# Comparative Study of Energy Savings for Various Control Strategies in the Tunnel Lighting System
###### Abstract
The solutions adopting LEDs and integrating sensors and communication technologies enable lighting control systems to become smarter with greater sensing, data processing, and connectivity. [PERSON] et al. [35] proposed an energy-saving tunnel lighting control system where the LEDs operate in continuous low-power mode when there are no vehicles in the tunnel. In this condition, the energy consumption can be as low as 10% of the maximum power. When a vehicle's approach is detected, the inside tunnel luminance is determined by vehicle speed, traffic level, and ambient luminance. [PERSON] [36] proposed an intelligent tunnel lighting control system that sets the LEDs' luminance to the lowest level of CIE-88 standard when the vehicles are not inside the tunnel at night. Otherwise, the tunnel is divided into 10 lighting groups. The luminance of the two groups' LEDs in front of the car is increased when the vehicle enters the next group, with the other groups maintained in tunnel-saving mode. [PERSON] et al. [37] constructed an energy-saving fuzzy tunnel lighting control system based on IoT (Internet of Things) technology. There are three input variables (L: real-time exterior environmental luminance, V: vehicle speed, and N: traffic volume) and one output variable (the real-time luminance of sodium lamps) in this fuzzy system, which have five, five, three, and 75 linguistic levels, respectively. [PERSON] et al. [38] implemented the fuzzy logic control system used an FIS (fuzzy interface system) in MATLAB software. In this system, the inputs are the sun location, weather conditions, and the year's season, while the outputs are luminous intensity and color temperature. Moreover, the sun position has nine different cases (night, early morning, sunrise, morning, noon, afternoon, sunset, evening, and again, night), the year's season has two cases (summer, winter), the luminous intensity has 11 cases (0, 10, 20,... 90, 100), and the color temperature has five cases (candle, warm white, daylight, cool light, and blue sky). [PERSON] et al. [39] proposed a no-cost finetuning method for switching lighting stages based on the traffic weighted L\({}_{20}\) luminance to minimize lighting consumption in existing tunnels. Total energy consumption and the corresponding energy savings for four scenarios were examined. The results showed that the energy saving could reach 54% when replacing existing lamps with LEDs. Most current tunnel lighting systems changed from outdated conventional lamps to state-of-the-art LED lamps without modifying the position and quantity of the existing lamps. This change resulted in significant energy savings and provided opportunities to further increase savings by automatically regulating the luminous flux according to different circumstances [40]. Moreover, as mentioned above, various luminance control strategies have been explored for LED technology. However, few studies guide the reader on selecting the right lighting control strategy based on tunnel length and traffic volume. This paper compares the performance and energy-saving potential of various lighting control strategies based on the SCADA (Supervisory Control and Data Acquisition) tunnel lighting system. Eleven tunnels in China with different tunnel lengths and traffic volumes were examined. Then, we provide suggestions on how to select a lighting control strategy for various scenarios.