1 Introduction
In the power consumption, the proportion of electricity used for lighting to the total power generation: 19% in developed countries and 10% in China. With the development of the economy, China's lighting power consumption will increase by a large proportion, and the research and application of green energy-saving lighting is receiving more and more attention. The development and promotion of the application of energy-saving lamps has become an urgent task. LED lighting was developed under such circumstances.
A light emitting diode (LED) is a semiconductor solid-state light-emitting device that emits ultraviolet light, visible light, and infrared light when a forward current is applied to a PN junction. The luminescence mechanism of the LED is that electrons and holes in the semiconductor material combine at the PN junction to emit photons corresponding to the energy difference between the electrons and the positive charge holes. Different semiconductor materials can be fabricated into LEDs of various wavelengths.
In recent years, with the rapid development of semiconductor epitaxial technology and manufacturing process technology, LED lighting has developed rapidly in foreign countries (especially in developed countries such as the United States and Japan), and the development of LED lighting in China is seriously lagging behind. This article makes a brief analysis and introduction from the development of lighting lamps, the application status of energy-saving lamps, the research and application status of LEDs, research and application development at home and abroad, and application prospects.
2 LED lighting source development
In the 1970s, orange-orange green LEDs were first discovered, but the light efficiency was poor, and epoxy plastics were needed as filters. In 1996, the first breakthrough was made on the blue light. Now, after the invention of the high-brightness LED, the market share of LED has increased significantly. The development of the traffic light market has validated this trend: if a bright LED is used instead of a standard incandescent lamp using a color filter, it will save 90%. Hewlett-Packard invented a flat-topped, conical LED that emits yellow light with a luminous efficacy of 100 lm/W. Now, the research focus of LEDs with nitride as the core material is how to improve the brightness. It is expected to increase its luminous efficiency from 15lm/W to 50lm/W within 5a. The main goal of the ultra-bright blue LED based on InGaN is to increase the luminous efficiency to 100 lm/W by adjusting the nitride, so that it can be used in white super bright LEDs.
Since the successful development of white LED in 1996, its luminous efficiency has been continuously improved. At the beginning of LED development, the light efficiency was only 5lm/W. By 1999, it achieved the equivalent of incandescent light (15lm/W). The GaN chip used in the initial stage emits blue light, and the yellow light of the phosphor is excited by the excitation phosphor, and the blue light of the chip and the yellow light of the phosphor are mixed to form white light. A three-color hybrid module is integrated with three primary color (R, G, B) LED chips. This is another hybrid white LED lamp with a brightness equivalent to 40W incandescent lamps. Later, the luminous efficacy of the white LED is equivalent to the luminous efficiency of the tungsten halogen lamp of 25 lm / W, but it can only be used as a source of local illumination. Recently, Agilient Laboratories of the United States has developed a successful colored LED with a luminous efficacy of 100 lm/W and a white LED with a luminous efficacy of 40-50 lm/W. It is expected that the luminous efficiency of white LEDs will reach 100lm/W in 2005, which is equivalent to the luminous efficacy of fluorescent lamps.
3 characteristics of white LED
Features of white LED: 1) Low voltage drive, minimum driveable with 2V voltage; 2) Small size, generally 3-5mm in diameter, smaller for light illumination; 3) Light weight, good color rendering, color development The index exceeds 90, exceeding the fluorescent lamp, close to the color rendering performance of the incandescent lamp, close to the natural light; 4) good dimming performance, life expectancy, 100,000 h, vibration resistance, not easy to damage, no visual error when the color temperature changes, no production process Mercury and lead pollution will become an efficient energy-saving light source for replacing incandescent and fluorescent lamps.
Compared with other energy-saving lamps, LED lamps have an obvious advantage: no ballasts are used. It is well known that the start of fluorescent lamps requires ballasts. The old ballasts are inductive ballasts with high starting voltage, high noise, high temperature rise, large bulk and heavy energy consumption. Although the use of electronic ballasts is now promoted, the power saving effect is obvious, but it is ultimately energy-intensive and costly. The starting voltage of the LED lamp is the same as the operating voltage, and no ballast is needed at all, thus eliminating the cost of the ballast and the associated energy consumption. The on/off response time of LED lamps is very short, and it is much faster than fluorescent lamps at the level of tens of ns.
Now, a variety of LED lamp series products such as high-voltage AC power supply and low-voltage DC power supply have been developed and formed. Fluorescent lamps mostly work in high-voltage AC power supplies. Although they can use lower DC voltages, they can't work with 5V power supplies like LEDs.
There are few materials used in the manufacture of LEDs, and heavy metal hazardous substances such as mercury and lead are not required in the raw materials, and the environment is not polluted.
The operating current of the LED has little effect on the light efficiency, and even at very low operating currents, it can maintain high light efficiency. The dependence of luminous efficiency and forward current is negatively proportional.
