# Design and Application of a Smart Lighting System Based on Distributed Wireless Sensor Networks
## 4 Results
### Scenario 1: Metro Station  
The proposed smart lighting system was implemented in an underground metro station in Nanjing, China. This station consists of a concourse level and a platform level. The simplified floor plan of the concourse level with 276 luminaires is presented in Figure 9. Each luminaire in the level was equipped with a wireless sensing module except in zone 2, which was used as a comparison zone in the energy-saving tests. Zones 1 and 2 were symmetrical and had the same geometry size and number of luminaires. The difference between zones 1 and 2 was that zone 1 utilized the smart lighting system, while zone 2 used the normal lighting system. Under these conditions, the experiments were conducted for 1 month without any interruption, demonstrating high robustness and reliability of the proposed system, including sensing modules and ZigBee networks. The occupancy and dimming-level data were analyzed to evaluate the occupancy detection performance of the proposed system and to investigate the impact of passenger flow on energy saving when the proposed smart lighting control is used. The PIR activations recorded by one sensor node (number 18) in zone 1 during 3 days are shown in Figure 10, where high occupancy can be observed between 7 a.m. and 9 a.m. and between 5 p.m. and 8 p.m., which was caused by commuting needs. The metro station was closed from midnight to 6 a.m., and in that period, inspection and maintenance work were carried out by the staff, which can explain occupancy detections before 6 a.m. in Figure 10. As passengers were mainly commuters and there were not many other passengers who used the station for leisure or tourism, the PIR activations were low in the other time periods. The distributions of PIR activations met the characteristics of people flow in the station. Figure 8: Two walking scenarios with lighting control strategies: (**a**) walking straight forward and (**b**) passing an intersection. Beyond the brightened area, the light-emitting diodes (LEDs) are at the dimming level of 10%. The comparison of dimming levels of a luminaire in zone 1 under different people flow densities with respect to a luminaire in zone 2 is presented in Figure 11. The lighting control strategy depicted in Section 3.3.2. was used in zone 1, and zone 2 utilized a normal lighting system without occupancy sensors in which luminaires were at a 100% dimming level during the metro operating time and most of them during the metro nonoperating time. Three types of people flow densities were considered: low density, medium density, and high density. As shown in Figure 11, with the decrease in the people flow density, the proportion of time when the dimming level was 10% increases. A higher dimming level indicated greater energy consumption. Thus, the higher the proportion of 10% level was, the more the energy savings were. Hence, the energy savings were inversely proportional to the people flow density. Accordingly, two conclusions can be drawn as follows: (1) based on the occupancy detection data presented in Figure 10, the largest energy saving occurred between 11 p.m. and 7 a.m., followed by time period from 11 a.m. to 3 p.m. and (2) the smart lighting system should be preferentially installed in metro stations with small passenger flows in order to save more energy. In order to evaluate the proposed system in terms of power saving, the comparison experiments were conducted in two zones, which had the same geometry size and number of luminaires except for the deployment of the smart lighting control system. Each zone was further divided into two subzones, of which one had 10 LED luminaires, and the other had 13 LED luminaries. One luminaire has two LED tubes, and the specifications of luminaires are listed in Table 4. After the installation of the proposed system in zone 1, the energy consumptions of the four subzones were measured in  
Figure 10: PIR activations in a 24-h period. Figure 9: Deployment of the proposed system in the concourse level of the metro station.