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Flexible metal-halide uplighter for offices

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A new luminaire developed by the Swedish/UK-based lighting design company PELK and sold by the Swedish manufacturer Lyktan Lighting combines maximum flexibility with an original approach to office lighting. The new luminaire is used in two large, open-plan offices, one in Sheffield, UK, and the other outside Stockholm, the Swedish capital.

The luminaire is a metal-halide uplighter with a large screen and/or a small mirror to direct part of the light down towards the desk.

HIGHLY VALUED FLEXIBILITY
In the Swedish building, the large construction company Skanska turned a former warehouse into office spaces for a large international computer firm. Since the ceiling was high, 5 m above the floor, traditional indirect lighting could not be achieved. There, the 500 uplighters use a screen mounted on the luminaire that provides indirect lighting through a sort of individualized ceiling in each office space. Light straying beyond the screen helps to light up the ceiling 5 m above. Since the luminaire can be plugged into the wall socket without any hard-wired installation, the open office is very flexible.

Furthermore, each individual user can adjust the screen and luminaire placement to suit his or her own needs, and the switch is readily accessible. Since several hundred lamps are used in the area, relatively few are needed to light common areas. A general switch is used to control these lamps so that ambient lighting can be provided for the common areas.

To the Skanska project manager Svante Järnelo, the flexibility of the installation is important. "In fact, our tenant ICL consists of a number of smaller companies. We didn't get the furniture plans until a few weeks before our tenants were to move in. If we would have been forced to install all the lighting at that point, we could hardly have made it in time." Moreover, shortly after the tenants had moved in they shifted the furniture around again. Järnelo said that while the investments, including installation costs, were no higher than those for conventional, reasonably efficient lighting, operating costs are expected be lower. In addition, he pointed out that the increased flexibility is considered a very valuable asset, although this is hard to estimate in financial terms.

In the Sheffield office, the ceiling is lower, and only the small mirror of highly reflective Miro aluminum above the lamp is used. Here, a large part of the upward light passes the mirror and creates indirect lighting via the ceiling while also providing very high light levels at the desktop.

LESS FLICKER AND STABLE COLORS

Traditionally, metal halide lamps have not been favored by office lighting designers. One of the reasons for this is that the color of such lamps starts to shift towards the end of their life; another is that many people perceive them as flickering.

In the luminaire, a Philips 70-W Colorstar with an E27 screw-base and a 10-degree beam-spread integrated reflector has been used. The Colorstar lamp represents a new-generation of metal-halide lamps with the housing for the burner made out of ceramic instead of the usual quartz. The ceramic capsule prevents metal salts from wandering through the capsule, which causes the color shift in traditional metal-halide lamps. The lamp color is described as warm white at 3000 K (i .e., close to that of halogen filament lamps), and the spectrum is evenly distributed, enabling very good color rendering.

Another interesting development can be seen in the ballast design. Whereas typical metal-halide lamps operate at 50 Hz, this ballast operates at double the mains frequency. The ballast produces a square wave shape, which, in combination with the higher frequency, is enough to cut out the flickering often associated with metal-halide lamps. The manufacturer claims that the wave shape is very clean, reducing most potential problems of harmonics and interference with other electronic equipment in the building. Together with the ballast, the lamp has an efficacy slightly above 80 lumens per watt. The ballast/lamp combination draws about 80 watts, which is enough to provide a work place with both task and ambient lighting.

CREATING OWNERSHIP FEELINGS

Adrian Hallam, the architect responsible for the Sheffield project, says that preliminary results indicate that the installed power is less than 7 W m^2. But probably the most interesting effect has been on the behavior of office workers themselves, Hallam says: "The people at the office have started to regard the luminaires as their own, and they are very careful to switch them off when they leave their desk." He also adds that the luminaires create a room-like feeling around each person's desk within the large room and that they allow people to adjust the lighting to their own needs, even in cases where desks are situated close to each other.

Nils Borg

Contacts:

• Sven-Olof Berglund, Skanska Construction, Stockholm, Sweden
  Tel: +46 8 753 80 23
  Fax: +46 8 622 58 03
  
  
• Adrian Hallam, Adrian Hallam Architects, Sheffield, UK
  Tel: +44 114 268 4773
  Fax: +44 114 266 9191
  

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