With the development of global industry, the carbon dioxide emissions in the process of industrialization have increased greatly, the global climate has deteriorated, and there have been record-breaking trends in floods and hailstorms in various places, which seriously threaten the survival of mankind. In order to jointly respond to threats, in December 2009, heads of state gathered in Copenhagen to discuss energy conservation and emission reduction plans, and local governments actively formulated and implemented low-carbon plans. As a green, environmentally-friendly and energy-saving LED lighting, it is increasingly favored by all countries. China's “Ten Cities and Ten Thousand Cities” and the “140,000 盏 Plan” in Los Angeles are in full swing. The successful application of dimming technology in LED lighting will further enhance the effect of energy saving and emission reduction.
First, the necessity of dimming
As a kind of green energy, electric energy accounts for a growing proportion of energy applications in various countries. According to a survey conducted by Chen Lianghui, an academician of the Chinese Academy of Engineering, it is estimated that in 2010, the country's electricity consumption will reach 2.7 trillion kWh, of which lighting power consumption will exceed 300 billion kWh. Because LED lighting consumes only 1/3 of traditional incandescent lamps and HID lamps, it would be possible to save 2/3 of the energy if LED lamps are used to replace existing conventional lamps. Its energy-saving effect can be seen.
The application of dimming technology will further reduce energy consumption and save electricity for lighting. At present, public lighting electricity accounts for one-third of the entire lighting field, up to 100 billion degrees. In China, cities generally start to light from 5:30 or 6:00 in the evening. However, after 9:00 in the small city and after midnight in the big and medium-sized cities, there are few passers-by on the road, even in Beijing, Shanghai and Guangzhou. In the city, after 2 or 3 in the morning, pedestrians and vehicles are rare on the road. From this period of time to 6 o'clock in the morning, the street lights are extinguished, and it is obviously not necessary to maintain a high illumination on the road with low traffic flow. If dimming technology can be adopted, the output power of LED street lamps will be reduced to half with the decrease of traffic flow after 12 o'clock in the middle of the night, which will save up to 50 billion kWh of electricity, which is equivalent to saving the annual power generation of the Three Gorges Power Station in 2009. About five-fifths (the Three Gorges Power Station generated 79.85 billion kWh in 2009), the energy-saving effect is very significant.
The use of dimming technology to reduce the output power will significantly improve the working environment of LED lamps, extend the life of lamps and improve reliability. The key factor affecting the reliability of LED luminaires is temperature. Whether it is an LED driver or an LED chip, the higher the ambient temperature, the sharper the life and reliability. Figure 1 shows the relationship between LED driver power life and temperature. When the ambient temperature is 25 °C, the LED power supply life is up to 320,000 hours, and when the temperature rises to 60 °C, the life of the LED power supply will be shortened to only 35,000 hours.
LED drive power life and temperature curve
The higher the temperature, the more pronounced the light decay of the LED chip. Figure 2 shows Cree's LED light source light decay curve. It can be seen from the figure that the light decay of the LED is closely related to its junction temperature. The so-called junction temperature is the temperature of the semiconductor PN junction. The higher the junction temperature, the earlier the LED light source has a light decay, that is, the shorter the lifetime. As can be seen from the figure, if the junction temperature is 105 ° C, the LED light source whose brightness is reduced to 70% has a lifetime of only over 10,000 hours; when the junction temperature is 95 ° C, the life of the LED light source is 20,000 hours; and the junction temperature is reduced to 75 ° C. The life expectancy can be as long as 50,000 hours, and the life expectancy can be extended to 90,000 hours at 65 °C. In summary, the key to extending the life of LED light sources is to reduce the junction temperature.
Cree's LED light decay curve
With dimming technology, as the output power is reduced, the loss of the drive power supply will also decrease, and the case temperature will also decrease. As shown in Figure 3, the 200W LED drive power output power and the case temperature curve. When the ambient temperature is 25 ° C full load output, the case temperature is 50 ° C, and when the dimming technology is used to control the output only 50% power, the case temperature drops to 40 ° C, the life will also double, the reliability can be increased by 25% - 40%.