Good lighting design is a significant factor in achieving a comfortable working environment and maximising the productivity of the workforce. Yet achieving comfort is not always that simple.
Probably one of the greatest challenges facing anyone involved in designing building services is achieving an indoor environment that suits everyone. In the case of a comfort parameter like temperature there are clear guidelines. In the case of lighting, there are no such clear definitions and there are no laws dictating the lighting levels for particular areas– other than those relating to emergency lighting.

What we have instead are the CIBSE Lighting Guides, which are seen as defining best practice. In the event of an employee complaining about lighting, and in the absence of any specific laws, a trade union or industrial tribunal will, therefore, refer to the Lighting Guides to press a case.

Particularly relevant to providing a comfortable lit environment is Lighting Guide 3 (LG3), which includes guidance on how to avoid glare on computer screens. Unfortunately, the way that LG3 has been interpreted in many lighting schemes has spawned a host of decidedly uncomfortable lighting arrangements, often because a lot of people have not read the guide properly or have interpreted its advice wrongly.

This problem arises from the use of cut-off luminaires to prevent glare on display screens, with most projects opting for LG3 Category 2 luminaires with a 60 degree cut-off. Used on their own, these have the effect of creating islands of light around workstations, separated by puddles of gloom where the light doesn't reach – hardly an ideal working environment.

"The regulations have often, incorrectly, been used as a bible and once they are in the specification it is difficult to get them out again," explains Oscar Faber lighting specialist, Simon Dicks. "The increasing focus on creating a comfortable environment is partly a reaction against the overuse of Category 2 luminaires," he adds.

Reduced daylight entering many office spaces caused problems. "I think the problems began when we started using mechanical ventilation and air conditioning," says Bob Venning of Arup Lighting. "When we designed for natural ventilation the buildings were not so deep and there were plenty of opening windows on both sides of the building, so there was plenty of daylight. Comfort only became an issue when we starting sealing the buildings, made them deeper plan and concentrated the light."

Much of the current thinking about comfort stems from the need to get away from the cave like effect created by rows of Category 2 luminaires, and getting back to wider light distribution: "A comfortable visual environment goes beyond lighting simply for the task," notes Paul Littlefair of the Building Research Establishment (BRE). "A bright cheerful luminous environment requires light room surfaces, especially walls and other vertical surfaces; in larger spaces the ceiling brightness is also important. These are the forgotten lighting parameters, but they are just as important as working plane illuminance as far as the overall 'feel' of a space is concerned."

Many of the factors that contribute to visual comfort are part and parcel of being human. Despite a few thousand years of confining ourselves in buildings we are still psychologically, and perhaps physiologically, tuned in to the natural patterns of daylight. "All lighting practitioners take their design 'clues' from the natural world, the natural world that has programmed us over hundreds of thousands of years" observes Mike Simpson, president of the Society of Light & Lighting.

The natural condition is one of a constantly changing pattern of light intensity and colour temperature. "We can change the lighting levels and we can change the colour of the light so why not have a changing light pattern that parallels natural daylight to create a more interesting work environment," suggests Hoare Lea's Dominic Meyrick. "We can start to bring in some of the principles of theatrical lighting but in a more subtle way. It has to be practical enough that the end user can buy into it," he adds.

In most cases the budget will determine how adventurous and sophisticated the lighting scheme can become but a lot more can be done with freely available and relatively cheap luminaires. Direct/indirect luminaires combine the downlighting for tasks with some uplighting of the ceiling to give a brighter and more airy feel to the space. Wallwashers or wall-mounted uplighters will add to this feeling of spaciousness by increasing the levels of vertical illuminance.

There is also a case for highlighting certain architectural features or works of art in the space. "Where people are working at a screen, they need to be able to relax their eye muscles by looking into the distance," explains Barry Hannaford of lighting design consultancy DPA. "Where there are no windows to provide views of the outside, you can provide a distant point of interest by lighting certain features at a higher illuminance."

A few years ago it was important that the lighting provided enough horizontal illuminance for paper-based tasks to be performed anywhere in the space. As more work becomes screen based, the convention of 500 lux on the working plane becomes less relevant. However, there will be times when the horizontal illuminance needs to be increased so some control of the lighting, even if it's just a desk lamp for task lighting, is important.

Part of the reason that most of us feel more comfortable at home is that we have control of our own environment. "Part of the office design should counteract the feeling of being out of control," suggests Dominic Meyrick.

Bob Venning agrees: "We should be putting more emphasis on control as an element of visual comfort, using automatic lighting control with manual override within limits. Controls can also be used to increase the visual interest."

Another advantage of providing more control is that individuals have their own preferred lighting levels. In a recent study1 of 12 office buildings, researchers from the University of Liverpool and BRE measured light levels in spaces where people did have control over the lighting. They found that people wanted to work under a wide variety of illuminances, and often well below the standard levels (figure 1).

There is wide agreement amongst lighting designers as to what creates a comfortable lighting scheme. Nevertheless, Category 2 luminaires are not that easy to get rid of: "We had a client that was determined to have Category 2 because they were concerned about being sued by their employees," recalls Simon Dicks. "They had no idea what they were asking for but they were sure it would protect them in court."

This situation has made LG3 unpopular with some: "The lighting guides should be scrapped and we should start again. We need to have guides but we need to completely rethink them," suggests Dominic Meyrick:
A competent lighting designer can achieve a comfortable lit environment while complying with LG3. All it takes is a bit more thought and discussion with the client. The cost of lighting a workstation is equivalent to about half an hour's pay for the average office worker – yet the impact that good lighting can have on a company's bottom line through improved morale and productivity is enormous.

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