1 LED development history
LED has developed to nearly 40 years of history. The first commercial LEDs appeared in 1968. Although LEDs have been limited by color and luminous efficiency for many years, GaP and GaAsPLEDs have long life, high reliability, low operating current, and TTL, CMOS digital circuits. With many advantages, such as compatibility, it has been popular among users, and has begun to enter a variety of applications including aerospace, aircraft, automotive, industrial applications, communications, etc. By 1996, LED sales worldwide had reached billions of dollars.
In the past decade, the forefront of research on LED materials and device technology has been ultra-high brightness and full color. The so-called ultra-high brightness LED (UHB) refers to LEDs with luminous intensity up to or exceeding 100mcd, also known as candela (cd) level LEDs. Due to the use of A1GaInP and InGaN as the light-emitting layer, the development of ultra-high-brightness LEDs is progressing rapidly and reaches the performance level that conventional materials GaA1As, GaAsP, and GaP cannot achieve. In 1991, Toshiba Corporation of Japan and HP Corporation of the United States developed InGaA1P (λ=620nm) orange ultra-high brightness LED. In 1992, InGaA1p (λ=590nm) yellow ultra-high brightness LED was put into practical use. In the same year, Toshiba developed InGaA1P (λ = 573nm) yellow-green ultra-high brightness LED, the normal light intensity reached 2cd. In 1994, Japan Nichia Corporation developed an InGaN (λ=450nm) blue (green) color ultra-high brightness LED.
At this point, the three primary colors of red, green, blue, and orange and yellow LEDs required for color display have reached the candela-level luminous intensity, achieving ultra-high brightness and full color, and making the outdoor full color of the luminous tube. The display becomes a reality.
Through technological transformation, technological breakthroughs, the introduction of foreign advanced equipment and some key technologies, China's LED production technology has taken a step forward. Taiwan is the world's leading producer of LEDs and dies. With an annual output of about 4 billion LEDs, the product specifications are complete, the performance is close to the world's advanced level, and the produced dies are also exported to Japan and other countries.
2 Basic performance of ultra-high brightness LED
2.1 Basic characteristics of various colors of ultra-high brightness LED
The ultra-high-brightness red A1GaAs LED has higher luminous efficiency, and the lumen efficiency of the transparent substrate (TS) A1GaAs LED (640 nm) is close to 10 lm/w, which is 10 times larger than that of the red GaAsP-GaPLED. Ultra-high brightness InGaAlPLED provides the same color as GaAsP-GaPLED, including: green yellow (560nm), light green yellow (570nm), yellow (585nm), light yellow (590nm), orange (605nm), light red (625nm), deep Red (640nm). The InGaAlPLED absorber substrate (AS) has a lumen efficiency of 101m/w, a transparent substrate (TS) of 201m/w, and a lumen efficiency of 10-20 times higher than the GaAsP-GaPLED in the wavelength range of 590-626nm; The -570 wavelength range is 2-4 times higher than GaAsP-GaPLED. Ultra-high-brightness InGaN LEDs provide blue and green light with a wavelength range of 450-480 nm for blue, 500 nm for blue and 520 nm for green, and a lumen efficiency of 3-151 m/w.
2.2 Comparison of ultra-high brightness LEDs and incandescent lamps
At present, the lumen efficiency of ultra-high-brightness LEDs has exceeded that of incandescent lamps with filters. Some varieties have higher brightness than 1000mcd, which can replace incandescent lamps with a power of less than 1W. The array of LEDs can even replace the power within 150W. Incandescent lamp. For many urban lighting system applications, incandescent lamps use filters to get red, orange, green, and blue, while ultra-high brightness LEDs give the same color directly. In recent years, ultra-high brightness LEDs made of AlGaInP materials and InGaN materials have combined multiple (red, blue, green) ultra-high brightness LED chips, which can be red, orange, yellow, green and blue without filters. The seven colors inside, the luminous efficiency of which has now exceeded the incandescent lamp, and the positive fluorescent lamp is close. In addition, a large color screen composed of ultra-high-brightness LEDs can express the sky and the ocean for 3D animation.
