The development sector doesn’t exactly have a pukkah reputation when it comes to budgets, but the BREEAM Excellent-rated Angel Building in north London is firmly at the quality end.
Architect AHMM cites Mies van der Rohe’s Seagram Building and Tadao Ando’s Church of Light as inspirations, so you get the drift. ‘It’s a beautiful building, architecturally very clean and crisp,’ says lighting designer Mark Hensman of GIA Equation. ‘The lighting is tightly integrated into the architecture right the way through. Derwent is a very design-literate client.’
The project, a refurbishment and expansion of a 1980s building, is the largest office redevelopment in recent years. The emphasis on quality extends to the workspaces which have dynamic lighting, a Hensman hallmark – ‘I’d say that 50-60 per cent of what we do now has a daylight- mimicking, biorhythmic aspect to it’ – using Zumtobel’s Dali-controlled direct/indirect Freeline fittings with a Mode control system. Twin 35W T5s with two colour temperatures – 3000 and 4000K – cycle the lighting throughout the day.
Emphasis on quality
The ceiling height allowed suspended luminaires (Derwent was concerned not to compromise the original height of the main office spaces). The 2,300 fittings, notable for their pared-down lines, were installed in continuous rows of 3m extrusions with concealed end-to-end mounting.
With no suspended ceiling to hide the cables, luminaires had to accommodate all the power cabling for the entire run, in some instances up to 40m-long runs fed from one point. The office luminaires were chosen after four manufacturers equipped a full-size mock-up. ‘In my view, optically, in terms of the way they work light out of a luminaire, Zumtobel is among the best on the market,’ says Hensman. ‘They make a fantastic product.’
The key issue in the aim of creating a high-quality, low-energy working environment was dealing with the limitations of the original building. For one thing it doesn’t have a square footprint: the way it sits on the corner of the site means that one façade of the building curves, so fittings had to be made to custom lengths. More crucial was the lack of natural light.
‘The building is not naturally energy efficient in its floorplate layout,’ says Hensman. ‘We carried out extensive daylight studies at the beginning so that we knew what daylight values we were going to get in the space. We knew that because it was essentially a deep-plan office we were going to have to make the artificial lighting work quite hard.’
Installed vs operational
The installed load of the lighting is 15W/sq m – higher than might be expected because of the continuous design – but the operational load is about half that, at 7-8W/sq m, because the dynamic system is not using more than 40 per cent of the potential light output at any one time.
‘We knocked Part L into the middle of next week,’ says Hensman. ‘What I’m proud of is that, in an environment where we’re trying to get quite high light levels – 550 lux – in the middle of the office space to offset the lack of daylight – 40 lux with an overcast sky – we’re still getting those operational figures.’
Other energy-saving measures include daylight linking, and presence and movement detection. Where the ceiling heights are lower, nearer the atrium, lack of daylight ingress is countered with a brighter ceiling effect, using a recessed version of Zumtobel’s Lightfields microprismatic fittings – just under 900 – a sort of economic, quick-fix answer to the Barrisol approach. ‘There’s not a great deal of light coming in from the atrium so we knew that’s where the quality of daylight would be at its lowest, so we wanted planes of light on the ceiling,’ explains Hensman. ‘Lightfields was a natural option.’
Unusually in an office development, given the rigour of energy legislation, xenon is used in the entrance/atrium area along with cold cathode, metal halide and fluorescent. The warmer source helped answer a brief that called for a softer ambience in the atrium and reception areas.
‘Something we discussed a lot when designing the space was that it should feel like a hotel rather than an office building – a little bit more domestic, very comfortable and not cold, sterile or corporate,’ says project architect Steve Smith of AHMM. ‘It’s those sort of touches that soften it and make it have that hotel kind of atmosphere.’
It’s used for linear details where benches are recessed into the walls, for instance, and around the reception desk, while cold cathode is used for the integrated detail that wraps round the atrium. ‘The xenon is very limited and very targeted,’ says Hensman. ‘It’s in the intimate spaces, where you connect with the building – it’s almost like a reference to your table lamp at home. When you get to the bigger architectural presence of the atrium it moves to cold cathode and cooler, crisper colour temperatures.
‘The spec goes back three years,’ adds Hensman. ‘In time we will end up with an LED that will give us a tungsten-type dimming curve that will enable us to recreate that effect in a much more energy-efficient form.’
The aim of the lighting, says Hensman, is to create a tangible visual rhythm which leads people naturally through the building. ‘There’s a whole experience of approaching the building, from first seeing it right through to when you’re sat at your desk – that whole process is worked through. I think the building joins up that way.’ While public areas frequently take priority over the office spaces, at Angel the work spaces were high on the lighting agenda. ‘For me the office lighting is the most important lighting element in the building,’ says Hensman. ‘That’s where people are ensconced for eight hours a day. You want to get the whole building right but if there was a shopping list of what’s got to be perfect, top of the list would be the core office lighting.’