KNOWLEDGE
The changing face of office lighting

Jon Dale, managing director of Phi Lighting, asks how we can meet the conflicting demands of guidance, regulations and changing technology in our projects

Jon Dale

We must not repeat the mistakes of the past

Despite the increasingly rapid changes in the luminaire supply market, there are constants that drive these changes. Looking to these constants guides us for the future.

Lamp and computer screen technologies, ceiling system trends, modern materials and manufacturing methods, and the study of how the use of space changes create an equation of opportunity for lighting to solve.

The incorporation of modern LED technology creates opportunities to more easily meet the requirements of legislation and energy economy but should come with a caveat if we are not to repeat the disastrous mistakes of the 1980s and 1990s Cat 2 tidal wave.

Lest we forget

Cat 2, lest we forget, begat the most unpleasant working conditions, with oppressively dark ceiling and wall luminances and huge diversities of luminance in the near field. The Cat 2 solution was driven by the very same drivers we face today – energy, legislation, efficiency and screens. Some of the luminaire designs we have seen recently are similar – with high direct ratio, open cell solutions common to both. This is a concern.

There are further potentially conflicting parameters that the lighting designer must endeavour to navigate safely. For example, we see Cibse guidance for offices asking us to consider the luminance balances for wall, ceiling and working plane to create pleasant working environments for people.

High utilant lumens

However, the Building Regulations demand high utilant lumens per circuit watt delivered to the working plane for the purpose of legislation (utilance is the proportion of luminous flux emitted by a luminaire that reaches the working plane).

The added layer of lighting control offers sophistication and the chance to adapt space to the changing physiological needs of users through changes to vector, volume and colour. There is an apparent disharmony between these elements.

How, for example, with the still relatively high cost of LEDs and their monodirectional output, are we to create pleasantly illuminated ceilings and upper wall surfaces? How will we attenuate the particularly high luminance of the LEDs themselves? How will people perceive such ‘bright’ sources, especially in peripheral vision, and what can be done about this? What can be done to prevent veiling reflections in screen technology?

Careful practice

The answers are in the careful practice of lighting design and luminaire technology. There are several differences now compared with the 1980s and 1990s that help with some answers.

Materials technology for lenses and optics has facilitated the effective attenuation of luminance at critical angles above the vertical to reduce peripheral glare to occupants and reflections in screens.

This is further possible without compromising the very high light output ratios that are critical to meeting legislation.

The ability to change the colour of LED sources further enhances the comfort and mood of employees and in all probability their efficiency as well.

My own experience also identifies that designers have learned the lessons of the past and are now more ready to use more than one type of luminaire to achieve the desired effect, even in the most cost-driven projects.

So although modern optics can do much to diffuse bright objects, they are still not refracting light back to ceilings.

This leaves us with a choice. Use direct-indirect fittings that would multiply the cost by two if they use LED sources, or argue that the luminaire luminance contributes to the overall ceiling luminance, which it does, but conveniently misses another fact – the ceiling luminance is meant to be delivered with as little contrast as possible.

Best avoided

This is not possible when a luminaire has 1,500-3,000cd/m2 and offers no light back to the ceiling. Our view is that such high contrasts are best avoided.

Equally, we recognise that this is not easy when solutions are driven by ceiling types and the need to provide value solutions. That said we have some interesting ideas and luminaires for the future which go towards meeting these needs.

Who said it was easy?

● Phi has a free lunchtime presentation titled Lighting for People, Planet and Project that tries to distil the apparent disharmony between these objectives into simple, sensible practice. Visit www.phi-lighting.com for details.

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