Xiaoyan: LED tunnel lighting and optimization

Why do tunnels need to be set up?

The lighting of the road tunnel is to transmit the necessary visual information to the driver to prevent traffic accidents caused by insufficient visual information, thereby improving driving safety and increasing comfort.

At present, tunnel lighting designers usually design the lighting by dividing the tunnel into four sections: the entrance section, the transition section, the middle section and the exit section.

Figure 1: Tunnel brightness curve

According to the "Code for Design of Ventilation Lighting for Road Tunnels", the brightness of the exit section is 5 times the brightness of the middle section. Looking at the illumination curve of the entire tunnel, why is the brightness of the entrance and exit sections so high? That's because the car has a "black hole" and "black box" effect when driving into and out of a tunnel with unreasonable lighting effects.

Black hole effect - before the car enters the tunnel, the brightness of the sky in the driver's field of vision, the open road, the nearby buildings, etc. is much higher than the brightness of the tunnel entrance. Although the hole actually has a considerable brightness, the driver still feels the hole is very Black, like a "black hole", can not identify the situation near the hole, even obstacles are difficult to find.

Black frame effect - Before the car exits the tunnel, the brightness outside the tunnel exit is high, and the brightness inside the tunnel is very low, which causes glare at the exit due to excessive contrast. If there are obstacles in the shadow around the tunnel, it is often difficult to identify or even detect. Since the shadow resembles a "black frame", this phenomenon is called the "black box" effect, which is likely to cause serious traffic accidents.

Current status of tunnel lighting:

The length and illuminance (lx) of each segment are based on the annual driving safety requirements. The design of the maximum illumination in the hole is to determine the lamp power and the distribution density of the lamps in each section of the tunnel with the maximum brightness and maximum speed of the year. . The ability to achieve automatic lighting control is very limited, usually due to the limitations of the wiring circuit, only 2 or 3 manual or automatic control (day: sunny, cloudy, cloudy, heavy), for such as speed, traffic flow, etc. The parameters are only given to the maximum value during the design phase, and finally the length and illumination of each segment of illumination are always at their maximum. Time-varying parameters such as vehicle speed, traffic flow, and CO ₂ concentration cannot be adaptively modulated from the macroscopic illumination of the entire tunnel.

Therefore, there is a large amount of power waste problem in the tunnel lighting system of the conventional design and use.

Through the investigation of the operation of tunnels in Shanxi, Shaanxi, Zhejiang, Sichuan and Chongqing, it is found that the electricity and ventilation expenses of highway tunnels are a large number. For example, the Yanmenguan Tunnel on the Shanxi Dayun Expressway has a total electricity cost of nearly 300,000 yuan per month. The total length of the Nanshan Highway Tunnel is 36km . The monthly lighting cost is more than 2 million yuan. These are undoubtedly the tunnel management departments. The huge economic burden.

——Xia Yongxu, Highway Tunnel Lighting Problems and Countermeasures

Tunnel lighting optimization

 

1, lamps and light sources

The light source adopts American CREE high-efficiency LED, and the lamp adopts reasonable heat dissipation structure design and lens design to distribute light evenly.

LED characteristics:

(1) High luminous efficiency . The theoretical value of LED light efficiency can reach 240lm/W, and it has reached 120lm/W or above. The color rendering is high and the light has a strong directivity.

( 2) Energy saving and environmental protection . LED is a cold light source, semiconductor lighting itself does not have any pollution to the environment, compared with incandescent lamps, the power saving efficiency can reach more than 90%. Moreover, the LED is a green light source, which is driven by DC, has no stroboscopic, and has no radiation pollution.

(3) Flexible design. The light-emitting chip is small, close to the point source, convenient for optical design, combined with the brightness of the LED and the adjustability of the color temperature, so that the LED has more advantages in designing the lamp than the conventional light source.

Table 1 : Comparison of pre-construction and 6- year operating expenses of LED lights and high-pressure sodium lamps in Qianyiping Tunnel

The left and right lines of Qianyiping Tunnel are 926 meters long, one-way and two lanes, and the lighting design calculation speed is 60Km/h.

——China Traffic Information Industry, 2007 , Issue 11 , page 34

It can be seen from the table that although the LED tunnel light has an initial investment of 36,300 yuan more than the high-pressure sodium lamp, due to its low power consumption and maintenance-free, the LED tunnel light can save at least 5,076,400 yuan after 6 years of use. The author gives this example to illustrate the economic benefits of using LED. If you want to investigate its future light decay and longevity problems, I think it should be further studied from the following two aspects:

• The quality of light sources, the global LED industry is mainly distributed in Japan, Taiwan, Europe, America, South Korea and China and other countries and regions. Moreover, the US and European countries have mastered the core technologies of upstream epitaxial wafers and chip manufacturing. Packaging is China's main R&D and application field. However, among the LED-related listed companies in China, there is still no listed company with packaging as its main business. From this point of view, the quality of LED packaging is still uneven in the domestic market;

• The efficiency of the driving power supply, the tube voltage drop of the LED changes with temperature, which requires constant current driving of the LED. Constant current drive is an important parameter to measure the quality of a drive power supply. It is also a prerequisite for ensuring the long life of the LED. In addition, the LED drive power supply preferably has overvoltage, overcurrent protection and soft start functions.
• Radiator performance, high-power LED will generate a lot of heat during normal operation, and the excess heat will be exported in time to improve the service life of the LED. This depends on the heat dissipation performance of the heat sink. Many of the tunnel lamp heat dissipation designs do not take into account the air convection problem, which causes the heat to not be actually exported, reducing the LED life.

2, intelligent controller

The intelligent controller is used to networkize the tunnel lights, and the brightness of each LED tunnel light is updated according to actual needs. On the basis of the use of LED tunnel lights, the intelligent control method is adopted to make the brightness of each road section timely within the scope specified in the "Code for Design of Ventilation Lighting of Highway Tunnels", thereby avoiding excessive waste of electric energy.

The intelligent controller also has the following features:

(1) It has rich external interfaces: CAN, RS485 and IIC, which can be connected to the network through CAN, and the nodes can reach 2^32 to realize network control;

(2) It has a soft start, which eliminates the impact on the electronic device and the light source caused by excessive current during the startup, and prolongs the service life of the light source;

(3) Integrated non-volatile memory to save system operating parameters in real time and with data verification function to ensure the correctness of each parameter for each power-on;

(4) With the fast calculation speed of DSP, the controller detects the current, voltage and temperature of each LED in real time, and has self-protection function of overvoltage, overcurrent and over temperature, and automatically alarms;

(5) With high-precision clock, it can accurately record the error occurrence time (can be accurate to the second). The date and time can be set by the host computer broadcast;

(6) The controller itself automatically restarts;

Electrical isolation characteristics: The communication line and the system are electrically isolated, and the system has strong anti-interference ability.

Figure 2: System outline frame

Figure 3: Intelligent controller framework in the tunnel

Figure 4: Tunnel Light Host Computer Control Software Interface

summary

Driven by the concept of energy saving and emission reduction and low carbon economy, the LED industry is getting more and more attention. How to better apply LED has become a topic of discussion. This article aims to explore the application of LEDs in tunnel lighting.

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