In the new century, the state has increased the construction of transportation systems, such as railways, highways, expressways, high-speed railways and so on. Tunnel lights must be installed in the tunnel, which leads to the large-scale LED tunnel light industry.



     LED tunnel light has incomparable advantages of traditional light source tunnel light, energy saving and environmental protection, high brightness, high color index, long life, small size easy to install, especially high power LED tunnel light, no matter the brightness or service life is far beyond the traditional sodium lamp tunnel light, is the current mainstream tunnel light products. Let's compare LED tunnel lights with traditional tunnel lights.



1. Comparison and selection of functions between conventional tunnel lights and LED tunnel lights



     At present the traditional tunnel lighting are mostly using high pressure sodium lamp as light source, but high pressure sodium lamp in the form of radiation, color rendering, visual sensitive features, specifications, brightness control power are many deficiencies, and new LED tunnel lights, especially in high power LED tunnel lamps and lanterns with its superior performance, especially the controllability of brightness, overcome the disadvantages of high pressure sodium lamp, in today's world is becoming the mainstream of tunnel lighting lamps and lanterns. The state also introduced a new measure of "ten cities and ten thousand lights" semiconductor lighting project, which brought unprecedented opportunities for the development of LED tunnel lights. In order to actively respond to the "ten cities ten thousand" plan, zhongshan yuexen lighting has invested heavily in introducing advanced LED tunnel light production equipment from Europe, and vigorously developed and produced new LED tunnel lights. At present, LED tunnel lights occupy a decisive market share in China.



     Leds (light emitting diodes), or leds, are a type of semiconductor light emitting technology. The earliest LED can only emit red light, which is used for indicator lights in electronic devices. With the development of technology, now LED lights have been able to send all colors of light, and is widely used in many sectors, main application markets including traditional display and light market, back light, LED street light, LED tunnel lights, car lighting market, the outdoor landscape lighting and indoor decorative lighting, special lighting market. LED as a tunnel light source has its unique advantages.



     (1)LED tunnel lamps consume less power and save energy. Compared with high-pressure sodium lamps, they save more than 60% energy.



     (2)LED tunnel lights have a long service life. Take luna lighting high-power LED tunnel lights as an example, their normal service life is more than 60,000 hours, which is more than 10 times the service life of sodium lamps.



     (3)LED tunnel lights have good working stability and are basically maintenance-free during use, while sodium lamps have very high maintenance cost in the later stage.



     (4) reduce the construction cost of power distribution system (cable, transformer, distribution box, bridge, etc.). In the case of long tunnel and long-distance power supply, cables and distribution facilities account for a large proportion of the cost. The use of LED tunnel lights can greatly reduce the investment in cables and distribution equipment due to power saving.



(5)LED tunnel lights can be started instantly, which is convenient for brightness adjustment. With the advantages of no strobe and wide starting voltage range, it can realize various energy-saving methods, such as intelligent adjustment of illumination according to the traffic flow of roads and tunnels. Lunshen lighting new LED tunnel lights can also achieve remote control, time-sharing control and other intelligent control.



     (6) high pressure sodium lamp, fluorescent lamp, infinite lamp contain mercury, lead and other chemical pollutants, while LED tunnel light source does not contain chemical pollution substances, is the green environmental protection light source. Luna LED tunnel lamp has been certified by European standard ROHS. Environmental protection is the prerequisite for entering the European market.



     2. Design requirements of high-power LED tunnel lights



     (1) basic lighting should be set in the tunnel no matter it is daytime or night. When the vehicle enters the tunnel in the daytime, the brightness of the road surface should gradually decrease, so that the vision of the driver has an adaptive process. The entrance section is divided into the introduction section, the adaptation section and the transition section.



     (2) determine the length (S) of the introduction segment, the adaptation segment and the transition segment. Usually, according to the vehicle speed (V), the adaptation time of T=2s is determined, and S=VT/3.6m can be used to estimate. The exit section shall also be provided with transition lighting, the same as the entrance section in two-way traffic.



