SIEMENS

A stroll after dark in the historic city center of Regensburg, Germany, raises a question. Do modern LED streetlights fit in harmoniously in the narrow medieval lanes of a World Heritage Site city? The light comes from quite a variety of lamps. Some alleys are bathed in a yellowish, almost otherworldly light. Then, just a few steps away, narrowly- focused light cones create a pattern of light and darkness on the cobblestones. Illuminating two of the narrow lanes are cylinders with many tiny points of light - lamps with light-emitting diodes (LEDs) developed by Osram Opto Semiconductors. The lamps were manufactured by Siemens in Regensburg and are designed to be screwed directly into the streetlight sockets. Up to 54 individual LEDs fit into one cylinder.

The warm light cast by LEDs on the city’s historic facades makes the city appear every bit as picturesque by night as by day. The alleys are also more brightly lit, with hardly any dark corners. That’s because many of the LEDs create long light cones along the narrow streets, while a few also focus light downward. The LEDs that light the opposite walls are adjusted to use only 30 percent of the electricity required for lighting sidewalks. This is another reason why the lamps require only 40 watts compared to the 90 watts required by their predecessors. "Another advantage of LEDs is that their light can be directed at specific points," explains Dr. Martin Moeck, Project Manager at Osram. "This isn’t possible with conventional lamps, so they often have to be overly bright in order to illuminate areas they otherwise couldn’t reach. LED lamps can focus their light more effectively, so they’re a lot more energy-efficient." Alfons Swaczyna, Head Construction Manager and Director of the Civil Engineering Office of the municipality of Regensburg, also likes the new lamps. "The LEDs have reduced light pollution, meaning light that used to glare into residents’ windows or up into the sky," he says.

Comfortable Color. LEDs stand out due to their high energy efficiency and their light’s excellent color reproduction. And they can do much more than conventional lighting. LEDs are immediately bright when turned on and can be continuously dimmed down to full darkness. With many other lamps, the gas discharge that produces light stops working if it drops below a certain level. And in the future it will be possible to automatically regulate the color of LED streetlights by, for example, mixing light from a white LED with that of a red one. All this makes the little diodes ideal partners for smart controls. Their longevity also makes them very attractive for municipalities. At over 50,000 hours of light, their service life is twice that of conventional lamps, and they need to be replaced only every ten years.

Energy-efficient street lighting has become an important issue in many cities - especially following the European Union’s regulation that in 2009 heralded the end of incandescent lamps. The regulation will also progressively phase out less efficient streetlight lamps by 2015, including widely-used mercury vapor lamps, which only deliver 50 lumens of cool white light per watt (lm/W). An alternative here is the high-efficency sodium lamp, which illuminates many highways with 120 lm/w. "However, sodium’s energy efficiency comes at a cost. The quality of light is inferior," says Matthias Fiegler, who is responsible for Osram’s global product portfolio for outdoor lighting.