By Sara El Feky, Karl Göransson, Walter Longwe and Graham Mawer
There are more than 300 million street lights in the world and they are found on almost every urbanised street in the developed and developing world. A group of graduate students at Barcelona’s Zigurat Institute have been looking at whether this enormous infrastructure investment could be leveraged for more than just lighting. They have been considering whether the next wave in the evolution of street lights might involve the widespread addition of smart city sensors to the lights.
Street lights are ubiquitous, structurally secure, electrically powered and elevated over the roadway. Increasingly, as they are converted to LEDs, the street lights are becoming digital devices and are being paired with smart street lighting controls. Theis combination of characteristics make street lights a potentially ideal location to host additional smart city sensors at low cost. The sensors they could host might measure traffic, climate, pollution or noise parameters.
A key premise for the Zigurat project was that the street light may ultimately be the least expensive location to widely deploy sensors in the public domain. If a sensor can be directly plugged into a street light, installation labour costs will be low. No mounting bracket would be required and no additional power supply infrastructure would be needed (e.g, wiring, conduit, fuse, metering, metering box, surge protection). In some cases, where utilities own the lighting, placing sensors on lights may avoid complex pole access negotiations and charges for pole access.
The Pivotal Role of the Zhaga-D4i Standard
The Zhaga Consortium is an industry association of some 600 members that publishes industry standards for interfaces of LEDs and other components within lights. One of its industry standards, Zhaga Book 18, addresses the interconnection of components in outdoor lighting.
The Book 18 standard has progressively evolved to allow a two-node architecture where, for example, a smart control device can sit on the top of the street light and an additional sensor can be placed on the bottom of the light (see image). The sensor might be a motion sensor to help control lighting levels but it could also be a smart city sensor. Recognising the potential for street lighting to play a wider role as a piece of smart city infrastructure, the Zhaga Consortium staged an awards program in 2023 for Smart City Sensors.
The Zigurat project, while not affiliated with the Zhaga Consortium, recognised the pivotal role that Zhaga Book 18 and the D4i certification process is playing in shaping the future of public lighting.
Database of Zhaga-based Device Suppliers Released
While the market for Zhaga-based products is still relatively young, the Zigurat project has identified 41 suppliers globally offering Zhaga-based smart street lighting controls, motion sensors and smart city sensors. This database of suppliers containing contact details, classification of products offered and links to product pages has recently been published on Airtable.
Survey of Controls and Sensor Suppliers
The Zigurat project team used the database of suppliers to undertake a survey in mid-2024. About half the identified suppliers participated in the survey with 21 responses received.
One of the key survey questions focused on the international Zhaga-D4i product certification regime launched in 2021 in conjunction with the DALI Alliance. At the time of the survey, only 10 of the 41 suppliers identified in the project had chosen to certify one or more of their products. Of the survey respondents, 20% were not intending to seek certification or were unsure that they would while a further 43% said they were planning to or in the process of seeking certification. However, the rate of new certifications by suppliers who have not previously certified a device appears low in the public registry.
Based on the survey results and direct feedback from suppliers, the project team concluded that there was compelling evidence of hesitancy to certify new products by many suppliers despite the demonstrated marketing benefits of having certified products. The survey didn’t include end users and whether they valued the interoperability conformation that Zhaga-D4i certification offers.
The project team also looked at the communications approach being taken by the suppliers of smart city sensors. Zhaga Book 18 does not restrict how sensors communicate. Sensor data can be channelled via the DALI Bus in the luminaire and then transmit via the smart street lighting controls device to the Central Management System (CMS) for the lighting controls provider. However, by not restricting how sensors communicate, the Zhaga standard also allows sensors to communicate independently. 63% of survey respondents who sold smart city sensors said that they were either communicating independently via communication chips in their sensors (e.g., via NB-IoT or LoRaWAN) or preferred to communicate independently given that Zhaga Book 18 does not restrict the choice of communications approach.
Based on the survey results and direct discussions with suppliers of smart city sensors, the project team concluded that trying to channel general purpose sensor data via the DALI Bus and out to a street lighting CMS was proving challenging for some suppliers. The path of least resistance for many suppliers was to include a communications chip in their sensor and send the data directly to their own CMS or to a general smart city platform.
In terms of device costs, the survey results indicated that 75% of smart street lighting controls providers and 63% of motion sensor suppliers were selling their devices for less than 100 Euros. Costs for smart city sensors were much more varied, ranging from below 100 Euros to 600 Euros. The project team concluded that the early stage of the market for these smart city sensors, the lower volumes and the complexity of some sensors were the likely root causes of the wide range of pricing.
The final survey question focused on the motivation for suppliers to develop Zhaga-based devices. An overwhelming 86% of survey respondents cited the street light as being a good location for many sensing tasks while 71% said that their customers were asking for the devices. In terms of cost, 48% of suppliers believed that the street light-based sensors were less expensive for their customers to purchase and deploy while 43% said that they were less expensive to produce than other sensors. From the responses, the project team concluded that there appeared to be a widespread industry view that the street lights are indeed a good location for many sensing tasks and that customers want the devices.
Conclusions
An ever-wider array of Zhaga-based smart city sensors is continuing to emerge but some barriers remain to widespread adoption. Based on the relatively slow rate of certifications and the evident preference of suppliers for using independent communication technologies, the Zigurat project team concluded that there would be advantages in more overtly promoting that Zhaga Book 18 does not restrict how sensors communicate and that sensors which communicate independently can still meet all certification requirements. Overall, cities could benefit from both greater Zhaga-based sensor choice, from sensors which are compatible with their existing IoT networks and from the increased confidence and lower risks which comes with more sensors being independently certified.
The project team also recommended that there be further studies monitoring Zhaga-D4i adoption, development of more case studies about early adoption, economic analysis quantifying the benefits of widespread use of street lights for hosting of smart city sensors and made a series of recommendations about greater stakeholder engagement.