4 LED light source design
Since the power of a single LED is small and the brightness is low, the use of a single LED does not have the practical significance of large space illumination. To this end, multiple LEDs must be assembled together to design a practical LED lighting system, which can have broad application prospects. At present, the world's largest lighting companies (such as Philips, NHK, Panasonic, Osram, etc.) are gathering multiple LEDs together to develop LED lighting systems with different application ranges and specifications.
The design of the LED optical system is as follows: 1) According to the requirements of the illumination object and the luminous flux, determine the shape of the optical system, the number of LEDs and the size of the power; 2) design a plurality of LED lighting tubes into a point light source, a ring light source or a surface light source. The "secondary light source" calculates the illumination optical system according to the combined "secondary light source"; 3) designs the light distribution and control of each LED tube on the "secondary light source". Some people have researched and designed a new multi-chip LED package mode, which contains dozens of LEDs in a single plastic package, which greatly improves the brightness and can be used for conventional lighting.
Although white LEDs can be realized by the mixed light of red, green and blue LEDs, the more promising is the combination of blue LEDs and fluorescent converters, which can emit a wide spectrum at longer wavelengths. Now, InGaN super bright LEDs and fluorescent The conversion material combined with the manufacture of white LED has made great progress, and the light efficiency has exceeded 10lm/W. The key is to use the ultraviolet emitter as the laser source, absorb all the ultraviolet light by using the light absorbing material, and then emit the full visible light. .
When designing the lighting, when the light source meets the requirements of color rendering, selecting a light source with a large pupil brightness will help improve the light environment quality and contribute to lighting energy saving. For LEDs, energy savings can be achieved by increasing the illumination power of the blue wavelength.
5 LED light source combined with solar applications
As an energy-saving and pollution-free electric light source, LED can be combined with green energy to form a true green energy-saving electricity system. The combination with solar energy application is a typical example.
Ancun Industrial Co., Ltd. manufactures a solar white LED street light. The lamp uses a 55W crystal solar cell with 90 high-brightness LEDs. The illumination on the road surface directly below the 3.2m high illumination lamp is 3lx, and the illumination from the lamp 10m can maintain 1lx illumination. LED solar street lights also have excellent weather resistance, temperature tolerance and long working life. The street lamp is equipped with a suitable battery and can maintain power supply even if there is no sunlight for one week.
China's Shenzhen Chaoyang Solar Energy Co., Ltd. has developed a solar night traffic warning light. The flicker frequency is 60-70 times/min. Under cloudy conditions, it can work continuously for 15 days. It uses a solar cell with a power of 0.3W and four yellow/red ultra-brightness power generation diodes with a visibility of more than 1km. Solar LED lights can be widely used in squares, road lighting, architectural exterior lighting, etc. In addition to energy and solar energy, the white LED lighting system can also use wind energy and fuel cells as auxiliary energy sources.
6 LED light source development prospects
At present, the research on LEDs for illumination is mainly concentrated in the field of inorganic white LEDs, and we cannot ignore the research of organic LEDs. Organic LEDs can also emit white light, but white organic LEDs are highly dependent on the illuminating voltage and have low efficiency. However, their potential for improvement is great. Nowadays, the efficacy of organic LEDs has exceeded 60lm/W, the lifetime is over 50h, and the driving voltage is lower than 5V. Unlike LCD displays, it does not require backlighting, which can be very thin and consume less energy. It is believed that the use of organic LEDs as illumination sources is only a matter of time. US experts predict that by 2008, the global market for organic LEDs will reach $2.3 billion.
Using the characteristics of LEDs, combined with new technologies, it is possible to develop lighting systems for different occasions and applications. The luminous efficiency of LEDs will exceed fluorescent lamps in recent years, becoming an energy-efficient light source, and solar energy, wind energy, and fuel cells can be used as energy sources for lighting systems, which greatly saves energy and reduces atmospheric pollution caused by power generation. @AB The production does not use harmful substances such as mercury and lead, which eliminates the environmental pollution of these wastes. Therefore, white LEDs are green lighting products that are environmentally friendly.
As the fourth generation of green energy-saving light source, white LED will replace incandescent and fluorescent lamps, which are highly valued by countries all over the world. Japan is implementing a development plan to make white LEDs 80-100 lm/W. In April 2000, the United States held the "LED Development Strategy Seminar" to promote the development of LED technology. In the face of the rapid development and competition of white LEDs for lighting in the world, China has also strengthened its emphasis on the development and application of white LEDs for lighting. In June 2003, the Ministry of Science and Technology proposed the “Development of Semiconductor Lighting Project†to provide LED development. Guide the funds, try to change the backwardness of the lighting source technology.
Edit: cedar
Outdoor Speakers,Outdoor Speaker System,Outdoor Bluetooth Speakers,Outdoor Wall Mounted Bluetooth Speakers
The ASI Audio Technology Co., Ltd , https://www.asi-sound.com