     (3) there is no enhanced lighting at the entrance and exit at night, and street lamps should be installed outside the cave, whose brightness should not be less than 1/2 of the basic brightness inside the cave; Tunnel should be equipped with emergency lighting, its brightness not less than 1/10 of the basic brightness.



     (4) according to the provisions of China jtj026-90 highway tunnel design code, the length of tunnel entrance lighting interval and the minimum pavement brightness standard shall be designed according to the requirements as shown in table 1.



     3. Design scheme of high-power LED tunnel lights



     3.1 selection of LED light source



     LED single tile lumen output is to determine whether LED tunnel light has the practical value of the basic indicators, according to the requirements, LED tunnel light leds used on the number of single tile lumens should reach more than 100 lumens, after nearly three years after LED luminous efficiency of the high speed development, the present stage luna lighting can supply large quantities of LED lights has amounted to more than 120-130 lm/W, and the brightness is also in constant increase. Table 2 provides the main technical parameters of high-power 1W white LED with mass production on behalf of the most cutting-edge international manufacturers. OSRAM manufacturer LUWW5AM can be used as the design light source. With the characteristics of LED light source with different color temperatures to choose from, the LED light source with similar color temperature of 4000~6000K to sunlight can effectively reduce the "bright hole" and "black hole" effect.



     3.2 light distribution design



     According to the lighting requirements of the tunnel, different lighting distribution lamps are adopted according to different lighting segments. According to the optical principle and the characteristics of high directivity of LED light source, reasonable lighting distribution is adopted to reduce the power of the lamps and achieve the purpose of energy saving while meeting the requirements of brightness or illumination. Luna's latest LED tunnel lights adopt transverse lighting distribution, which is more suitable for the narrow and long road lighting in the tunnel.



     (1) the introduction of the tunnel entrance section, to adapt to the segment and transition section and export section using asymmetric illumination light distribution (back lighting), under the condition of same illumination, compared with general lighting, can improve the surface brightness 121%, at the same time, the use of the advantages of high directivity, strictly control the direction of large Angle of light intensity, eliminate most glare.



     (2) at the basic section of the tunnel, the common distribution patterns of light distribution include concentrated light distribution, lateral light distribution, lambert-type light distribution, etc. Different application of different forms of light distribution, for example: road lighting should choose the bat wing type light distribution, spotlights should choose the spotlight type light distribution. Due to the particularity of tunnel lighting, the arrangement density of lamps in tunnel lighting is very high, so the secondary light distribution form of lamps in tunnel lighting is different from general road lighting. In tunnel lighting, bat-wing lighting and lambert-type lighting can meet the requirement of uniformity of illumination, which is mainly due to the small lamp distance in tunnel lighting. Figure 1 shows the C0 direction lighting pattern of two LED tunnel lights. The left side shows the bat-wing lighting pattern commonly used in road lighting and tunnel lighting, and the right side shows the lambert-type lighting pattern. The use of bat-wing lighting, that is, the wide light band symmetrical lighting, under the same illumination condition, compared with ordinary lighting, can improve the brightness of road 64%, improve the uniformity of road brightness.



     3.3 heat dissipation design



     LED is a photoelectric device. According to the high-power LED at the forefront of the world, only 15%~20% of the electric energy is converted to light energy in its working process, and most of the rest of the electric energy is converted to heat energy, which increases the temperature of LED. On the other hand, LED lumen output decreases with the rise of LED junction temperature, while LED life shortens with the rise of junction temperature. Therefore, the LED heat dissipation treatment is directly related to the use effect and life of tunnel lamps.



