Adaptive Smart Street Lighting – Infrared (PIR) Sensor vs. Radar Sensor

Adaptive street lighting refers to street lights that adjust illumination to movements by pedestrians, cyclists, and vehicles. Adaptive smart street lights automatically brighten to a preset level only when a human is detected in the vicinity. If there is no one around, the street lights remain dimly lit. As a result, energy is saved, light pollution is lowered, and carbon footprint is minimized. All these without compromising public safety.

There are two types of adaptive street lighting systems available today – Infrared or PIR (passive infrared) sensor-based and radar sensor-based system. The Münster University of Applied Sciences carried out a pilot project to determine which system – PIR or radar – is more practical to select for large-scale projects.

From Stadt Münster:

Pilot project with Münster University of Applied Sciences

The ongoing innovation in the field of technical road equipment – especially in lighting technology – presents new challenges for decision-makers when it comes to determining the time and type of future-oriented investments in 28,000 light points in Münster. In the field of public street lighting, innovative solutions can save energy costs. The Office for Mobility and Civil Engineering shows how this can work in the future.

Whether and to what extent the environment can be relieved by measures taken by the City of Münster’s Office for Mobility and Civil Engineering in the area of street lighting was intensively discussed and worked out in the past with the Münster Municipality and the Münster University of Applied Sciences. As a result, a pilot project was carried out in which two adaptive street lighting systems were examined for their practicability in order to be able to select the most suitable technology for future large-scale projects.

The most important goal of the pilot project was to be able to maintain the high level of road safety while saving energy at the same time. In addition, Münster’s civil engineering department is striving to maintain the first place it achieved in the audits conducted by the North Rhine-Westphalia Municipal Auditing Institute, among other things through this project, and to put new technologies to the test as a pioneer in street lighting. Infrastructure projects in public spaces in particular are in the focus of the public, as they have a direct impact on the mobility habits of users. Experiences gained by road users with the new system will be incorporated into future projects.

Münster is one of the cities with the highest volume of bicycle traffic in Germany, which is why a pilot project was implemented on a footpath and cycle path in the city of Münster.

Sensor technology for tailor-made lighting

The city of Münster is already using the modern sensors in traffic control, such as cyclist counts and traffic lights. In many areas, sensors enable the flow of traffic to be tailored to the needs of road users.

In street lighting, the sensor technology makes a major contribution to saving energy, for example by reducing the light intensity on paths with low night-time traffic.

The decisive factor for use is the error-free, weather-independent detection of road users. It is intended to ensure traffic safety through effortless seeing and being seen, while at the same time guaranteeing the sense of security of road users through an appropriate level of lighting, especially in areas with little social control.

In order to analyze whether these goals can be achieved through the use of sensors, a 680 m long pedestrian/bicycle path was selected as a test track. This opens up both a school center and a shopping center and also has a connecting function. The straight course with few entrances (parallel railway line) provides ideal test conditions, as the detection ranges of the sensors are relatively easy to calibrate. In addition, the framework conditions for both systems are the same over the entire test track, which simplifies the comparison. Seven lights with radar sensors are used in one section of the test track and twelve lights with infrared sensors in another section. Inexpensive sensor technology was used here to enable future projects in the field of adaptive street lighting.

Test Evaluation

As soon as the volume of traffic decreases (e.g., when the shopping center closes), the recordings only show occasional switching at night. By using the sensor system in the street lighting on the pedestrian/bicycle path, energy savings of 70% could be achieved. Further advantages are the individual circuits (single light point control) and the possibility of monitoring the operating status of the lights.

The test results in terms of road safety and susceptibility to errors are very different.

The infrared system works reliably in this application, regardless of weather conditions. However, faulty switching caused by small animals is present and apparently cannot be completely avoided despite the appropriate calculation algorithm. The individually adjustable detection areas can be easily adapted to the prevailing conditions. Road users are regularly detected regardless of their speed.

The radar system used in the course of the pilot project also works regardless of the weather. However, the radar sensors react to unwanted Doppler signals caused by trees and bushes moving in the wind. Careful positioning must therefore be carried out outdoors and the vegetation cut back, which incurs operational maintenance costs. In addition, faulty switching by small animals is also possible here.

The radar sensors need to be improved so that the lighting does not dim up at slow to medium walking speeds. In view of the large number of older road users and the associated desire for accessibility, street lighting must also react to slower road users. However, due to their design, radar sensors only react at speeds of approx. 2.8 km/h, which is why they are less suitable for sidewalks than infrared sensors.

Adaptive street lighting provides users with a partially higher, needs-based lighting level within a moving light honeycomb. This immediate reaction to the user supports the sense of security.

Survey of road users

It is important to involve the public in infrastructure projects (especially with innovative components). Therefore, on the one hand, information was provided on site with the help of information boards, the press and the city’s homepage, and on the other hand, the impressions and experiences of the users were surveyed online and on site over a period of four months. This allowed road users to test and evaluate both systems under different weather conditions.

Users rate the systems as very reliable and consider the burn time and system response to be balanced. The illumination and visibility provided is found to be good and the overall sense of security has also been increased. Only slower road users criticized that the lights were sometimes dimmed or the sensors did not even trigger.

Overall, the survey results were positive. The benefits of the systems (such as resource efficiency and improved social security) were recognized. The city’s willingness to test new technology on a test track was also widely praised.

The negative, critical comments make it clear that users also notice and question small things. Two important conclusions can be drawn from this: On the one hand, it is advisable to set up an accompanying, comprehensive information concept when introducing adaptive lighting. On the other hand, the careful setting of the sensor areas and light durations is of great importance for a positive perception. As in other areas of traffic planning and technology, the principle applies here that the infrastructure must be comprehensible and self-explanatory for users. Faulty switching and poor sensor settings lead to irritation and reduced acceptance.

In addition to the user survey, the impressions of the residents were also evaluated. The majority of these are neutral to positive in relation to adaptive lighting. The sense of security increased, although nocturnal switching errors were noticed.

Positive balance

Basically, the sensors were able to convince both in terms of user perception and error analysis. Other areas of application for adaptive street lighting, such as residential and commercial areas, are planned for 2018. Here, however, the detection areas are much more complex, which requires further investigations.

Regardless of the selected system and the general conditions of the route section, it is recommended to set the sensors and calibrate the parameters very carefully and to have the functionality checked by inspections and tests.

Overall, the balance is very positive, so that the city of Münster will use adaptive street lighting for newly planned footpaths and cycle paths.