Application of high power LED tunnel light analysis

In order to maintain the sustained and healthy development of the national economy, the country has in recent years increased investment in infrastructure construction, such as the construction of railways and highways. As a result, the demand for tunnel lighting equipment is increasing day by day. In order to save energy, protect the environment, improve the quality of tunnel lighting, and to adapt to the sustainable development of tunnel operation and management, combined with the special lighting environment and visual perception of the tunnel, it is necessary to find a reasonable new lighting theory and skill light source.

1. Comparison of the functions of conventional tunnel light and LED tunnel light

Currently, tunnel lighting uses high-pressure sodium lamps as light sources, but high-pressure sodium lamps have many deficiencies in terms of radiation form, color rendering, visual sensitivity characteristics, power specifications, brightness control, etc., and emerging LED tunnel lighting fixtures have excellent performance. In particular, the controllability of brightness overcomes many shortcomings of high-pressure sodium lamps and is becoming the mainstream lighting for tunnel lighting in the world today. The country has also introduced new measures for semiconductor lighting projects in the “Ten Cities”, bringing unprecedented opportunities for the development of LED tunnel lights.

LED (Light Emitting Diode) is a light emitting diode, which is a semiconductor light emitting technology. The earliest developed LED can only emit red light for the indicator light in electronic devices. With the development of technology, LED lights can now emit various colors of light, and are widely used in many types of industries. The main application markets include traditional display and signal lamp markets, backlight market, street lamps, tunnel lights, and automotive lighting markets. , outdoor landscape lighting and interior lighting market, special lighting market. LED as a tunnel light source has its unique advantages.

(1) The LED tunnel light consumes less power and saves energy. Compared with the traditional high-pressure sodium lamp, the energy consumption of the LED tunnel light saves more than 40%.

(2) The LED tunnel lamp has a long life, and in an ideal state it has 100,000 hours, while the lifetime of the high pressure sodium lamp and fluorescent tube is only 10,000 to 30,000 hours.

(3) The reliability of LED tunnel lights is high, daily maintenance and maintenance costs are low, MTBF is up to 20,000 hours, while MTBF of high-pressure sodium lamps and fluorescent tubes is less than 10,000. h.

(4) The construction cost of distribution systems (cables, transformers, distribution boxes, bridges, etc.) is reduced. For long-distance tunnels and long-distance power supply, the proportion of the cost of cables and distribution facilities is particularly large. LED tunnels are used. Lamps can greatly reduce the investment in cables and distribution equipment due to power saving.

(5) LED tunnel lights can achieve instant start, easy brightness adjustment, with no flicker, a wide range of starting voltage, etc., can achieve a variety of energy-saving methods, such as according to the traffic flow of roads, tunnels, intelligent adjustment of illumination and so on.

(6) High-pressure sodium lamps, fluorescent lamps, and electrodeless lamps contain chemical contaminants such as mercury and lead, while the LED tunnel lamp light source does not contain chemical pollutants and is a green and environmentally friendly light source.

2. Design requirements for high-power LED tunnel lights

(1) Basic lighting needs to be set in the tunnel either day or night. When the vehicle enters the tunnel during the daytime, the brightness of the road surface should gradually decrease, so that the driver's vision has an adaptation process. 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, which is usually determined according to the vehicle speed (V) with an adaptation time of T=2s, which can be estimated using S=VT/3.6m; the exit section should also be set to transition The lighting is the same as the entrance section in the two-way traffic situation.

(3) There shall be no enhanced lighting at night entrances and exits, and street lighting shall be provided outside the caves, the brightness shall not be less than 1/2 of the basic brightness in the cave; emergency lighting shall be provided in the tunnel, and its brightness shall not be less than 1/10 of the basic brightness.

(4) According to Chinese JTJ026-90 “Code for Design of Highway Tunnels”, the length of the tunnel entrance lighting zone and the minimum road brightness standard are designed as shown in Table 1.

3. Design scheme of high-power LED tunnel lights
3.1 LED light source selection LED single-watt lumen output is the basic indicator to determine whether the LED tunnel light has practical value, according to the requirements, the single-watt lumen LED of the LED tunnel light should reach 80 lumens, after nearly three years of LED light After the rapid development of efficiency, the LED luminous efficiency that can be supplied in large quantities at the present stage has reached more than 90 lm/W, and the brightness is still increasing. Table 2 provides the main technical parameters of the mass-produced high-power 1W white LED that represents the current top international manufacturers. OSRAM manufacturer LUWW5AM can be used as a design light source. Using LED light sources with a variety of different color temperatures to choose from, the LED light source with a color temperature similar to daylight of 4000~6000K can be selected to effectively 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 lighting segments. According to the optical principle and the high directivity of the LED light source, a reasonable light distribution is used to reduce the number of lamps and lanterns under the condition of satisfying the brightness or illumination requirements. The power to achieve energy savings.

(1) Asymmetrical illumination (backlight illumination) is applied to the inlet section, adaptation section, transition section, and exit section of the tunnel entrance section. Under the same illumination conditions, the brightness of the road surface can be increased by 121% compared to ordinary illumination. Using the advantage of high directionality, strict control of the light intensity in large angles, eliminating most of the glare.

