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With the global industrial development, the industrialization process in a significant increase in carbon dioxide emissions, global climate deterioration, flooding parts of drought, hail, snow record when the potential serious threat to human survival. A common response to threat, in December 2009, world leaders gathered in Copenhagen to discuss energy conservation plans, local plans to actively develop and implement low-carbon. As a green, environmentally friendly energy saving LED lighting, more and more popular by the countries, China’s “Ten City, ten thousand,” Los Angeles “one hundred and forty thousand Plan” is in full swing implementation.The dimming LED lighting technology in the successful application will further enhance the energy saving effect.

Power as a green energy, energy applications in the field of national accounts for an increasing proportion. According to the China Academy of Engineering, Liang-Hui Chen survey concluded, estimated in 2010, the country’s electricity consumption will reach 2.7 trillion kWh, of which lighting power consumption will be over 300 billion degrees. LED lighting power consumption by traditional incandescent and HID lamps only 1 / 3 that the use of LED lights to replace the existing traditional lamps, is expected to save power 2 / 3. The effect of energy conservation is evident.

Dimming technology will further reduce energy consumption and save electricity for lighting. Currently, public lighting electricity consumption accounted for one third of the lighting field, up to 1,000 billion kWh. In China, the city generally from 5:30 or 6:00 the evening light, small cities, however, after 9 o’clock at night, 12 major cities after midnight, the road on the road were rare, even in Beijing, Shanghai and Guangzhou, the bustling city, am 2,3 point, the path of pedestrians and vehicles are rare. From this time until 6 am lights off, in light traffic on the road remained high illumination apparently not very necessary. If using dimming technology enables the output power LED street light 12 after midnight with a decrease in traffic flow reduced to half, will save electricity up to 500 billion kWh, equivalent to saving the 2009 annual power generation of Three Gorges Power Station about five eighths (of the Three Gorges power station generating 79.85 billion kwh in 2009), energy-saving effect is very significant.

Dimming technology used to reduce the output power, LED lamps will significantly improve the working environment, extended lamp life and improve reliability. The reliability of LED lighting key factor is temperature. Whether or LED chip LED drive power, the higher the ambient temperature, its life and reliability will be a sharp decline. Figure of a lifetime for the LED drive power relationship with temperature when the ambient temperature is 25 ℃, the power LED life of up to 320,000 hours, and when the temperature rose to 60 ℃,, LED power supply of the life will be shortened to only 35,000 hours.

The higher the temperature, LED chips, light failure was significantly increased.Figure II for the Cree’s LED light source decay curve. It can be seen from the figure, LED light failure and its junction temperature is closely related to the so-called PN junction semiconductor junction temperature is the temperature, the higher the junction temperature, LED light source light failure occurs sooner, that is, the shorter life expectancy. It can be seen from the chart, if the junction temperature of 105 ℃, the brightness to 70% of the LED light source life span of only more than ten thousand hours; junction temperature of 95 ℃ when the LED light source life span 20,000 hours; and junction temperature down to 75 ℃ life can be long to reach 5 million hours, 65 ℃ when the life expectancy may be extended to 90,000 hours. In summary, the key to extend the life of LED light source is to reduce the junction temperature.

Figure II Cree’s LED light decay curve

By dimming technology, with the reduced output power, drive power consumption will also lower its own, the shell temperature will also be reduced. As shown in Fig 200W LED driver power supply output power and the Shell shell temperature curve.When the ambient temperature is 25 ℃ full load, case temperature is 50 ℃, and the use of dimming controls only 50% of output power, the case temperature dropped to 40 ℃, life expectancy will double, reliability can be increased by 25% - 40%.

Figure III LED driver power supply output power and the Shell shell temperature curve

Unable to traditional incandescent or HID dimming, the energy crisis of the seventies in Japan, has tried to use the interval method of energy saving lighting.However, due to uneven illumination of the road, causing problems with vision of pedestrians, public order and road traffic accidents increased sharply, and finally had to give up interval lighting method. Dimming technology, the rapid development of LED lighting, dimming system will bring a new field, thus saving green LED lighting applications for a wide range of popular and promotion.

Second, LED lamps dimming technology mainly Introduction

First began to be used in LED lighting and other public roads, in the promotion of early, some LED lamp factory in order to achieve the purpose of energy saving, borrowed the idea of lighting the interval will be an LED light LED chip is divided into two parts, control their drive current on and off, before 12 o’clock midnight, all the LED lights up fully, disconnect the half after 12 o’clock, in order to save energy. Such dimming energy saving can achieve a certain effect, the uniformity of illumination than the traditional way of lighting a significant improvement in the interval, but the impact of LED lamps will light distribution curve. To further improve the efficiency and LED lamps light distribution curve, and some LED lights LED chip factory and consider the arrangement with the interval mode, only seen in the dimming light interval or off, to a certain extent, improved the uniformity and with light.

Brightness LED chips and LED drive current into a proportional set, so by adjusting the LED drive current to achieve the LED lights dimming, dimming the second way is often called analog dimming mode or linear dimming. This kind of approach has the advantage of dimming: When the drive current linear increase or decrease, the relative reduction of the drive current to the LED chip in overshoot the impact of a strong anti-interference control circuits. The disadvantage is the size of the drive current changes the color temperature of the chip LED will have a certain influence.Such a typical dimming applications are currently six potential Anhui, six armed highway LED tunnel lighting.

The third way is dimming light pulse modulation (PWM) mode. Some of the ways is through the control of the drive current was square wave, the pulse width variable pulse width adjustment by changing the LED lights continue to light up the time, and also changes the power output to achieve energy saving. Frequency control in general 200Hz ~ 10KHz, because the human eye visual retention, will not feel the light in the dimming occurred during the flashing. This approach has the advantage of dimming LED cooling can improve the disadvantage of drive current overshoot the life of the LED chip to a certain extent.

These three methods are dimming LED drive current based on output control to the classification. Analog control circuit can be divided into control and PWM control, the control circuit is usually through the micro-controller (such as SCM) to achieve.

Third, the composition of the dimming system and future development

Sound should have manual control intelligent control, intelligent control, light control, time control and fault alarm control functions. When the sun goes down darkening the sky light up automatically after midnight after the light illumination 12 can be automatically reduced by half; dawn, the lamp automatically turns off; special circumstances, one can manually control; failure in the lighting control system can automatically alarm.

Intelligent Light system consists of server, central controller, single-chip controller and signal detection circuit four major components, as shown in Figure IV.

Figure Four intelligent light control system

Server: the host computer and PC software components, the main achievement monitoring operation and alarm functions. Street management server is the control center, and its links with the central controller can be used between the power line, network or wireless means.

Central Controller: responsible for receiving the signal sent by the server and decoded and sent to the unit controller, to achieve control, while the results of signal detection to send to the server.

Signal detection circuit: detecting environmental brightness, power supply voltage and current. And detecting a signal sent to the unit from the controller or central controller.

Cell controller: Each LED lamp has a lamp unit controller, through the central controller receives the command, or the dimming of the LED on and off control, LED lights while driving voltage and current delivered through the signal detection circuitcentral controller. When the LED lamp failure fault signals will be transmitted to the central controller.

Currently in the field of road lighting, LED applications are rapidly growing popularity, long life and reliability is still the first factor to consider, but with the technology, life and reliability problems when a certain extent have been solved, LEDApplication of intelligent lighting dimming system inevitably toward a big step forward.