Tunnel lighting solution based on embedded system and LED lamps

At the Copenhagen World Climate Conference, Premier Wen Jiabao pledged on behalf of China that by 2020, the ratio of carbon dioxide to GDP would be reduced by 40% to 45% from the 2005 level. China is mountainous, with mountainous areas accounting for 2/3 of the country's total area, which brings great inconvenience to transportation construction. By the end of 2009, there were as many as 6,139 highway tunnels in the country, including 190 extra-long tunnels and 905 long tunnels. The electricity consumed in tunnel lighting is quite huge. For this reason, we conducted research on highway tunnel lighting methods.

1. Essentials of tunnel lighting design

During the day, when a driver approaches, enters, or passes through a tunnel from outside, if there is no lighting in the tunnel, the entrance will appear as a "black hole" and the exit will appear as a "bright hole" due to the huge difference in brightness between the inside and outside of the tunnel; when a driver enters or passes through a tunnel with a lighting system at night, the situation is just the opposite. These phenomena will cause safety accidents. For this reason, the "Highway Tunnel Ventilation and Lighting Design Specifications" has formulated relevant specifications, and made detailed provisions on the brightness of the entrance section, transition section, middle section, and exit section. The relevant regulations are as follows:

1) Entrance section brightness requirement Lth (cd/m2)

Where k is the reduction factor, L20 (S) is the brightness outside the cave (cd/m2)

2) Brightness requirements during transition

The brightness Ltr1 of lighting segment TR1 is as follows:

The brightness Ltr2 of lighting segment TR2 is as follows:

The brightness Ltr3 of lighting segment TR3 is as follows:

3) The middle segment brightness Lin, as shown in Table 1.

Table 1 Brightness specifications for the middle segment

4) Exit section brightness.

The brightness is 5 times that of the middle segment.

Night lighting is controlled at two levels: when the traffic volume is large, the brightness is equal to the middle section brightness Lin; when the traffic volume is small, the brightness is 0.5Lin but not less than 1 cd/m2.

2 Design solutions for LED smart lights

2.1 Comparison between LED intelligent lighting and traditional lighting in tunnels

1) Traditional tunnel lighting solutions

In order to save energy, traditional tunnel lighting solutions usually adopt four levels of lighting, namely sunny, cloudy, overcast and heavily overcast. This control method generally controls the number and position of lights to achieve the purpose of graded lighting. The lamps used are also traditional high-pressure sodium lamps. Since the power of high-pressure sodium lamps is only 100 W, 150 W, 250 W and 400 W, and many highway tunnels only need 40~120 W for basic lighting, the basic lighting of tunnels is usually 100 W, 150 W or higher high-pressure sodium lamps [3]. There are generally problems of over-lighting or manual control.

When designing the power of lamps, a certain maintenance factor must be considered to ensure that in actual operation, when the brightness of the lamp light source decays and the lamp is polluted and the brightness drops by more than 30%, its lighting intensity can still meet the requirements of the specification.

The Highway Tunnel Ventilation and Lighting Design Code stipulates that the maintenance factor is 0.7. For example, if a tunnel actually requires an 80 W lamp, then the lamp power must be at least 115 W during design. At the same time, it must be considered that the lamp will wear out over time. In order to ensure that the lamp meets the design specifications, there must be a certain amount of redundancy, generally 1.7 times. Therefore, the lamp power must be higher than 136 W during design, so a 150 W high-pressure sodium lamp is selected.

2) LED smart lighting solutions

LED has the characteristics of high luminous efficiency , long life and easy control. For example, if a tunnel actually needs 80W lamps, it can be controlled to 80W specifications with LED smart lights to avoid over-lighting. The brightness of LED lights in the tunnel is intelligently controlled according to the brightness outside the tunnel, especially the brightness adjustment of the entrance section and transition section. That is, the brightness of the section is designed according to the designed driving speed of the tunnel, and the lighting fixture is controlled to be as bright as possible (LED smart lights must also have a certain amount of redundancy) to avoid over-lighting, which can save energy and reduce pollution emissions.

2.2 LED simulation lamp design

As shown in Figure 1, a 24 W simulated tunnel lamp is made of 1 W Taiwan Jingyuan pure white light high-power lamp beads; the Darlington control circuit is used in the lamp control system, so that the LED lamp beads in the experiment reach the best brightness (110 lm); the standard luminous flux of the simulated lamp is 2500 lm (Tj=25℃), and the maximum luminous flux reaches 7500 lm (Tj=60℃, Ta=25℃).

