introduction
In recent years, in order to maintain the sustained and healthy development of the national economy, the state has increased investment in infrastructure construction, such as the construction of railways and highways. The demand for such tunnel lights is increasing. In order to save energy, protect the environment, improve the quality of tunnel lighting, and in order to adapt to the sustainable development of tunnel operation management, it is necessary to find a reasonable new lighting theory and skill light source in combination with the special lighting environment and visual perception of the tunnel.
1 Comparison of the functions of conventional tunnel lights and LED tunnel lights
At present, most of the tunnel lighting uses high-pressure sodium lamps as the light source, but the high-pressure sodium lamps have many shortcomings in terms of radiation form, color rendering, visual sensitivity, power specifications, brightness control, etc., and the emerging LED tunnel lighting fixtures have excellent performance. In particular, the controllability of brightness overcomes many of the shortcomings of high-pressure sodium lamps and is becoming the mainstream of tunnel lighting in the world today. The state has also introduced new measures for the “Ten Cities and Ten Thousand Cities†semiconductor lighting project, which has brought unprecedented opportunities for the development of LED tunnel lights.
LED (Light Emitting Diode) is a semiconductor light emitting technology. The earliest developed LEDs only emit red light for the indicator lights in electronic devices. With the development of technology, LED lamps have been able to emit various colors of light and are widely used in many industries. The main application markets include the traditional display and signal market, backlight market, street lamps, tunnel lights, and automotive lighting markets. , outdoor landscape lighting and interior lighting market, special lighting market. LEDs have their unique advantages as a tunnel light source.
(1) LED tunnel light has low power consumption and energy saving, and its energy consumption is more than 40% compared with traditional high-pressure sodium lamps.
(2) LED tunnel lights have a long life, ideally 100,000 h, while high-pressure sodium lamps and fluorescent tubes have a lifetime of only 10,000 to 30,000 h.
(3) LED tunnel lights have high reliability, low daily maintenance and repair costs, mean time between failures (MTBF) of up to 20,000 h, and low mean time (MTBF) of high pressure sodium and fluorescent tubes of less than 10,000 h.
(4) Reduce the construction cost of power distribution systems (cables, transformers, distribution boxes, bridges, etc.). For long tunnels and long-distance power supply, the proportion of cables and distribution facilities is particularly large. LED tunnels are used. Lights can greatly reduce investment in cables and power distribution equipment due to power saving.
(5) LED tunnel light can realize instant start, easy to adjust brightness, has no stroboscopic, wide starting voltage range, etc. It can realize various energy-saving modes, such as intelligent adjustment of illumination according to road and tunnel traffic.
(6) High-pressure sodium lamps, fluorescent lamps, and electrodeless lamps contain chemical pollutants such as mercury and lead, and the LED tunnel light source does not contain chemical pollutants, and is a green light source.
2 Design requirements for high power LED tunnel lights
(1) Basic lighting is required in the tunnel whether it is day or night. When the vehicle enters the tunnel during the day, the road surface brightness should be gradually reduced, so that the driver's vision has an adaptation process, and the entrance section is divided into an introduction section, an adaptation section and a transition section.
(2) Determine the length (S) of the lead-in section, the adaptation section and the transition section. Usually, the vehicle speed (V) is determined by the adaptation time of T=2s, which can be estimated by S=VT/3.6m; the exit section should also be set to transition. Illumination, in the case of two-way traffic, the same as the entrance section.
(3) There is no reinforced lighting at night entrances and exits, and street lights should be set outside the caves. The brightness should not be less than 1/2 of the basic brightness in the cave; emergency lighting should be provided in the tunnel, and its brightness should be no less than 1/10 of the basic brightness.
(4) According to the provisions of JTJ 026-90 “Code for Design of Highway Tunnelsâ€, the length of the tunnel entrance lighting interval and the minimum brightness standard of the road surface shall be designed as required in Table 1.
3 high power LED tunnel light design
3.1 LED light source selection
The LED single-watt lumen output is the basic indicator for determining whether the LED tunnel light has practical value. According to the requirements, the single-watt lumen of the LED used for the LED tunnel light should reach 80 lumens or more. After nearly three years of high-speed development of LED luminous efficiency. At present, the LED light effect that can be supplied in large quantities has reached 90 lm/W or more, and the brightness is continuously increasing. Table 2 provides the main technical parameters of the high-volume 1W white LEDs that are produced by several of the world's most advanced manufacturers. The OSRAM manufacturer LUWW5AM can be used as the design light source. The LED light source can be selected from a variety of different color temperatures. The LED light source with a color temperature of 4000~6000K can be effectively reduced to reduce the "light hole" and "black hole" effects.
3.2 Light distribution design
According to the tunnel lighting requirements, different light distribution lamps are used according to different illumination sections. According to the optical principle and the high directivity of the LED light source, a reasonable light distribution is adopted, and the power of the lamps is reduced to meet the brightness or illumination requirements. The purpose of energy saving.
(1) The introduction section, the adaptation section, the transition section and the exit section of the tunnel entrance section adopt asymmetric lighting (backlighting), which can improve the road surface brightness by 121% under the same illumination conditions. The advantage of high directivity is utilized, and the light intensity in a large angle direction is strictly controlled to eliminate most glare.
