Application of LED in traffic lights

Source: Queendom Technology Co., Ltd. Author: JACKY Date: 22 May 2020

Because LED has the advantages of high brightness, power saving and long life, it has been widely used in traffic signal lights. According to statistics, there are about 20 million traffic lights in the world. In 2000, there were about 400,000 Pingtian LED traffic lights in the world. In 2001, it reached 1 million, with a growth rate of 150%. If you consider the new traffic lights installed each year and the replacement of old ones It is estimated that 2 million LED traffic lights will be added globally every year. Based on the cost of each replacement of about 500 US dollars, in the future, there will be a 1 billion US dollar market for LED traffic signal consumption in urban LED traffic lights.

At night, high-luminance LED urban traffic lights have also begun to be applied. Shanghai has clearly stipulated that Anjing’s traffic signals use LEDs. Each intersection in Yincheng City requires 12 yellow and green lights (4), plus 24 (8 sets) of crosswalk warning lights. Of 36, 12 of them are blue and green signal lights, so each intersection needs 2400 bright blue and green LEDs. In 2000, there were 663 cities nationwide, including 37 megacities and 51 large cities, including 216 Zhongbo cities, There are 359 small cities. Based on an average of 500 intersections in each city, the national unity needs about 800 million high-brightness blue and green LEDs.

With the expansion of cities and the acceleration of urbanization, municipal construction facilities are also a large space. Small cities and even towns need to be equipped, including highway entrances and exits, and traffic lights at highway intersections. It is estimated that this is a market of more than 1.5 billion yuan. As the requirements for energy conservation, environmental protection and traffic safety continue to increase, and the price of LEDs continues to fall, the use of LEDs to replace old lights and traffic signal lights is bound to increase. .

Device Design of LED Traffic Signal Light

Using LED traffic lights to replace traditional incandescent lamps can save electricity by more than 80%, and its optical properties are better than using 100W incandescent lamps. In order to ensure that the service life of traffic lights can exceed 5 years, the following technical measures should be taken when designing LED traffic lights.

. Use LED chips with higher brightness. It is best to use a copper bracket for the selected LED. When designing a printed circuit board, the area of the copper clad board should be reserved, which is conducive to the heat dissipation of the LED (the heat is dissipated by the copper strip of the circuit board).

When selecting LED, its design index should be 20% brighter than that required by traffic signal lights. The use of reflector technology can improve the light output effect of signal lights.

 The driving current should be a reliable constant current power supply. When the voltage changes within ±20%, the current change is controlled within ±1 mA. Since the forward voltage of the LED decreases with the rising surface of the temperature, if the resistance step-down, capacitor step-down or constant voltage method is adopted, the current will increase and the temperature will rise, which will cause a vicious cycle until the LED is damaged.

The current that each LED bears should leave room, which is less than the current value of 20mA normally used at room temperature. For example, red and yellow LEDs use 17~18 mA, and blue and green LEDs use about mA. From the limit of LED operating current and ambient temperature The relationship can be seen that for the red and yellow LEDs, when the temperature rises to 80C, the limiting current is only 23, and when the temperature rises to 70C, the limiting current is only 10 mA, which exceeds the allowable current limit of the two LEDs. The LED will be damaged.

Technical standards for LED traffic lights

So far, LED traffic lights have circular red, green, and yellow lights, arrow-like green lights, and sidewalk red, yellow, and green lights. The technical standards of these types of lamps are different, but their light intensity and brightness values are measured with a horizontal overhead angle. On a horizontal bare ground, there are 5" on both sides of the horizontal angle, 10° on both sides of the horizontal angle, 15" on both sides of the horizontal angle, 20" on both sides of the horizontal angle, 30" on both sides of the horizontal angle, etc.: and the top and bottom are the depression angles on the optical axis 5°, depression angle of 10", depression angle of 20* to measure the optical indicators of the famous spot. The color of the signal light is different in different countries.

Due to the harsh environmental conditions of traffic lights, high and low temperature tests should be performed on them in cycles at -40~60C. The requirements for the waterproof conditions of the traffic signal lights are also relatively high. Under a certain water pressure, the traffic signal lights can be impacted from all aspects, and it is necessary to ensure that no water enters. Dustproof is also another requirement for traffic lights, that is, the surface lens must not be dusty. For the above standards, you can check the specific test indicators of the transportation department. There is a research institute in the transportation department that is responsible for the test and inspection of traffic signal indicators.

At present, the LEDs used in traffic lights are different. There are a combination of 05 mm red, green and yellow single tubes. Because a single LED emits a small luminous flux, 100-300 LEDs are usually used to make them evenly distributed on the entire light-emitting surface. on. With the improvement of the light-emitting efficiency of a single LED, only Shierdun LEDs can be used to form a signal light.

As for the LED as a traffic signal light, it should be designed according to the relevant technical index requirements and the basic parameters of a single LEDE voltage, current, luminous flux, etc. Now there are many technical information for designing traffic signal lights for reference by relevant professional and technical personnel.

Source: Queendom Technology Co., Ltd. Author: JACKY date: 2020 May 22 http://www.cn-led.net

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Source: Queendom Technology Co., Ltd. Author: JACKY date: 2020 May 22 http://www.cn-led.net/en