral bands from light falling on them, affecting our perception of their colour. Lamps may be rated for colour accuracy. The Colour Rendition Index (CRI) rates at 100 a light source (eg daylight) that accurately renders colour of objects. CRI is not without its critics, but remains useful for comparing light sources. A CRI of less than 80 is not recommended where colour accuracy is critical. Low pressure sodium and “daylight” fluorescent lamps typically have CRIs of -44 and 76 respectively. Cool white triphosphor fluorescent, incandescent, halogen, and some LED lamps have CRIs approaching 100.

In dark environments, our ability to discriminate colour is impaired. At low light levels, receptors in our eyes known as "rods" become dominant over "cones." Cones are sensitive to colour, detail and contrast in the central field of view, and operate in well-lit environments. Rods provide peripheral vision (where colour perception is relatively poor) and movement detection. Ensuring sufficient illumination to stimulate the cones is essential for tasks requiring colour discrimination.

"Temperature" of lighting in Kelvin (K) provides an indication of the whiteness of light emitted, 5000K and higher being "cool" (blue-white), and 2700–3000K being "warm" (red to reddish-white). People with cataracts typically prefer slightly warmer lighting. Workers with visual disorders that are highly sensitive to light temperature may be assisted by using prescription coloured optical lenses or by providing adjustable lighting temperature and brightness controls.

Blue light hazard

Blue light hazard (BLH) is the potential for injury when the retina is exposed to high energy short wavelength light (400–500nm on the electromagnetic spectrum). BLH may arise from a variety of lighting types, including LEDs. CELMA advises against exposing children to high energy blue spectrum lighting, because children do not filter blue light as efficiently as adults. It may advance macular degeneration (AMD), but there is some debate over blue light as a cause of AMD. It seems prudent to minimise exposure to high energy short-wave lighting, or to wear blue-light blocking lenses when unavoidably working in such environments.

Flicker

Flicker is the rapid fluctuation of light intensity, often associated with fluorescent lamps. It increases risk for eyestrain and headaches, especially for migraine sufferers. People generally detect flicker rates up to 50Hz (Hz are cycles/second), with 10–25Hz being most noticeable, although the sensory system responds to higher rates. Flicker can be eliminated by maintaining lighting components in good order, replacing lamps before they deteriorate, using energy efficient electronic ballasts (20kHz–60KHz), and by mixing lighting types, rather than relying on fluorescent lamps only.

Inclusive design

Age

Because eyesight changes with age, typically deteriorating in terms of visual acuity (sharpness), accommodation (adjustment to visual target distance), and contrast resolution, lighting that meets the needs of a younger worker may not be appropriate for an older worker. Older workers may need significantly higher levels of illumination to perform tasks comfortably and efficiently; optimise the location, contrast, clarity and size of visual tasks.

Visual disorders

People with visual disorders may be particularly sensitive to lighting. Personal preferences for lighting may vary considerably, but generally, interventions or accommodations involve eliminating glare, maximising legibility and contrast of visual targets, and equalising lighting to eliminate strong shadows or sharp differences between illuminance levels in adjacent areas.

Psychological disorders

Lighting affects the endocrine system. Working in dimly-lit environments will trigger the release of the "sleep hormone" melatonin, reducing alertness, and increasing error or accident risks. Depression and seasonal affective disorder (SAD) may both be affected by light, and can be problematic during the short winter days of Northern latitudes. Light therapy is as effective as anti-depression drug therapy for these forms of depression. This involves sitting close to a lamp emitting at least 10,000 lux for about 30 minutes daily. SAD sufferers undertake the therapy in the early morning to simulate sunrise. Potential side effects include headaches and eyestrain, and certain drugs may increase sensitivity to light, so that light therapy should only be undertaken under medical supervision.

Individual preferences

There is no such thing as "one light fits all"; there will be individual preferences that can only be accommodated — where safe, practicable, and affordable — by enabling each person to adjust the lighting for their tasks. This may mean providing task lamps with adjustable output settings to supplement under-cabinet lighting or ceiling luminaires. Such flexibility is useful if workers "hot desk".

Posture

People adapt posturally to lighting in various ways. In dim lighting, gait may become slowed with shorter steps, particularly for older adults. Workers lean towards poorly-lit tasks to shorten the visual distance, adopting postures associated with back and neck pain. Glare avoidance may involve adopting postures to remove the source of glare or reflection from the worker's field of view. These postural effects are resolved by providing optimal task lighting to suit each user, and by eliminating glare using shielding, shading, or source repositioning.

Productivity

Lighting can increase productivity, especially when worker-adjustable illumination is provided. One study reported a 4.5% increase in productivity by enabling individual control over lighting (The Influence of Controllable Task-lighting on Productivity: A Field Study in a Factory, Juslén H, Wouters M and Tenner A, Applied Ergonomics, 2007). Reasons cited for the increase included optimal task visibility and biological (circadian rhythm) factors.

Safety

In poor lighting conditions, risk increases for vehicular collisions and pedestrian trips and falls. Hazards may be difficult to see in dim lighting, or where glare is present. Steep differences in light levels between work areas increase risk. Moving from a bright to a dark environment results in temporary blindness lasting up to 30 minutes as the visual system adapts.

Transitional lighting should be used to equalise illuminance between work zones, ensuring that potential hazards are minimised using strong contrast, spot lighting, and physical barriers. Workers operating close to vehicle access routes in transitional environments should be protected by barriers, and/or wear high-visibility clothing. All workers should be trained to increase awareness of the heightened injury risk in such areas, and suitable warning signs should be displayed.

Conclusion

An ideal workplace lighting scheme will allow individual control over lighting illumination, hue, and direction, maximise contrast between objects in the visual environment and their background, minimise flicker, and eliminate glare and reflection. In reality, such an ideal is difficult to achieve. However, a simple lighting survey including input from workers who use the environment may reveal problems that are not difficult to eliminate. Gaining universal agreement on optimum lighting is unlikely, but the benefits to health, safety, and productivity make this a goal worth pursuing.

Further information

A wealth of technical information is available. Of particular relevance to the occupational setting are the following.

  • ISO 8995-1:2002 Lighting of Work Places. Part 1: Indoor

  • ISO 8995-3:2006 Lighting of Work Places. Part 3: Lighting Requirements for Safety and Security of Outdoor Work Places

  • ISO 30061:2007 Emergency Lighting

  • Basic Vision: An Introduction to Visual Perception, Snowden R, Thompson P and Troscianko T, Oxford University Press, Oxford, 2012 (2nd ed)

  • Ergonomics, Work and Health, Pheasant S, Macmillan Press, London, 1991

  • Human Factors in Lighting, Boyce P R, Taylor & Francis, 2003 (2nd ed)

  • The Royal National Institute of Blind People website