Guiding light

Towards the tail end of the year, the lighting industry saw some significant changes in the requirements for lighting design to comply with the Building Regulations and CIBSE Lighting Guide 3. Anyone involved in lighting design needs to be aware of these changes if their designs are to comply with both legislation and best practice.

Approved Document L of the Building Regulations, dealing with energy efficiency, has been focusing more and more on the efficiency of lighting in recent years. The latest amendment, Building (Amendment) Regulations 2001 which comes into force in April 2002, is no exception.

One of the biggest changes is 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," notes Bob Venning of Arup Lighting. "The measurement used to be lumens per circuit-watt (lm/W) but this has now changed to luminaire-lumens per circuit-watt. Also, there is now factorisation for the use of control systems," he adds.

This change takes account of more than simply the lamp efficacy, as was previously the case, and now takes account of all the components that make up the lighting system, such as lamp and control gear efficacy, luminaire efficiency and the use of control systems. This is clearly shown in the equation graphic to the left, used to calculate luminaire-lumens/circuit-watt.

In applying these guidelines, Approved document L places emphasis on office, industrial and storage buildings, saying: "Electric lighting systems serving these buildings should be provided with reasonably efficient lamp/luminaire combinations. 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."

So, just as before, it was possible to average out the overall efficacy by using highly efficient lamps in one area and less efficient lamps in another, so the same can be done under the new guidance. There is also the option of ignoring 500 W of the installed lighting in the calculations, providing some scope for less efficient feature lighting.

As noted earlier, lighting controls now play a more important role in the calculation of installation efficiency, with use of the factor C_L in the equation and guidance as to how these factors are calculated (see table 1). At the same time, the Regulations are making 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.

In this context, a daylit space is defined as "any space within 6 m of a window wall, provided that the glazing area is at least 20% of the internal area of the window wall. Alternatively it can be roof-lit, with a glazing area at least 10% of the floor area."

This assumes that the normal light transmittance of the glazing is at least 70%, and allows for the glazing area to be increased if glazing of lower than 70% transmittance is used. However, any increase in the glazing area needs to take account of insulation values and solar gain, and maximum areas for glazing are also provided in the Approved Document (see table 2).

While increased reference to daylighting has been welcomed by lighting designers, most of whom have been working effectively with daylight for many years, there are suggestions that the current regulations have not gone far enough. "It's good that daylighting is included now but the current reference does not help in design for those people who are unfamiliar with it," notes Venning. "For example, using a 6 m depth is not very meaningful because there will be so much variation between areas close to a window and areas 6 m away. Also, there is no account taken of the way light will vary between a city site and an open site, so I think they should be moving towards recommending a daylight factor," he continues.

For types of building other than office, industrial and storage premises, the Regulations recognise that: "…. it may be appropriate to provide luminaires for which photometric data is not available and/or are lower powered and use less efficient lamps. For such spaces, the requirements would be met if the installed lighting capacity has an initial (100 hour) lamp plus ballast efficacy of not less than 50 lamp lumens per circuit-watt."

To achieve this, the document recommends providing at least 95% of the installed lighting capacity using lamps with acceptable circuit efficacies and provides a list of suitable light sources and power consumption of control gear (see tables 3 and 4).

For retail applications and spaces used for public entertainment, there is also guidance on display lighting, with recognition that the requirements of this type of lighting may make it necessary to accept lower energy performance. At the same time, the Regulations are keen to encourage some consideration of energy performance and call for the average installed capacity of display lighting to have an initial (100 hour) efficacy of not less than 15 lamp-lumens per circuit-watt. In calculating this efficacy, the power consumed by any transformers or ballasts should be taken into account. Again, a list of suitable lamp types for display lighting is provided (see table 5).

There are a number of other considerations to take into account when designing lighting. As Bob Venning notes: "The Building Regulations are getting more refined and adding more things for people to think about. The requirements are achievable with very little effort but the problems occur when you have people who don't really know what it means so they just go for the minimum. It's very important to remember that the Building Regulations set the minimum values and these need to be achieved by using best practice in lighting design."

Achieving best practice
Last November the Society of Light and Lighting (SLL) took measures to clarify just what constitutes best practice. To that end, Lighting Guide 3 (LG3: The visual environment for display screen use) has been amended, with the withdrawal of the luminaire category rating system – so all those designers who have relied on providing the standard Category 2 installation are going to have give more thought to their designs.

"Environmental issues in the office space are becoming paramount," notes John Craven of Whitecroft Lighting. "If you look at LG3 in 1989 it referred to lighting for display screens, there was no mention of people. In 1996 the terminology changed to the visual environment and problems of images on screens. The new LG3 puts the environment ahead of everything," he continues.

The problem with LG3 has been that it offered a quick and easy route to compliance through the use of Category 2 luminaires, these luminaires have been ten a penny and developers and letting agents have found it easier and cheaper to say "I want a Cat 2 installation" than "give me a good lighting design". In removing the categories, SLL is seeking to ensure that every lighting installation includes some consideration for the quality of the working environment.

"Category 2 was never the only solution but a lot of people have become locked into the Cat 2 syndrome and we have been producing some very poor environments for people to work in," explains Mike Simpson, president of SLL and a director of Concord:marlin. "People have to start looking at lighting design in a different way and, generally, there has been a positive reaction among lighting people to these changes. Our challenge is to explain the reasons for these changes to people outside the lighting industry and wean the developers and letting agents off Cat 2 specifications," he adds.

The major change to LG3 comes in section 8.3.2, which notes that in most cases the luminance limit will be applied at a standard 65° limit angle but also warns: "Considering only the luminaire's light distribution, however, does not guarantee a successful lighting installation. The designer needs to consider all aspects of the guidance in order to design an installation that complies with Lighting Guide 3. The key to success is the avoidance of any very high luminance patches in a space and any abrupt change in luminance across a surface or between adjacent surfaces. It is therefore necessary for the designer to have some influence over the control of daylighting and the specification of the reflectance of ceiling, wall and other surfaces."

In practical terms, this means that designers who have tended to specify just recessed downlighters may have to put their thinking caps on. "If you are just going to have a recessed fitting with a low brightness diffuser, you are not going to meet the requirements unless you're working inside a white cube," warns Simpson. "People should be moving to a multi-product solution and they are probably not going to comply unless they are using at least two luminaire types," he adds.

Just how compliance is achieved will vary from one installation to another, and it's worth noting there are recessed fittings on the market that are able to provide a full wash of light across all four walls from top to bottom. That aside, why should people bother to comply at all? After all, LG3 is guidance, not legislation.

"There are a number of reasons why people should comply," explains Simpson. "If an employer is taken to a tribunal for providing bad lighting, the best defence is that the lighting has been designed in accordance with professional guidance and, therefore, every reasonable precaution has been taken. If that is not the case, the employer then has to prove that the lighting is acceptable, which may be difficult.

"Of course, you could say that we have been lighting with Category 2 for 10 years and there haven't been any cases yet, but the quality of the working environment is also important for employers. Staff may not know the lighting is bad but they will know it's not a very nice place to work and that will make it harder to attract and keep the right staff. As the birth rate falls and there are fewer people entering the job market, this is going to become an increasingly important consideration," he continues.

It will clearly take some time for the message to get through and for people to be dragged, kicking and screaming, away from the comfort of Category 2, but the people who can push that forward are those who are involved in lighting design now.