Light work

Citation

(2003), "Light work", Work Study, Vol. 52 No. 4. https://doi.org/10.1108/ws.2003.07952daf.003

Light work

In recent years the importance of lighting in the workplace – and its effects on both comfort and productivity levels – has been recognised. The developing understanding of these inter-relating factors has led to changes in the Building Regulations and the UK Society of Light and Lighting's Lighting Guide 3. A basic understanding of these changes is useful when appointing a lighting consultant or installer.

Approved Document L2 of the Building Regulations deals with energy efficiency in buildings other than dwellings and it has been focusing more and more on the efficiency of lighting in recent years. The latest amendments came into force in April 2002 and apply to buildings and parts of buildings where more than 100sq.m. of floor area is to be served by artificial lighting. However, they do not apply to emergency lighting, specialist lighting (such as signs or medical lighting), external lighting, portable lighting or period lighting such as chandeliers.

With lighting, professionals use the term "efficacy" rather than "efficiency" because of the way different lamps convert electrical energy to light. An obvious and familiar example is the ability of fluorescent lamps to produce more light than a traditional incandescent light bulb from the same amount of electrical energy.

One significant change relates to the way that the average efficacy of a lighting installation is measured. There has been a shift in emphasis from circuit efficacy to installation efficacy. The measurement used to be lumens per circuit-Watt (lm/W) but has now changed to luminaire-lumens per circuit-Watt.

This means that the regulations now relate to more than just the efficiency of the lamp or light source, they relate to the whole light fitting – encompassing the lamp, the control gear (ballast and choke), the luminaire and the use of control systems. This is particularly important because it means that the efficiency of every aspect of the system needs to be considered.

As Approved Document L2 states: "A way of meeting the requirements would be to provide lighting with an initial efficacy averaged over the whole building of not less than 40 luminaire-lumens/circuit-Watt. This allows considerable design flexibility to vary the light output ratio of the luminaire, the luminous efficacy of the lamp or the efficiency of the control gear."

The result is that the designer can average out the overall efficacy by using highly efficient lamps in one area and less efficient lamps in another. There is also the option of ignoring 500W of the installed lighting in the calculations, providing some scope for less efficient feature lighting.

The Regulations now also make more reference to daylight and the benefits of using lighting controls to adjust artificial lighting in relation to the amount of daylight entering the space.

An effective lighting scheme that enhances the comfort of the workforce and encourages greater productivity has to take account of a number of other factors, beyond just the energy efficiency. In November 2001 the Society of Light and Lighting (SLL) took measures to clarify what constitutes best practice. To that end, Lighting Guide 3 (LG3), The Visual Environment for Visual Screen Use, has been amended, with the withdrawal of the luminaire category rating system – the system that led to the almost ubiquitous "Cat 2" luminaire. In fact, one problem with LG3 was that it offered a quick and easy route to compliance through the use of Category 2 luminaires, widely and cheaply available. This tended to result in "Cat 2 installations" rather than effective lighting designs. The SLL now expects every lighting installation to include consideration of the quality of the working environment.

Category 2 luminaires were set to provide a cut-off of light at an angle of 65° so that the potential for glare on screens was minimised – but controlling the light distribution is only part of the equation. "Considering only the luminaire's light distribution does not guarantee a successful lighting installation", says the revised LG3.

Just how compliance is achieved will vary from one installation to another – but most important is that installations should comply. If, for example, an employer is taken to a tribunal for a case which involves a claim of inadequate lighting, a significant defence is that the lighting was designed in accordance with professional guidance and, therefore, every reasonable precaution has been taken. The alternative – of proving that the lighting is acceptable – is very difficult.