# Design and Application of a Smart Lighting System Based on Distributed Wireless Sensor Networks
## 1 Introduction  
Energy saving for buildings has been attracting widespread interest as the building sector is considered the most energy-consuming sector, which consumes over half of global electricity and over one-third of the overall energy [1]. The International Energy Agency predicts that the energy demand of buildings will increase by 50% by 2050 if certain measures are not conducted to improve building energy efficiency [2]. In buildings, lighting systems constitute a large proportion of energy consumption. For instance, lighting accounts for 11% of the consumed energy in residential buildings by end-use in the United States [1] and 21% of the consumed energy in commercial buildings in the United Kingdom [3]. In China, the largest growth in energy end-use in commercial buildings occurred due to the demand for lighting [1]. Hence, it is vital to develop new strategies to achieve energy saving for lighting while satisfying the illumination comfort of users. Advances in smart technologies have brought in a new generation of building energy behaviors and control approaches, where smart lighting system has a direct impact on energy saving, user's comfort, health, and safety [4, 5]. Compared to the traditional lighting system based on manual on/off switching, the smart lighting system leverages advances in light-emitting diodes (LEDs) and information and communications technologies (ICTs), such as wireless networks and sensors, to create efficient and healthy illumination [6, 7]. Using various information, such as occupant presence and available daylight,both of which can be acquired by sensors [8; 9; 10; 11], and user preference set by building users [12; 13], LEDs can be controlled automatically and efficiently by a digital input signal. Further energy saving can be realized by optimizing LEDs' dimming levels with the objective of minimizing the power consumption of all LEDs subject to illuminance constraints [14]. However, in real applications, for instance, in commercial buildings and public facilities, the lighting is dynamic because people move randomly. As a result, optimization models have become sophisticated, time-consuming, and require high-performance hardware. The development of a smart lighting system in real application faces three main challenges. First, due to a large number of luminaires to be controlled and the importance of lighting to people's health and safety, a smart light system is complex and demands a short time delay. Second, a balance between system performance and the life-cycle cost is required. The life-cycle cost consists of designing, manufacturing, and maintenance costs. Generally, the more precise the system control is, the higher the life-cycle cost will be. However, the performance may not increase proportionally with the cost. For instance, the closed-loop lighting controller does not contribute to visual performance optimally [15], and the energy savings it achieves is less than that achieved by the open-loop controller in [PERSON]'s experiment [16], although the former has more accurate tuning of artificial light output than the latter. Third, compared with a wired lighting control system, a wireless system is easier to deploy and more attractive for retrofitting the existing lighting controls with minimal disruption; however, new problems can arise in wireless systems, such as higher communication traffic, larger delays [9], and underillumination [17]. Considering these challenges, this study proposed a smart lighting system that can be implemented in different types of buildings, such as office buildings, parking garages, and subway stations. The proposed system includes luminaires, sensors, a distributed wireless sensor network (WSN), and a rule base for lighting control. Each luminaire is equipped with a sensing module that controls the dimming level considering the illuminance value of daylight, occupant presence, and schedules.