The application of LED light sources in the field of li […]
The application of LED light sources in the field of lighting is a product of the rapid development of semiconductor light-emitting materials technology and the concept of "green lighting" gradually gaining popularity. "Green lighting" is a new concept proposed in the field of foreign lighting in the late 1980s, and the implementation of "green lighting project" in China. An important step to realize this plan is to develop and promote efficient and energy-saving lighting appliances, save lighting power, reduce the environment and light pollution, and build (build) a high-quality, efficient, economical, comfortable, safe, reliable and beneficial environment lighting system.
LED lighting concept
LEDs, also known as light-emitting diodes, use solid semiconductor chips as light-emitting materials. When a forward voltage is applied to both ends, the carriers in the semiconductor recombine, releasing excess energy and causing photons to emit to produce visible light.
The development history of LED
The application of the principle of semiconductor PN junction light source made LED came out in the early 1960s, first appeared in 1964 red light-emitting diodes, followed by yellow LED. It was not until 1994 that blue and green LEDs were successfully developed. Successfully developed white LED. LEDs are generally used in indicator lights, signal lights, display screens, landscape lighting and other fields due to their inherent characteristics, such as power saving, long life, vibration resistance, fast response, cold light source, etc., which are everywhere in our daily life , Household appliances, telephones, instrument panel lighting, automobile anti-fog lights, traffic lights, etc. However, due to the limitations of poor brightness and high price, it cannot be used as a general light source.
In recent years, with the continuous deepening of people's research on semiconductor luminescent materials, the continuous progress of LED manufacturing processes and the development and application of new materials, ultra-high brightness LEDs of various colors have made breakthrough progress, and their luminous efficiency has improved by nearly 1000 times, the chromaticity has realized all the colors in the visible light band, the most important of which is the emergence of ultra-high-brightness white LEDs, making it possible for LED applications to span the market of high-efficiency lighting sources. It has been pointed out that high-brightness LEDs will be one of the greatest inventions of mankind after Edison invented incandescent light bulbs.
LED light emitting principle
The light-emitting diode is mainly composed of a PN junction chip, electrodes and an optical system. The area of the luminous body-wafer is 10.12mil. At present, large-chip LEDs appear in the world, with a wafer area of 40mil.
The luminescence process consists of three parts: carrier injection under forward bias, recombination radiation and light energy transmission. The tiny semiconductor wafer is encapsulated in a clean epoxy resin. When electrons pass through the wafer, the negatively charged electrons move to the positively charged hole area and recombine with it. The electrons and holes disappear while generating photons. The greater the energy between electrons and holes, the higher the energy of the photons produced. The energy of the photon in turn corresponds to the color of the light. In the visible light spectrum, blue light and purple light carry the most energy, and orange light and red light carry the least energy. Because different materials have different band gaps, they can emit different colors of light.
The mainstream of LED lighting sources will be high-brightness white LEDs. At present, the white light LEDs that have been commercialized are mostly two wavelengths, that is, a blue single crystal chip plus YAG yellow phosphor powder is mixed to generate white light. In the future, three-wavelength white LEDs are more promising, that is, inorganic ultraviolet chips plus red, blue, and green phosphors are used to generate white light. It will replace fluorescent lamps, compact energy-saving fluorescent bulbs, and LED backlights.
Basic characteristics of LED light source
LED single tube power is 0.03 ~ 0.06 watts, using DC drive, single tube driving voltage 1.5 ~ 3.5 volts, current 15 ~ 18 mA, fast response speed, can operate at high frequency. In the case of the same lighting effect, the power consumption is one-eighth of the incandescent bulb and two-half of the fluorescent tube
The use of electronic light field radiates light, the filament is easy to burn, thermal deposition, light attenuation and other shortcomings. The LED lamp is small in size, light in weight, and encapsulated in epoxy resin, which can withstand particularly high-strength mechanical shock and vibration and is not easy to break. The average life span is 100,000 hours. The service life of LED lamps can reach 5 to 10 years, which can greatly reduce the maintenance cost of lamps and avoid the pain of frequent lamp replacement.
Low calorific value, no heat radiation, cold light source, safe to touch: can accurately control the light type and angle of light, soft color, no glare; does not contain mercury, sodium and other substances that may endanger health. The built-in micro-processing system can control the luminous intensity, adjust the luminous mode, and realize the combination of light and art.
The LED is an all-solid luminous body, which is shock-resistant and shock-resistant and is not easily broken. The waste can be recycled without pollution. The light source is small in size and can be combined at will. It is easy to develop into a light, thin, short and small lighting product, which is also easy to install and maintain.
Of course, energy saving is the most important reason for us to consider using LED light sources. Perhaps LED light sources are more expensive than traditional light sources, but it takes one year of energy saving to recover the investment of light sources (meaning: the accumulation of future revenue), so as to obtain 4-9 years Energy saving net income period several times per year.
The application prospects and trends of LED lighting source technology
For a long time, due to the low efficiency of LED light, its application has been mainly concentrated in various display fields. With the emergence of ultra-high brightness LEDs, applications in the field of lighting have become possible. According to the predictions of international authoritative organizations, the 21st century will enter the era of new lighting sources represented by LEDs, known as the fourth generation of new light sources.