A new generation of red, green and blue ultra-high brightness LEDs has achieved unprecedented performance. Recently, Nichia Corporation of Japan used its InGaN blue LED and fluorescent technology to introduce a new white light-emitting device with a color temperature of 6500K and an efficiency of 7.5 lumens per watt. The advent of ultra-high-brightness LEDs and their industrialization have added new vitality to solar lighting systems.
3 Ultra-high brightness LED application in solar city lighting system
3.1 The basic structure of ultra-high brightness LED bulb
Applied to the solar city lighting system, the single ultra-high-brightness LED light-emitting tube produces light that is dark, directional, and has a poor overall visual effect. Therefore, when applied to a solar city lighting system, firstly, a plurality of LED light-emitting tubes must be concentrated together to increase the brightness and area of ​​the light-emitting; secondly, according to the difference in performance of different color LED tubes, the relevant parameters are matched to optimize the design and combination. For DC 12V, 6V, 4.8V and other pulse series products, the main technical parameters of typical DC LED high-efficiency energy-saving bulbs are shown in Table 1.
Finally, according to the requirements of the place of use, the reflectors of 120°, 90° and 70° angles are designed and placed in a high-transmission plastic lampshade (Fig. 1) to improve the directivity of the LED. The spot is also designed with a grid-shaped refractive surface on the inner surface of the lampshade, so that the light emitted by the LED is reflected and refracted multiple times, and finally the LED high-efficiency energy-saving bulb is uniformly illuminated and forms a special optical effect.
3.2 Application examples
At present, the solar city lighting system using the LED high-efficiency energy-saving light bulb mentioned above has established demonstration projects in Wuhan, Shenzhen, Beijing and other places, and is now widely used in Hubei, Hubei, Ezhou, Henan Xinyang, Liaoning Dalian, Jiangxi Pingxiang and other places. Application has been recognized by society and consumers.
Take the Liangjiang four-shore lighting project in Wuhan as an example. The project construction site is located along the Yangtze River and Hanshui River in Wuhan. It belongs to one of the key lighting areas in Wuhan. It requires the lighting system to be clean, environmentally friendly, safe, energy-saving, durable, and reliable. Flexible use, high performance and price ratio.
Therefore, the system uses 1500 ç› LED high-efficiency energy-saving light bulbs to outline the exterior of the building. Because the system controller has a rich color light control mode control program, the automatic control light uses a variety of changes such as monochrome, multi-color, flash, chasing, beating, shining, etc., fully demonstrating the strong dynamic and smooth vision of the solar LED lighting system. effect. At the same time, it is estimated that the system has a power saving rate of more than 85% compared with the ordinary lighting system, and the annual electricity consumption cost is only 500 yuan. After many of the lighting projects in China are completed, often due to insufficient electricity costs, the lighting spots cannot be fully illuminated. Or can not be bright for a long time, thus affecting the practical effect of urban lighting.
In addition, as the demonstration city of renewable energy application in China, the relevant departments of the municipal government have decided to apply or transform the lighting project of 56 parks in more than 70 parks in the city into solar city lighting systems.
3.3 The practical and commercial significance of ultra-high brightness LED in solar lighting system
The practical and commercialization of ultra-high-brightness LEDs in solar lighting systems has brought a new revolution in urban lighting technology. Although the cost of this new type of bulb made of many ultra-high brightness LEDs is still high, each price is about 20 yuan, but LED high-efficiency energy-saving bulbs are not only beautiful, especially green, energy-efficient and safe. For incandescent lamps of the same luminous brightness, the power consumption of LEDs is only 10%-20% of the former; the life of incandescent lamps is generally less than 2000 hours, and the life of LEDs is as long as 100,000 hours. This solid light source with small size, light weight, good directionality, energy saving, long life and various harsh conditions is used in solar city lighting systems and decorative lighting for some special occasions such as mining, diving, rescue and military installations. It is generally cost-effective and will definitely impact the traditional light source market.
4 Conclusion
At present, the ultra-high-brightness LED new high-efficiency energy-saving light bulb, although costly, has been successfully applied to solar city lighting systems, and can be used for lighting in other special occasions. With the expansion of ultra-high-brightness LED production, the cost is further reduced, and its advantages in energy saving and long life are enough to make up for its current high price. Ultra-high-brightness LEDs will become a new type of electric light source for a competitive urban lighting system.
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