# Design, Deployment and Evolution of Heterogeneous Smart Public Lighting Systems
## 4 Economic Analysis  
In this section, we discuss the economic benefits that can be achieved transforming a traditional lighting infrastructure into a smart one. In absolute monetary terms, costs and possible savings vary from one country to another. However, according to our experience, the relative contribution of each cost item (e.g., electricity, maintenance) to the overall cost figure is approximately the same all over the world, so as the possible savings that can be achieved introducing smart features. For this reason, in the following we will express such savings as a percentage of the yearly operational cost, maintenance included, of a traditional non-LED fixture. According to [73], this cost can be broken down as follows:  
* 70% for the cost of electricity, computed assuming 4200 lighting hours per year per each streetlight and 130 W traditional lamps. * 30% for maintenance operations, computed taking into account the costs of manpower (50%), the use of specialized vehicles (30%) and materials (20%). **Retrofitting with LED luminaires. Expected saving. ** In terms of energy consumption, simply replacing traditional luminaires with LED ones leads to a significant saving. In fact, a 130 W non LED lamp is equivalent, in terms of lighting intensity, to a 70 W LED one. Thus, a 46% saving in terms of electricity cost is achieved by simply replacing the luminaire, which means (considering the overall electricity+maintenance cost) a 32% saving per year per each fixture. This estimation, confirmed also by [13], is prudential as several papers claim that higher reductions in energy cost can be achieved [64; 74]. In particular, [PERSON] et al. published a report on 106 test-beds from 17 European countries, showing an average energy saving of 59% compared with that of the original installation [5]. **Light fixture remote monitoring. Expected saving. ** Additional savings can be achieved introducing an LC capable of both monitoring in real-time the lamp functioning (lamp status and electric parameters) and transmitting collected data along with the pole ID to the Control Center, which can timely infer or predict failure conditions. This allows both to prevent malfunctions (e.g., when a defective power supply poses a lamp in a stress condition) and to optimize failure recovery operations. In fact, broken lamps can be timely detected, along with their positions, so that repair teams can be dispatched according to a well-planned scheduling, also taking into account the best route to fix all failures in the same area. The amount of saving provided by improved maintenance practices is hard to estimate,as it depends on how maintenance is locally managed. It is expected, however, that it is in the order of a few percentage points per year per streetlight. **Light dimming. Expected saving. ** Making the LC also capable of dimming LED lights leads to two more benefits. On the one hand, this feature enables the luminaire to follow daylight variations, meaning that the light intensity can be \"tuned\" with a fine time granularity to compensate variations in natural light at the sunset and sunrise, thus avoiding the energy wastage caused by a simple on/off policy [75]. On the other hand, the dimming profile can be easily adjusted over the years also to compensate the unavoidable luminous flux degradation due to luminaire aging. As anticipated in Section 3.3, dimmable light sources, such as LEDs, allow the implementation of the CLO functionality, which provides further energy saving. The economic benefit of light dimming depends on many factors, such as the luminaire Wattage, the adopted dimming profile and the daylight duration. Nonetheless, several trials showed that a reduction of 40%\(\sim\)45% in energy consumption is a realistic target [76; 77], which leads to a 15%\(\sim\)17% saving per year per each fixture. **Dynamic dimming. Expected saving. ** Further economic benefit can be achieved introducing a dynamic, context-aware, lighting control mechanism.