(2) In the basic section of the tunnel, the current common distribution patterns of light distribution include concentrating light distribution, side-emitting light distribution, and Lambertian light distribution. Different application modes are applicable to different light distribution forms. For example, Road Lighting should use batwing type light distribution, and spot light should adopt concentrating 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 the lamps in tunnel lighting is different from general road lighting. In the tunnel illumination, the batwing type light distribution and the Lambertian type light distribution can meet the requirements of illumination uniformity, which is mainly due to the relatively small lamp distance in the tunnel illumination. Figure 1 shows the C0 direction light distribution of the two LED tunnel lights. The left side is the commonly used batwing light distribution in road lighting and tunnel lighting, and the Lambertian light distribution on the right. The batwing light distribution, that is, the wide-band symmetrical illumination light distribution, can improve the road surface brightness by 64% and improve the road surface brightness uniformity under the same illuminance condition.
3.3 Thermal design
LED is a photoelectric device. In the current high-power LEDs at the forefront of the world, only 15%~20% of the electrical energy is converted into light energy during the working process, and most of the remaining electrical energy is converted into thermal energy, which causes the temperature of the LED to rise. On the other hand, the lumen output of the LED decreases as the junction temperature of the LED increases, and the lifetime of the LED decreases as the junction temperature increases. Therefore, the heat dissipation treatment of the LED is directly related to the use effect and life of the tunnel luminaire.
At present, there are three main ways to dissipate heat from high-power LEDs: 1 natural heat dissipation, forced cooling of the fan, and heat pipe and fin technology. The natural heat dissipation utilizes natural convection and heat radiation, has a reliable structure, and is easy to be waterproof, but has high requirements on the structural design of the lamp body itself. 2 Adding a fan to force heat dissipation mainly uses forced convection to achieve heat dissipation, and the heat dissipation speed is fast, but the cost and noise are high, and it is difficult to waterproof. 3 Heat pipe and heat sink fin technology mainly uses heat pipes to quickly transfer the heat generated by LEDs to the heat sink fins to achieve heat dissipation. There is no moving parts, the system is stable, but the cost is relatively high.
Because the tunnel has its unique properties compared with the general road, we use the heat pipe and heat sink fin technology to dissipate heat, and the hot channel vertical design realizes the modular heat dissipation, so that the LED junction temperature is kept below 70 °C, ensuring LEDs work stably for a long time with low light decay, improve the maintenance factor of the lamps and save maintenance costs.
According to the flow characteristics of the airflow in the tunnel, the asymmetric ventilation design of the heat dissipation cavity ensures air convection heat dissipation, and at the same time, the dirt generated by the automobile and the like are reduced into the heat dissipation cavity, and the heat dissipation structure is reduced by the heat dissipation structure.
3.4 Structural design
Lightweight Aluminum Alloy casing, the weight of the lamp is less than 10kg. The LED light source cavity and the electrical cavity protection grade are designed according to IP65, and the heat dissipation cavity is designed according to IP23; the light source cavity and the heat dissipation cavity are properly isolated to avoid the mutual influence of the heat flow between the light source cavity and the heat dissipation cavity. Since the air in the tunnel is not circulated, the exhaust of the automobile is doped and the composition is complicated. Therefore, the LED tunnel luminaire should have good corrosion resistance, exhaust gas, smoke and other chemicals contained in the atmosphere of the tunnel. The outer surfaces of each structural component are protected against corrosion. Processed to meet the corrosion protection requirements of GB/T7000.5.
3.5 Circuit Design
The forward volt-ampere characteristics of LEDs are similar to those of ordinary diodes. The forward voltage is slightly changed, and the forward current will change greatly, causing the internal loss and heating of the LED to rise rapidly, which seriously affects the normal operation and life of the LED. In order to prevent this from happening, high-power LEDs must generally be powered by constant current. In order to maximize the efficiency of the current source and reduce heat generation, the input voltage of the current source must be reasonably controlled so that its maximum value is the same as the current after deducting the internal voltage drop, and also matches the total voltage required by the LED. The internal losses are small and the reliability of the current source is guaranteed.
Tunnel lighting generally requires a large number of lamps, and the power consumption is huge. In order to save energy and reduce the "contamination" of the power grid, the driver of the LED Tunnel Lamp also requires that its power factor and harmonics must meet the relevant standard requirements, and properly consider the electromagnetic Interference and electromagnetic compatibility.
(1) Adopting a power supply with high conversion efficiency and high stability, the conversion efficiency is greater than 87%, the power factor is greater than 95%, and the switching power supply (96~264V) with strong resistance to external grid voltage fluctuation is matched with constant current circuit design. The constant current mode drives the LED light source to ensure the service life of the LED.
(2) Adopting the control circuit suitable for tunnel illumination, the lamps can be adjusted according to different illumination segments and different time periods of the tunnel to achieve good lighting effect and energy saving. The introduction section, the adaptation section, the transition section and the exit section of the tunnel inlet section are driven by different currents so as to be as close as possible to the tunnel lighting curve requirements to achieve the best lighting effect; the timing adjustment function is adopted for the tunnel inlet section and the exit section. The PWM output is regulated by PWM dimming or dual-supply operation. At night, it is powered by a single power supply, reducing its power to 50% of daylight illumination, effectively reducing “light holes†and black holes in day and night. phenomenon.
4 Conclusion
The development, design and application of high-power tunnel lighting LED light source has added a wide market to national railway and highway tunnel lighting. It not only fills the gap for the application of new light source in tunnels in China, but also advances on the road of low-carbon energy-saving and environmental protection. One step is worth promoting the application.
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