Prospects and development trends
At present, lighting consumption accounts for about 20% of the entire power consumption. Greatly reducing lighting power consumption is an important way to save energy. To achieve this goal, the industry has researched and developed many kinds of energy-saving lighting appliances, and achieved certain results. However, the requirements of "green lighting" are far from enough, and the development and application of more efficient, reliable, safe, and durable new light sources is imperative. LED is attracting the world's attention with its inherent superiority. The United States, other countries and Taiwan have predicted the effectiveness of LED lighting. 55% of incandescent lamps and 55% of fluorescent lamps in the United States have been replaced by LEDs, saving $ 35 billion in electricity bills each year and reducing 755 million tons of carbon dioxide emissions each year.
The replacement of 100% incandescent lamps with LEDs can reduce the power generation of 1-2 nuclear power plants and save more than 1 billion liters of crude oil consumption every year. In Taiwan, 25% of incandescent lamps and 100% of fluorescent lamps are replaced by white LEDs, saving 11 billion kWh per year. As early as 1998, the "21st Century Plan" was compiled to conduct practical research on LED light sources for lighting in the new century. In recent years, Nichia Chemical, Toyota Synthetic, SON
Y, Jiayou Electric and other LED lighting products have come out. The terminal voltage of the PN junction of the led lamp bead forms a certain barrier. When the forward bias voltage is applied, the barrier drops, and the majority carriers in the P and N regions diffuse toward each other. Since the electron mobility is much greater than the hole mobility, a large number of electrons will diffuse into the P region, which constitutes the injection of minority carriers in the P region. These electrons recombine with holes in the valence band, and the energy obtained during recombination is released in the form of light energy. This is the principle of PN junction light emission. LED has a history of development for decades, but its application in the field of lighting is still a new technology. With the rapid development of LED technology and the gradual improvement of its luminous efficiency, the application market of LED will be more extensive. Especially in the context of the increasing concern of global energy shortage, the prospect of LED in the lighting market has attracted more global attention. The industry believes that it will become the most promising market in the next 10 years and the largest market will be the largest potential commodity to replace incandescent lamps, tungsten filament lamps and fluorescent lamps.
Main technical problems in lighting applications
In recent years, the luminous efficiency of LEDs is gradually improving. Commercialized devices have reached the level of incandescent lamps. The luminous efficiency of white LEDs used in landscape lamps is close to the level of fluorescent lamps, and is steadily increasing. However, there are still some technical problems in the popularization and application of lighting:
First, the luminous flux needs to be further improved. Using LED as the lighting source must emit more light and must have higher energy efficiency.
Second, there is still a certain gap between the light emitted by the LED and natural light. The led lamp is a chip of electroluminescent semiconductor material, which is cured to the bracket with silver glue or white glue, and then connected to the chip and the circuit board with silver wire or gold wire, and sealed with epoxy resin around to protect the internal core wire Function, and finally install the shell, so the LED lamp has good seismic performance. The incandescent lamp has a very strong yellow light composition, giving a warm feeling. The white light emitted by the white light LED has a component of blue light. Under this light, people's vision is not very natural.
The third is higher prices. This is the main reason affecting the popularity of LED lighting. However, in recent years, due to the improvement of wafer technology, the manufacturing cost is falling sharply. In the past three years, the price of LED has dropped by nearly 50%. It is developing in the direction of high efficiency and low cost. This is the application of LED in the field of lighting. Provided favorable conditions. In addition, a better price-performance ratio can also make up for deficiencies in cost and price.
Application of LED lighting technology in lighting environment
Because LED light sources have high luminous efficiency, low power consumption, long service life, strong safety and reliability, and are beneficial to environmental protection, they have been widely used in urban lighting environments in recent years. It has been used in digital Symphony, guardrail lighting, square lighting, courtyard lighting, floodlighting, underwater lighting series. Many cities use LED light source lighting technology in the construction of urban lighting environment, which has produced good results and accumulated rich experience. Such as Guangzhou Power Building, Guangzhou Hedong Bridge, Guangzhou Industrial and Commercial Bank Building, Zhuhai Yingbin South Road Lighting Project, Central City Lighting Project, Zhengzhou Henan Medical University Overpass, Yanan Road Lighting Project, Hunan Changde Danyang Overpass, Nantong Communication Tower Lighting Project Wait.
With the further development of urbanization throughout the country, the field of lighting environment construction will continue to expand, and the application of LED light sources will also continue to develop. As the fourth-generation new light source, LED has been effectively used in the construction of urban landscape lights, but to replace high-power high-pressure sodium lamps, high-pressure mercury lamps, metal halide lamps and other light sources in the construction and maintenance of street lamps, further needs Research and discussion to seriously solve the technical problems of LED light sources in lighting applications, and LED light source manufacturers need to combine the actual situation of the street light industry to produce new products that meet the needs of street light construction and maintenance, so that the fourth generation of new light sources Play a greater role in the construction of urban lighting.