     At present, there are three main ways of heat dissipation of high-power LED: (1) natural heat dissipation, add fan forced heat dissipation and heat pipe plus fin technology, etc. Natural heat dissipation makes use of natural convection and thermal radiation, reliable structure, easy to do waterproof, but high requirements for the structural design of the lamp body itself. (2) add fan forced heat dissipation mainly by forced convection, heat dissipation speed is fast, but the cost and noise is high, difficult to do waterproof. (3) heat pipe plus heat fin technology is mainly used to heat pipe LED heat quickly conduction to heat fin and achieve the purpose of heat dissipation, no moving parts, the system is stable, but the cost is relatively high.



     Because compared with the general road tunnel, has its unique properties, we adopt the technology of heat pipe and heat dissipation fins heat treatment in the form of hot channel vertical design, realize the modular heat, to keep the LED junction temperature under 70 ℃, ensure the LED long stable working under low light failure, improve the maintenance coefficient of lamps and lanterns, save maintenance cost.



     According to the flow characteristics of air in the tunnel, asymmetric ventilation design is carried out on the cooling cavity to ensure the convection of air cooling, and at the same time to reduce the automobile smoke and other pollutants into the cooling cavity, adsorption in the cooling structure leads to the reduction of cooling efficiency.



3.4 structural design



     The light weight of the lamp is less than 10kg. The protection level of LED light source cavity and electrical cavity shall be designed according to IP65, and the heat dissipation cavity shall be designed according to IP23. The light source cavity and heat dissipation cavity adopt reasonable isolation mode to avoid the mutual influence of heat flow between the light source cavity and heat dissipation cavity. Due to the lack of air circulation in the tunnel, automobile exhaust is doped with it, and the composition is complex. Therefore, LED tunnel lamps should have good corrosion resistance, exhaust gas, smoke and other chemical substances contained in the atmosphere inside the tunnel. The outer surface of each structural component should be treated with anti-corrosion treatment, making it meet the anti-corrosion requirements of GB/T7000.5.



     3.5 circuit design



     The positive volt-ampere characteristic of LED is similar to that of ordinary diode. Besides, if the positive voltage changes slightly, the positive current will change a lot, leading to the rapid increase of LED internal loss and heat, which will seriously affect the normal work and life of LED. To prevent this from happening, high-power leds must be powered by constant current. In order to maximize the efficiency of the current source and reduce heating, the input voltage of the current source must be reasonably controlled so that its maximum value, after deducting the internal voltage drop, is the same as the current and matches the total voltage required by the LED. Internal loss is small, the reliability of the current source can be guaranteed.



     Tunnel lighting generally needs a large number of lamps, huge power consumption, in order to save energy and reduce the "pollution" of the power grid, LED tunnel lamp driver also requires its power factor and harmonic generation must meet the relevant standard requirements, and appropriate consideration of electromagnetic interference and electromagnetic compatibility.



     (1) the switching power supply with high conversion efficiency and high stability, with the conversion efficiency over 87%, power factor over 95% and strong ability to resist voltage fluctuation of external power grid (96~264V), is equipped with constant current circuit design and drives LED light source in constant current mode to ensure the service life of LED.



     (2) adopt the control circuit suitable for tunnel lighting, so that the power of lamps and lanterns can be adjusted according to different lighting segments and time periods of the tunnel, so as to achieve good lighting effect and the purpose of energy saving. Different electric currents are used to drive the inlet section, the adaptive section, the transition section and the outlet section of the tunnel to make them as close as possible to the requirements of tunnel lighting curve and achieve the best lighting effect. The entrance and exit sections of the tunnel adopt timing regulation function, adjust the output current through PWM dimming or adopt double power supply, and at night use single power supply to reduce its power to 50% of daytime lighting, and effectively reduce the phenomenon of "bright hole" and "black hole" in both day and night.



     4. Conclusion



     The production, development, design and application of high-power tunnel lighting LED light source add extensive market for national railway and highway tunnel lighting, it not only fills the blank for the application of new tunnel light source in our country, but also makes a step forward on the road of low carbon, energy saving and environmental protection, which is worthy of comprehensive promotion and application.