# Design, Deployment and Evolution of Heterogeneous Smart Public Lighting Systems
## 1 Introduction  
As the world population grows at an ever-faster pace, with the majority of people living in urban areas, the idea of creating a more livable and sustainable city is becoming increasingly important. Projections show that by 2030 there will be more than 41 mega-cities worldwide (with more than 10 M people each), with a significant increase with respect to the current 28 mega-cities. Accordingly, the percentage of the population residing in urban areas is expected to reach 66% by 2050, compared to a figure of 54% in 2014 [1]. Since world cities already account for 75% of world energy consumption and contribute more than 80% to global greenhouse gas emissions [2], there are growing concerns about the availability and cost of energy, as well as about the environmental impact of its generation. Most likely, the solution (if any) to such issues will come from converging developments in several fields [3]: renewable energy sources, cogeneration, electric mobility, heating and cooling systems and lighting technologies, just to mention a few. Certainly, a key role will be played by Information and Communication Technologies (ICTs), which have created new opportunities to improve the quality of life in urban areas with intelligent and energetically efficient solutions. ICTs, through wireless communications and the Internet of Things (IoT) paradigm, will be transforming traditional cities into smart cities, providing the core infrastructure behind more efficient public services. This process has already started: in early 2018, China had about 500 smart city pilot projects [4], the highest in the world, and over 1000 smart city pilot projects were ready or under construction worldwide. In this framework, the momentum for smart public lighting is mounting, as several trials and large-scale implementations showed their effectiveness [5]. In particular, LED fixtures are expected to dramatically reduce urban electricity costs, now due to street lighting for a share of 40% [6]. Smart luminaires will dynamically adapt lighting to actual needs, for instance lowering the lumen output when there are low traffic volumes and good visibility conditions are detected. Important references in this regard are the \"GPP Revision of the EU Green Public Procurement Criteria for Road Lighting and traffic signals\" [7], authored by the Joint Research Centre (JRC) of the European Commission, and the CEN/TR 13201 lighting standards [8; 9; 10; 11; 12], which define how to properly design lighting systems. As reported in Reference [7], _\"due to the multiple benefits of dinming, dimming controls must be installed in all cases unless, in exceptional circumstances, it can be demonstrated that the total cost of ownership would increase by installing dimming controls. The EN 13201 standard itself [8; 9; 10; 11; 12] recognizes that the required lighting levels are dynamic in nature and an appropriate lighting level at all times can only be ensured with adequate dimming control during off-peak hours. Dimming has obvious environmental benefits via lower energy consumption and reduced light pollution. Furthermore, dimming can enhance the lifetime of LED luminaires due to a reduced risk of overheating, which is the principal cause of abrupt LED failure.\"_ In this regard, results from a global trial of LED streetlights show that, when coupled with smart controls, LED fixtures can deliver electricity savings of up to 80% over classic lighting technologies [13]. Beyond energy savings, since each smart streetlight needs to be provided with bidirectional communication capabilities, an ubiquitous city-wide communication network arises from the lighting infrastructure, reaching every location where a smart light fixture is present.