Photo: DTU

Mobile service for the street lights

Monday 04 Apr 16

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Henrik Chresten Pedersen
Senior Researcher
DTU Fotonik
+4546 77 45 50
Street lights with LED bulbs have to be checked and adjusted, as their light intensity decreases over time. DTU researchers have now come up with a smart method for handling the service procedures.

LED is the new trend when it comes to street lighting, and with good reason: LED lights are both energy-efficient and durable. The only problem is that they cannot be relied upon to provide illumination of the same intensity throughout their service life, which can be as long as 15 years. As a result, they have to be adjusted continuously, and two DTU researchers have now come up with a maintenance method with the potential to eliminate thousands of working hours for the light owners.

The way LED lights age is defined by various factors, such as the ambient temperature and how efficiently the fixtures conduct heat away from the bulbs. That makes the ageing process so difficult to predict that it is impossible to programme the lights to adjust themselves, and fitting a sensor to them is not a viable solution either: any such sensor would gradually become dirty and unreliable.

Instead, it has to be possible to measure the illumination from a vehicle and remotely adjust the lights—or so thought Henrik Pedersen, Senior Researcher at DTU Fotonik, who teamed up with Henning Larsen, Senior Development Engineer, to develop a system comprising a light sensor mounted on a service vehicle and a communication module installed in the lights themselves.

The communication module is a small electronic component about the size of a box of matches, which can be set to flash at a frequency invisible to the naked eye. Every light has its own unique flashing frequency and is registered in a database along with its GPS coordinates.

On a signal from the service vehicle, all the lights in a given street begin to flash, and the vehicle then drives under each light, calculating the level of illumination as it passes and sending a message to each light to increase or decrease the illumination intensity as appropriate.

The company HeSaLight has bought ComLight—the patent taken out by Henrik Pedersen and Henning Larsen—and renamed it TrueLight. The invention has quickly proved its worth in connection with a major order for 30,000 lights for a project in Chile, where one of the requirements from the customer was that the installation should be validated. This would take 2,000 person hours to complete manually, but can be done in less than 50 hours using TrueLight. 

How TrueLight works

Photo: DTU

Light no. 1 flashes at a frequency of 1000 Hz, light no. 2 at 1005 Hz, light no. 3 at 1010 Hz, and so on. The sensor in the vehicle then uses these frequencies to identify the individual street lights.

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