Figure 1 Simulated tunnel light

3 System Design

3.1 LED Smart Light Circuit System Solution

This scheme is designed with two sets of control circuits, one to control the brightness of the LED light group, and the other to control the brightness of the lamp. The research team installed a brightness monitoring device outside the simulated tunnel to convert the natural light intensity into a 0~5 V DC voltage signal, which is then analyzed and calculated by ARM 7 (stm32f103vc, central controller ) to control the brightness of the LED lamp to meet national standards (segment brightness control instructions); at the same time, a brightness monitoring device is also set up in the simulated tunnel to collect signals and analyze and calculate the brightness of the corresponding road section in the simulated tunnel. If the brightness is insufficient, the brightness of the corresponding LED lamp is automatically adjusted to increase, so as to achieve intelligent supplementary lighting, so as to effectively compensate for the weakening of the brightness caused by lamp loss or dust, exhaust gas and other factors.

3.2 Segmented lighting control design

Oncoming vehicle detection Sensors are set at equal intervals as shown in Figure 2. D1 is a sensing belt at a distance from the tunnel entrance. When a car reaches D1, the signal collected by D1 is transmitted to the central controller for processing, and then the D2→D3 section light group is lit; when the car reaches D2, the signal collected by D2 makes the D3→D4 section light up; when the car reaches D3, the D4→D5 section is lit. At this time, if there is no car passing through the D1→D3 section, the D2→D3 light group is turned off; the subsequent light groups are controlled by the same principle. This solution is used in highway tunnels with less traffic, and the energy-saving effect is more obvious. If the solution can be promoted, it will save a lot of electricity for the country and make a huge contribution to China's energy conservation and emission reduction .

Figure 2 Segment control sensor setting method

3.3 Energy consumption comparison

This paper takes the Qianlingshan Highway Tunnel in Guiyang City, Guizhou Province, the longest municipal tunnel in Asia, as an example to illustrate the energy-saving advantages of this design scheme. The tunnel is 1,580 meters long, with a designed speed of 60 kilometers per hour and uses high-pressure sodium lamps for lighting.

Entrance section: 90 m long, with three lamps arranged in groups, spaced on both sides, each lamp has a power of 150 W, and the distance between lamp groups is 5 m.

Transition 1: 30 m long, with groups of three lamps and groups of two lamps arranged alternately, symmetrically on both sides, each lamp has a power of 150 W, and the distance between lamp groups is 5 m.

Transition 2: 70 m long, with two lamps in a group, arranged at intervals on both sides, each lamp has a power of 150 W, and the distance between lamp groups is 5 m.

Basic 1st section: 610 m long, one lamp per group, arranged at intervals on both sides, each lamp has a power of 150 W, and the distance between lamp groups is 10 m.

Basic 2 sections: 750 m long, one group of lights on the right, 10 m between groups, each with a power of 150 W; one group of lights on the left, lit at intervals, 10 m between groups, each with a power of 150 W.

Exit section: 35 m long, with three lamps in a group, arranged at intervals on both sides, each lamp has a power of 150 W, and the distance between lamp groups is 5 m.

Based on the basic situation of the tunnel, for the convenience of calculation, the high-pressure sodium lamps are arranged at intervals of 10 m on both sides for analysis, so there are at least 300 lamps on both sides of a single tunnel. The power of the tunnel high-pressure sodium lamp is 150 W; in order to meet the design lighting requirements, it is necessary to consider a certain amount of redundancy, maintenance factor, and the clear width and height of the tunnel building limit, the rated luminous flux of the lamp, etc. The design adjustment range of the LED smart lamp is 80~130 W. According to the "Highway Tunnel Ventilation Lighting Design Specification" and the actual measured brightness data of the tunnel, the "average value of 90 W is calculated" is used in actual use. Without changing the layout of the lamps, the annual energy consumption of the high-pressure sodium lamp and the LED smart lamp is compared as long-lasting lamps, as shown in Table 2.

Table 2 Comparison of energy consumption between high pressure sodium lamps and LED smart lamps

As can be seen from Table 2, using LED lamps for 24-hour lighting can reduce energy consumption by 60%. Based on the electricity price of 0.30 yuan/kWh, this section of the tunnel alone will reduce the lighting electricity cost by 47,000 yuan per year. Based on the current traffic volume passing through this section, if the "lighting when there are cars passing, turning off when there are no cars" lighting plan is implemented, energy consumption can be reduced by at least 25% (turning off the lighting for 1/4 of the time). If this plan is promoted for highway tunnel lighting across the country, it will have good economic benefits for highway operating departments and significant social benefits for the national energy conservation and consumption reduction strategy.

4 Conclusion

This solution is based on the actual situation of western tunnel lighting. The lamps designed combine embedded systems and LED lights, which not only make the lighting intelligent and digital, but also have stable performance and reliable operation. At the same time, the use of segmented control technology instead of traditional whole-segment control technology has obvious advantages in energy saving, providing a new reference for future tunnel lighting solutions.