# Design and Application of a Smart Lighting System Based on Distributed Wireless Sensor Networks
## 4 Results
### Scenario 2: Company Office  
The second test scenario of the proposed smart lighting system was a 1399-m\({}^{2}\) multifunctional office located on the 4 th floor of a building at Ningbo city, China. The floor plan of the office and the layout of luminaires are presented in Figure 13. The requirement for illuminance on the work plane was 500 lx. All luminaires were LEDs, and their types, power, and numbers were listed in Table 6. Each luminaire was equipped with a wireless sensing module. The maximum sensing distance was set to 2 m. As shown in Figure 13, the largest office room highlighted with red lines was selected for the experiments, and the control strategy for smart lighting depicted in Section 3.3.1 was used. Zones A, B, and C in the control strategy are depicted in Figure 14a. In this case, Zone A included a leisure space in the upper left corner and an area for printing in the upper right corner. Office cubicles were placed in Zones B and C. Moreover, 62 line lights and 6 downlights were used in Zone A, B, and C. The locations of the PZ and SZ of Zone B for daylight harvesting are shown in Figure 14b. The ambient light sensor was deployed in the LED that was the nearest to the windows. The illuminance value of the light sensor was about half of the illuminance of daylight on the desktop right below the light where the sensor was located. The control rules were defined by Equation (3). The performance of daylight harvesting was correlated with the weather condition. The distribution of the dimming levels of luminaries at 10:00 a.m. in 2 days corresponding to two types of weather conditions, i.e., clear sky and overcast sky, are presented in Figure 15a. Compared to the overcast sky, under clear sky conditions, there were more LEDs with lower dimming levels. As shown in Figure 15b, the values of the light sensors exceeded 180 lx in more than 65% of the working hours during the day time, which was from 9 a.m. to 6 p.m., which indicated that the dimming levels of LEDs were 30% in the PZ and 70% in the SZ; in contrast, the values of the light sensors were between 125 and 180 lx in about 45% of the working hours and less than 125 lx in the rest of the time. Although the daylighting was good under a clear sky, most of the luminaires were dimmed to 100%, as shown in Figure 15a. There were two reasons for high dimming levels. First, Zone A and 45% of worktables in Zone B were in the middle of the floor plan, where the daylight condition was poor. Second, the requirement for illuminance on the desktop was 500 lx leading to a small PZ. If the requirement of illuminance was reduced to 300 lx, the new PZ could be expanded to the same size as the old secondary zone, and the SZ could be expanded too. Figure 13: Floor plan and layout of luminaires: (**a**) floor plan of the office and (**b**) layout of luminaires, each of which was equipped with a sensing module. The power consumption of the proposed smart lighting system was evaluated and compared with that of the normal lighting system where lights were switched on manually at the beginning of the day, i.e., when the first worker entered the room, and switched off at the end of the day, i.e., when the last worker left the room. The power consumption was calculated under the assumption that the power consumption of each LED was proportional to the dimming level collected by the gateway in every 15 s. The power consumption from 8 a.m. to 10 p.m. in 1 day is shown in Figure 16. The overtime was after 6:30 p.m. in the evening. As there was a need to use neighboring luminaires to meet the required illuminance value of 500 lx, luminaires were turned on even when they were unoccupied, but their neighbors were occupied. Therefore, from 9 a.m. to 6 p.m., the power consumption of the proposed system was relatively stable, and the power savings were low, as shown in Figure 16. Moreover, about 70% of the staff stayed after 6:30 p.m. With the decrease in the staff number in the office, energy savings owing to the occupancy detection increased.