Light:Guard GmbH has implemented a pilot project for demand-controlled night marking (BNK) at the Danish wind farm Sønder Bork. Over a period of six months, the light:guard system reliably detected flying objects and documented how often the obstacle lighting could have been switched off under the applicable Danish framework conditions. The evaluation shows a theoretical light-off time of 97.4 % with a system availability of 98.7 %.
BNK reduces the flashing of wind turbines to a minimum. To do this, the system monitors the airspace around a wind farm. When a flying object approaches, it cancels the suppression of the lighting and the red light flashes as before.
In Denmark, the law that allows the obstruction lighting on wind turbines to be switched off as needed is still in the draft phase. Therefore, the project was initially operated exclusively in report mode. The lighting of the five turbines remained switched on, and the shutdown was simulated virtually.
For this purpose, Light:Guard installed a Light:Guard receiver (LGR), which detects transponder signals from flying objects. While the receivers in German wind farms are usually installed at a height of 80 to 175 meters above ground, the receiver in Sønder Bork could only be installed at ground level. The antenna was attached to the outside of the transfer station at a height of about five meters. According to current knowledge, this is the lowest receiver installation for BNK in a wind farm worldwide.
Among other things, the Danish requirements provide for the detection of flying objects from 300 feet, i.e. around 91 meters, above ground. The pilot project was therefore also a test to see whether such a low-mounted receiver can detect aircraft at the required minimum altitude. This has now been proven to be the case.
“Not the first and certainly not the last pilot project that I was able to accompany and even install personally. The installation of the receiver close to the ground was particularly unusual,” says Light:Guard hardware specialist Heiko Nöldeke. “The fact that the system runs so smoothly and reliably detects flying objects makes me all the happier.”
Usually, in addition to the receiver, a Light Control Unit (LCU) is installed in each wind farm to control the lighting in the wind farm. Since this could not yet be legally suppressed by the BNK system, Light:Guard developed a virtual Light Control Unit for the pilot project.
This virtual LCU prepared the recorded data for reporting. This made it possible to track how often the system was available and how long the flashing could theoretically have been suppressed.
The Light:Guard receiver was installed on March 4, 2026. Light:Guard put the system into operation on March 9, 2026, and since then it has been recording the transponder signals of flying objects in the vicinity of the wind farm.
For the analysis, the data from six months from March to September 2026 were evaluated. The light:guard system achieved an availability of 98.7%. The theoretical light-off time was 97.4% on average. The proportion of theoretical light-on time and errors that occurred was minimal.
Sales agent René Aamand has not only accompanied the legislation in Denmark for three years, but also the Sønder Bork project: “With this case study, it was possible to show that the light:guard system works reliably even under these special conditions: in a new regulatory environment, with an unusually low receiver installation and according to the detection requirements intended for Denmark. Now we hope that the law will be passed soon so that the nights can also get dark in Denmark.”
The case study thus provides a reliable data point for the planned introduction of demand-driven night marking in Denmark. This is not far away: the Danish authorities are working on the final draft law, which is to be adopted at the end of the year.
Light:Guard is ready for this: “As soon as the law allows BNK in Denmark, we will turn the turbines at Sønder Bork wind farm dark, together with another wind farm. We hope to be the first in Denmark,” says Felix von Hammerstein, Head of Business Development at Light:Guard, hopefully.
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