The latest edition of the SLL Code for Lighting is nothing if not revolutionary. Jill Entwistle takes a look at the latest radical changes to the industry’s design bible

The SLL Code for Lighting has a reputation as the fount of all lighting wisdom. First published in 1936, it gathers all the latest legislation into one source. But its role goes beyond that of a glori ed lighting law – and lore – digest. It is also a commentary on the recommendations, nudging the non-lighting specialist in the right direction, charting the tricky course between guidance and overprescription.

‘It is not just a schedule of lighting levels,’ says Mike Simpson, former president of the SLL and Cibse, and technical and design director of Philips Lighting.

‘More than three-quarters of the current pages are dedicated to good lighting advice that comes from experienced practitioners and will help the inexperienced designer produce a workable design.

There is advice on creating visual effects, assessing task performance, minimising glare, revealing texture and form and ensuring good maintenance over life.

‘In short,’ he adds, ‘if you follow the code you won’t produce a bad design.’

Latest and greatest

The latest edition, launched at the beginning of this year, features some step changes in approach to lighting. Essentially they re ect the latest European workplace lighting standard, EN 12664, which came into force last year.

Peter Raynham, current SLL president and coauthor of the latest code with Peter Boyce and John Fitzpatrick, says these changes are radical. ‘This time it’s a real rethink,’ he says. ‘Basically we took what we had, tore it up and started again.’

He cites in particular the new requirement for cylindrical illuminance, which he says will have most impact in schools and of ces, where the visibility of people’s faces is important to ensure good communications. ‘Classically we would talk purely about lighting visual tasks and now we’ve realised that we have to look at people in offices.’

Not brave enough?

But there is a lobby that believes the changes do not go far enough. These people argue for nothing less than a complete rethink of the way lighting is designed and measured.

Tim Downey, an independent lighting designer andsenior partner of studioFractal, says: ‘Tabulatinga series of tasks and assigning recommended illumination levels for those tasks is an incomplete concept – especially when one can see that the recommended illumination levels for those tasks have been steadily increasing over the past 70-80 years.

‘We are now trying to  nd ways of using less light – or more accurately, less energy,’ he continues.

‘This should mean the same thing, but the rapid advancements in light output from LEDs will soon mean that we can still install far too much light but with a decreased energy load.

‘Our clients don’t want to know if we are designing according to the Code of Lighting; they want to know if we are complying with their target Breeam rating.’

The modification of codes in general is missing the point, says Downey.

‘These editings are concerning themselves more with the edges of things than tackling the elephant in the room. While regular updates to the Code for Lighting are welcome, I believe a more radical approach is required – one that breaks away from the old model of measuring light falling on to surfaces to one based on light emanating from surfaces and reaching the eye.’

Seismic upheavals

Such seismic upheavals in thinking generally take time to gain acceptance. In the meantime, Raynhamwould argue that, at least to prevent bad lighting, the code remains an important guide for the non-specialist.

‘For all the changes in the new edition, the principal nature of the publication has not changed,’ he says. ‘It is still a de nitive reference document that provides a distillation of a huge number of standards, guides and regulations. For that reason alone it will remain an important publication for all people who work with lighting.’

On the brink

Downey is less sanguine. ‘We are on the brink of a massive change in how we illuminate our environments. Ceiling-mounted light  ttings will give way to translucent surfaces – ceilings, walls, floor, furniture – which means there will be more light coming from these surfaces than is falling on them.

‘We must change our way of measuring light to fallinto line with how we see our environments – or we will have an increasingly irrelevant, unused Code for Lighting.’

All change

The key changes in the SLL Code for Lighting are based on the new edition of BS EN 12464-1 Light and Lighting, Lighting of Workplaces – Part 1: Indoor Workplaces. However, the code makes clear that the values given are a minimum.

‘While we might give a value – for example, you need 50 lux on the wall and 30 lux on the ceiling,’ says Raynham, ‘we’re saying that would be a reasonable number but really you should be doing better.’

  • The focus is now on lighting for the task, a recognition that a high level of uniform illumination is only essential in key task-based areas, and can be both pointless and wasteful of energy in other spaces such as corridors. The minimum horizontal illumination in a space can vary between 40 per cent and 70 per cent uniformity, saving energy in background areas as light levels are reduced. A scheme can be installed to light the entire space as a task area but intelligent luminaire and controls will ensure that only appropriate fi ttings are switched on.
  • A key introduction is the idea of mean cylindrical illuminance (measuring vertical illumination through 360 degrees). This encourages designers and specifiers to create schemes that deliver 50 lux on the vertical plane (75 lux for offices and education facilities) at heights between 1.2m (sitting) and 1.6m (standing) above floor level, within activity areas.
  • Where room surface illuminance is concerned, the requirement is 30 lux on the ceiling and 50 lux on the walls. The aim of these minimum illumination levels is to discourage the use of narrow beam downlights and encourage the use of daylight where possible.
  • A greater use of daylight and lighting controls in schemes is encouraged.

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