Anyone walking through the Musikerviertel district of the municipality of Maxdorf in the late evening will notice a change: 25 streetlights are shining in new light. In February 2019, the old mercury vapor lamps were replaced with modern LED lighting modules. However, this alone would not be a special feature according to Michael Heidinger, who works as a research associate at the KIT Light Technology Institute (LTI): "Many municipalities are currently converting their streetlights to light-emitting diodes, or LEDs for short. In doing so, not only do they comply with European requirements regarding environmental toxin avoidance, they also enjoy many benefits. LEDs offer a service life of up to 50,000 hours, are energy-saving and enable more uniform illumination."
The special feature of the new luminaires in Maxdorf, however, can only be seen on closer inspection: Instead of a few, strong high-power LEDs typically used in streetlights, they use so-called mid-power LEDs. These are smaller and lower-light diodes characterized by increased energy efficiency and reduced glare. "However, to achieve the same luminous power, mid-power LEDs must also be installed in larger numbers, which leads to problems related to an increased operating voltage," explains Heidinger.
Since the voltage increases proportionally to the number of diodes connected in series, mid-power LEDs reach high voltages very quickly. The safe touch voltage of 120 volts is quickly exceeded. To get around this, the LEDs would have to be connected in parallel. However, a parallel connection has so far resulted in an uneven distribution of current to the individual LEDs, which not only leads to strong differences in aging, but also, in the event of failure of a single diode, to the failure of the entire system.
This is precisely where Heidinger's novel circuit technology comes in, ensuring even current sharing for mid-power LEDs. "One current regulator per parallel-connected LED string ensures that each string is regulated to an average value determined in the circuit. In the event of deviations, differences are adjusted," Heidinger said. "This now enables the use of mid-power LEDs in large-area, high-lumen applications."
The great potential of the patented circuit also meets the expectations of Klaus Müller. As managing director of GRATZ Luminance GmbH, a luminaire manufacturer in the premium segment, sustainability is clearly in focus for him.
GRATZ Luminance is working on long-lasting lighting solutions in the joint project "Optimized Overall LED Luminaire System," in which the LTI is also involved. "We developed our LED luminaire module based on Mr. Heidinger's circuit. By significantly increasing the efficiency, we can set ourselves apart from the competition without having to compromise on service life," Müller clarifies. "This allows us to save up to 30 percent potential power consumption savings compared to high-power LEDs of the same generation."
The idea is also finding fertile ground among users: "We consider the technology to be extremely promising and have gladly agreed to test the luminaires in a field trial," explains Stefan Lang, Technology and Innovation Manager at Pfalzwerke AG. 25 street lamps in Maxdorf are now equipped with Gratz luminaires and will be tested thoroughly over the next two years. To this end, measuring devices have been installed to record the performance of the luminaires. "This will allow us to evaluate the results in a few months and convince other communities to use mid-power LEDs," says Lang.
There are a large number of potential applications, ranging from lighting for company grounds and campuses to bike paths. "We are eager to see the results of the field trial to substantiate the excellent efficiency with a long lifetime with practical figures," Heidinger says.
"It makes me proud to see the result of years of research in Maxdorf. We also get positive feedback from the residents, who feel much safer thanks to the improved lighting."
Images: dailin / Shutterstock, bearbeitet von DER PUNKT · Tanja Meißner / KIT