PROJECTS

The answer to the energy challenge at building company Hanson’s new corporate HQ in Bedfordshire was to cut lux levels by nearly half. Richard Brass reports

With an ambition from the client to achieve a Breeam rating of excellent, the energy-saving potential of lighting was always going to be vital to building materials company Hanson’s plans for its new HQ in Stewartby, Bedfordshire. But even so, the designer’s solution came as something of a surprise.

‘The client took a bit of convincing,’ says Dave Robinson, director of lighting design consultants Pinniger. And it’s no surprise. With conventional offices typically lit to around 400-450 lux, Pinniger’s proposal to create an ambient level of just 250 lux may have seemed a riskily bold step.

Ambient lighting consumes just 4.38W per square metre

Ambient lighting consumes just 4.38W per square metre

But the convincing worked and, following the development of samples and a working mock-up, the design went ahead, enabling the building to produce a remarkable energy consumption figure of just 4.38W per square metre for the ambient lighting. This is augmented by task lighting at individual workstations, itself a way of ensuring that light is only used as needed and keeping energy use down.

Beyond the ambient and task lighting, Pinniger made the best use of the large amount of daylight provided by the design of the new building. ‘The reduced ambient level and additional task lighting goes hand-in-hand with the massive ingress of daylight from all four elevations of the two main wings of the development,’ says Robinson. Detailed AGI modelling and stereographic sunpath diagrams were produced to verify the design.

Raft luminaires act as dampers for any sound in the space

Raft luminaires act as dampers for any sound in the space

‘It was pretty critical that there was a daylight- linked control system that needed to be implemented to ensure that you could maximise your savings through the natural ingress of daylight contributing towards the task lighting where required.

Daylight-linked control

‘The lighting above the desks closest to the windows is on a daylight-linked control system which allows for the lights to dim down when there is sufficient daylight, to achieve the required working illuminance. Where there’s an ingress of daylight, the lights are dimmed down significantly, which allows for additional energy savings.’

As well as the daylight-linked controls, the building features a series of occupancy sensors, ensuring that lights will be switched off when there are no staff in a particular area of the footplate.

Daylight, artificial ambient light and task light work together

Daylight, artificial ambient light and task light work together

For more than a century, Stewartby was the site of a quarry and brickworks, and elements of the new building were designed to mirror that heritage, with tall brick pillars running along a large part of the building. Uplights were used at the base of these pillars to highlight the feature and add to the effect.

Pinniger also came up with an innovative approach to the building’s stair cores. ‘The way in which the visual appearance on the outside of the stair cores was achieved during hours of darkness is that normal bricks were supplemented with acrylic bricks,’ says Robinson. A full mockup was manufactured on site to ensure that the correct lit effect was being achieved.

‘So during hours of daylight you have natural ingress of daylight coming into the stairwell, and there is little need for artificial lighting within the stairs. Then at night, when you illuminate the stairs from within, the building sparkles when viewed from the outside where you see all these pinpoints of light.

Those are not individually lit. They’re purely picking up ambient light within the stairwell.’

Artificial lighting supplements the ambient light sources and daylight

Artificial lighting supplements the ambient light sources and daylight

To achieve its low-lux ambient environment, Pinniger needed to produce a bespoke fitting to deal with the specific challenges of the space. ‘Because it’s a large, open-floor-template concrete structure which, if fitted with a standard luminaire without any acoustic properties, would be very echoey, there had to be an embellishment on the luminaire,’ says Robinson. ‘The way in which we decided to do it was to design special luminaires but incorporate acoustic properties into the raft so that it would act as a dampening for any reverberating sound in the space.

‘The fitting itself was a bespoke design developed with Luxonic. It was a 28W T5-type fitting with an acoustic panel in it. In essence it was a suspended direct/indirect fitting with an SAS acoustic ceiling tile incorporated within the body of the luminaire. We used the standard SAS acoustic tile on either side of the actual luminaire, which gave it its acoustic properties.

‘It depends very much on the architecture of the building. In this particular case it didn’t have a ceiling, and you went straight up into the coffers of the structure, which is always a challenge to light without causing a lot of hot patches on the ceiling. You want to use a direct/indirect to actually enhance whatever reflective surfaces you’ve got on the ceiling, so there was a challenge in that as well.’

Times change

The task lights used were small compact fluorescent desk lights, but Robinson says that if the project were to begin now, there would probably be far more LED. ‘This was developed in 2006/07, when LED was very much in its infancy in terms of usable products on the market. If we were faced with the same brief today the products would be significantly different.’ The trend towards lower ambient light levels

and greater use of task lighting, however, has strengthened since the Stewartby project began, and Robinson believes it is the way forward for office lighting. ‘It’s something which we are pushing for,’ he says. ‘We’re dealing with another client where they’re doing a very similar exercise in terms of reducing ambient levels and using dedicated lighting in breakout areas to emphasise the key elements within the space as well as task lighting in areas of importance above desks. It’s something that we would always try to encourage because of the ability to reduce energy consumption.’

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