(2) In the basic segment of the tunnel, the current distribution patterns of light distribution include concentrating light distribution, side-shooting light distribution, and lambertian light distribution. Different applications can be applied to different types of light distribution. For example, bat-wing light distribution for road lighting and concentrating light for spotlights should be used. Due to the particularity of tunnel lighting, the arrangement density of the lamps in the tunnel lighting is very high, so the secondary light distribution of the lamps in the tunnel lighting is different from the general road lighting. In the tunnel lighting, the bat airfoil light distribution and the Lambertian light distribution can all meet the requirements of illumination uniformity. This is mainly due to the relatively small lamp distance in tunnel lighting. Figure 1 shows the C0-direction light distribution diagrams of the two LED tunnel lights. The left side is the bat-airfoil light distribution used in road lighting and tunnel lighting, and the right side is the lambertian type light distribution. The use of batwing light distribution, that is, wide-band symmetric lighting distribution, can improve road surface brightness by 64% and increase road surface brightness evenness compared with ordinary illumination under the same illuminance conditions.

3.3 Heat Dissipation Design LED is an optoelectronic device. For the high-power LED currently in the forefront of the world, only 15%~20% of its electrical energy is converted into light energy in its working process. Most of the rest of the electrical energy is converted into heat energy, which makes the LED temperature. Increased. On the other hand, the lumen output of the LED decreases as the LED junction temperature increases, and the LED lifetime decreases as the junction temperature rises. Therefore, the good heat treatment of the LED will directly affect the use of the tunnel lighting effect and life.

At present, there are mainly three ways to dissipate heat from high-power LEDs: 1 Natural heat dissipation, forced fan cooling, and heat pipe plus heat sink fins. The natural heat dissipation utilizes natural convection and heat radiation, and the structure is reliable and easy to be waterproof, but the structural design of the lamp body itself is demanding. 2 Installing Fans Forced cooling mainly uses forced convection to achieve heat dissipation. The heat dissipation speed is fast, but the cost and noise are high, making it difficult to waterproof. 3 heat pipe plus cooling fins technology The main use of heat pipes to heat the LED heat conduction quickly to the cooling fins to achieve the purpose of heat dissipation, no moving parts, the system is stable, but the cost is relatively high.

Due to the unique nature of tunnels compared to ordinary roads, we use heat pipes and cooling fins for thermal treatment. The vertical design of the thermal channels enables modular heat dissipation and keeps the LED junction temperature below 70°C. LED work under low light and stable for a long time, improve the maintenance factor of the lamp, save the maintenance cost.

According to the flow characteristics of the air flow in the tunnel, the asymmetrical ventilation design of the heat dissipation chamber ensures the convection of the air and heat dissipation. At the same time, the fumes and other pollutants generated by the automobile are reduced to enter the heat dissipation chamber. Adsorption on the heat dissipation structure results in reduced heat dissipation efficiency.

3.4 Structural Design Lightweight aluminum alloy housing is used. The weight of the lamps is less than 10kg. The LED light source cavity and electrical cavity protection class are designed according to IP65, and the cooling cavity is designed according to IP23; the light source cavity and the cooling cavity adopt a reasonable isolation mode to avoid the influence of the heat flow of the light source cavity and the cooling cavity. Because the air in the tunnel does not circulate, the vehicle exhaust gas is doped and the components are complex. Therefore, the LED tunnel luminaire should have good corrosion resistance, exhaust gas, smoke, and other chemical substances contained in the atmosphere in the tunnel, and the outer surfaces of the various structural components should be protected against corrosion. Treat it to meet the corrosion protection requirements of GB/T7000.5.

3.5 Circuit Design The positive volt-ampere characteristic of the LED is similar to that of an ordinary diode. The forward voltage is slightly changed. The forward current will greatly change, causing the LED internal loss and heat to rise rapidly, which will seriously affect the normal operation and life of the LED. . To prevent this from happening, high-power LEDs must generally be powered in a constant current mode. 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, after deducting the internal voltage drop, is the same as the current and also matches the total voltage required by the LED. The internal loss is small, and the reliability of the current source can be guaranteed.

Tunnel lighting generally requires a large number of lamps, and the power consumption is huge. In order to save energy and reduce the "pollution" of the grid, the driver of the LED tunnel lamp also requires that its power factor and generated harmonics must meet relevant standards, and electromagnetic considerations should be taken into consideration. Disturbance and electromagnetic compatibility.

(1) Using high conversion efficiency, high stability power supply, conversion efficiency greater than 87%, power factor greater than 95%, and switching power supply (96~264V) resistant to external power grid voltage fluctuation, together with constant current circuit design The constant current mode drives the LED light source to ensure the service life of the LED.

(2) The control circuit suitable for tunnel lighting is used to adjust the power of the lamps according to different illumination sections and different time periods of the tunnel to achieve good lighting effects and energy saving. The introduction section, adaptation section, transition section and exit section of the tunnel entrance section are driven with different currents to make it as close to the tunnel lighting curve as possible to achieve the best lighting effect; the timing adjustment function is applied to the tunnel entrance section and exit section. The PWM dimming regulates the output current or uses dual power supply. At night, it is powered by a single power supply, reducing its power to 50% of daytime lighting. Both day and night, both the "light hole" and the "black hole" are effectively reduced. "phenomenon.

4. Conclusion

The production and development of high-power tunnel lighting LED light sources, design and application, has added a wide-spread market for the national railway and highway tunnel lighting. It not only fills a gap for the application of new tunnel light source in China, but also makes progress on the road of low-carbon energy conservation and environmental protection. The step is worthy of comprehensive promotion and application.