Efficient Lighting Stuttgart

Efficient Lighting

Stuttgart

Due to the impact of its lighting master plan, Stuttgart’s city centre is increasingly being seen in a “good light”. The planners who designed the concept attached great importance to aesthetics and the utilisation of technical advances for the controlled and energy-saving use of light. A prime example is Stuttgart’s new cylindrical luminaire, a fixture designed specifically by Hess for the state capital.

Stuttgart's new luminaire - Pleasant light at half the price

“The efficient use of electricity in public spaces is a major aspect in today’s light planning”, explains Klaus Volkmer, urban planner from Stuttgart’s urban planning and renewal office. At the end of the nineties, Volkmer initiated a process that eventually led to the creation of a lighting master plan for the City’s centre. Under the supervision of Stuttgart’s urban planning and renewal office, the basis for the lighting master plan was compiled by an interdisciplinary committee that included Uwe Knappschneider and his lighting design firm, Licht-Raum-Stadt, members of the City-Initiative Stuttgart, Stuttgart-Marketing, Kunstmuseum e.V., the City’s public works, the environmental protection office, EnBW (an energy utility company) and the State of Baden-Württemberg. Finally, at the beginning of 2006, the plan was approved and could be implemented as a planning instrument.
An energy- and cost-conscious concept
With the objective of the comprehensive lighting strategy being to improve the ambiance of the City’s centre, the plan pays particular attention to the areas that most lend the downtown area its distinct character, such as the pedestrian zones, characteristic architecture, plazas and parks. Citing the goals of the plan, Volkmer says, “Both the general lighting and the effect lighting should aesthetically enrich the nighttime environments of these areas, while providing security and improving orientation”. Each step in the realization of the plan involves an upgrading of aesthetic aspects and always the energy-conserving use of light, adds the urban planner.
The City’s new luminaire
Analysis had revealed that the existing lighting fixtures - globe-shaped luminaires designed specifically for the state capital in the seventies – had long failed to meet these modern demands. Due to the use of high-pressure mercury vapour lamps (approx. 47 lm/W) or in some cases even tungsten filament lamps (approx. 14 lm/W), the luminous efficacy of the old luminaires was relatively poor. The absence of optical elements resulted in glare on the one hand and undesirable nightglow on the other. In addition, the antiquated ballasts wasted a good deal of energy. For these reasons, the lighting master plan called for a new city luminaire, the investment costs of which would be paid for by the savings on electricity. Hess, a specialist for outdoor lighting products, had already addressed the subject of renewal and replacement with a new range of luminaires that met the principal aesthetic and performance specifications of the lighting designers while offering yet another attractive advantage. The luminaires mount on the already existing poles via an adapter, eliminating the need for pole conversion and wiring and thereby providing the City with added savings.

Electricity savings quickly pay for the investment

To meet the specific requirements of the City of Stuttgart, Hess worked closely with the lighting designers from Licht-Raum-Stadt to slightly modify their luminaire.
 Thanks to the use of 35-watt metal halide lamps instead of the 50- and 80-watt high-pressure mercury vapour lamps installed in the old globe-shaped fixtures, the new luminaires cut electricity use by 45%. Uwe Knappschneider, manager of Licht-Raum-Stadt and chief planner of the project, sums up the new lighting fixtures’ efficiency: “The new luminaires should pay for themselves within 20 years at the latest, which is before the end of their service lives.” In addition, the City is making a major contribution to the reduction of carbon dioxide emissions. Calculated based on the 45-watt reduction of lamp wattage and 4200 hours of operation, the savings amount to 189 kWh annually for each lighting unit. Multiplied by the 150 twin configured lighting units replaced up to now, the total power savings is 56,700 kWh per year. Moreover, the retrofit provides an environmental bonus, cutting annual carbon dioxide emissions by about 30,000 kg.

Precision-engineered optics reduce the number of luminaires required

The advanced reflector design provides significantly higher efficacy. Whereas the old globe-shaped luminaires wasted two thirds of their light output as stray light, only a mere 2% of the light emitted by the City’s new luminaire fails to illuminate the intended area or object. Regardless of the application, the new lighting system puts the light exactly where it’s required – whether street, walkway or plaza. For the City of Stuttgart, this meant that in many areas lighting units could be omitted. All considered, the electricity savings, compared to the old globe-shaped luminaires, add up to well over 50%. The electricity required to illuminate the Schillerplatz in the old section of the City centre is 57% lower since the new luminaires were installed according to an official City report. The elimination of lighting units also compensates for the higher costs of the HIT lamps and their maintenance.
Urban planner Volkmer views fewer luminaires as an aesthetic improvement: “Since the spaces are less cluttered, the facades, which lend the spaces their atmosphere, are free to unfold their unique character”. An example of this is the Schillerplatz. Surrounded on all sides by historical buildings, the plaza ambience has significantly benefited from a reduction in the number of luminaires, notes Volkmer. It was the first plaza to be furnished with the City’s new luminaires and it was the site where the different luminaire models were installed and initially tested. Old luminaires were directly compared to the new models. Explaining the sampling criteria, Volkmer says, “After the cost and the optimisati0n of the luminous efficacy, the next considerations were how the luminaires fit into the architectural context at night and during the day as well as the quality of their lighting”.

Easy installation

Hess’s luminaire scored well in all of the categories and impressed the city planners, particularly, due to its easy installation and maintenance. Compared to the old globe-shaped luminaires, which were mounted on brackets, the cylindrical luminaire mounts directly to the tops of the poles, increasing the lamp mounting height by 0.8 m to 4.5 m. “This produces proportional relationships between the luminaires and the urban architecture that are significantly more harmonious”, explains Volkmer.

Recognizably improved quality of lighting

The metal halide lamps provide excellent colour rendering, allowing the materials to appear in their genuine colours. Moreover, the advanced optical design provides pedestrians with extremely pleasant light that is largely free of glare. “The improved ambience and safety provided by the City’s new luminaires make a substantial contribution to Stuttgart’s attractiveness at night”, states Volkmer.