In Regensburg, OSRAM Opto Semiconductors and Siemens have demonstrated that energy-saving LEDs can provide authentic period-style lighting for a historical centre. The companies have developed a retrofit solution which meets the requirements of a modern lighting system while preserving the atmosphere of a world heritage site. The light sources being used are Golden Dragon Plus LEDs. Discreetly installed in the luminaires prescribed by the Office for the Preservation of Historical Monuments, they target the precise spot they are intended to illuminate, thus avoiding light pollution.

Regensburg has narrow alleys and many winding streets in a multitude of different lengths and widths. And this is why the intricately structured town needs luminaires which enhance its historical ambience. To ensure consistently attractive lighting, the different colors of the buildings must be taken into account and the kind of use, color temperature and color rendering index adjusted accordingly. The street lights must not be dazzling in residential areas, for instance, nor should they spoil the romantic atmosphere of candle-lit restaurants.

With its retrofit prototype, which is based on the Golden Dragon Plus LED, OSRAM has come up with an option that truly fits the bill. The light is fully directed to the exact place it is intended to illuminate: to the street, or also to the façade, when it is used to highlight architectural features. And the desired level of illuminance and the light distribution can be precisely adjusted by adapting the number, the optical devices and the dimming of the LEDs. The LEDs have a color temperature of 3500 K and a color rendering index of 80. A common optical device combines the light from the individual LEDs into a single beam and accurately directs it towards the desired target. As part of this project, the alleyways known as “Blaue Liliengasse” and "Untere Bachgasse" were fitted with new luminaires and some of the LEDs were selectively directed towards the façade. This ensures that the lighting can be precisely tailored to the architecture.

The prototype luminaire permits the replacement of ordinary 90 W mercury vapour lamps with LEDs. The luminaire design is based on a cylinder. Manufactured by the Regensburg branch of Siemens, the prototype can be fitted with different numbers of LEDs on either side as required and so as to produce the desired lighting effect. This allows for completely different light distributions. Up to now, there was an uneven distribution of light, but now a homogenous illumination of around 3 Lux has been achieved. "We have achieved the same illuminance while cutting energy consumption from 90 W to just 42 W and additionally integrating façade illumination for historical buildings," said a contented Dr. Martin Moeck, Project Manager for Application Concepts at OSRAM Opto Semiconductors, "And there has also been a marked reduction in the direct glare."