LED light source lighting technology and its application in lighting environment

The application of LED light source in the field of illumination is the product of the rapid development of semiconductor luminescent material technology and the concept of “green lighting”. "Green lighting" is a new concept proposed in the field of foreign lighting in the late 1980s. The implementation of China's "green lighting project" began in 1996. The important steps to achieve this plan are to develop and promote efficient and energy-saving lighting equipment, save lighting power, reduce environmental and light pollution, and establish a lighting system that is high-quality, efficient, economical, safe, reliable and environmentally friendly.

First, LED lighting concept

LED (LighyEmittingDiode), also known as LED, uses a solid semiconductor chip as a light-emitting material. When a forward voltage is applied to both ends, carriers in the semiconductor recombine, releasing excess energy and causing photon emission to generate visible light.

1. The history of LED development

LEDs were fabricated using the principle of semiconductor P·N junction light source. In the early 1960s, red light-emitting diodes first appeared in 1964, followed by yellow LEDs. It was not until 1994 that blue and green LEDs were successfully developed. In 1996, a white LED was successfully developed by Japan Nichia Corporation (Japan).

LEDs are widely used in indicators, signal lights, displays, landscape lighting, etc., because of their inherent characteristics, such as power saving, long life, vibration resistance, fast response, and cold light source. They are everywhere in our daily life. , household appliances, telephones, dashboard lighting, automotive anti-fog lights, traffic lights, etc. However, due to the limitations of its brightness and high price, it cannot be promoted as a universal light source.

In recent years, with the continuous deepening of research on semiconductor luminescent materials, the continuous advancement of LED manufacturing processes and the development and application of new materials (nitride crystals and phosphors), ultra-high brightness LEDs of various colors have made breakthroughs. Progress, its luminous efficiency has increased by nearly 1000 times, and all colors in the visible light band have been achieved in terms of chromaticity. The most important one is the emergence of ultra-high brightness white LEDs, making it possible for LED applications to leap into the high-efficiency lighting source market. It has been pointed out that high-brightness LEDs will be one of the greatest inventions after humans invented incandescent bulbs.

2. LED lighting principle

The light emitting diode is mainly composed of a PN junction chip, an electrode, and an optical system. Its illuminator, the area of ​​the wafer is 10.12 mil (1 mil = 0.0254 mm 2 ), and there are currently large wafer LEDs in the world with a wafer area of ​​40 mils.

The illuminating process consists of three parts: carrier injection under forward bias, composite radiation and light energy transmission. The tiny semiconductor wafer is encapsulated in a clean epoxy. As the electrons pass through the wafer, the negatively charged electrons move to and recombine with the positively charged hole region, and electrons and holes disappear to produce photons. The greater the energy (band gap) 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 spectrum of visible light, the blue light and the purple light carry the most energy, and the orange light and the red light carry the least energy. Since different materials have different band gaps, they can emit light of different colors.

The mainstream of LED lighting sources will be high-brightness white LEDs. At present, commercial white LEDs are mostly two wavelengths, that is, a white light is mixed with a blue single crystal wafer and a YAG yellow phosphor to produce white light. The future is more optimistic about the three-wavelength white LED, which uses inorganic UV wafers with red, blue and green phosphors to produce white light, which will replace fluorescent lamps, compact energy-saving fluorescent bulbs and LED backlights.

3. Basic characteristics of LED light source

a. High luminous efficiency

After decades of technological improvements, LEDs have greatly improved their luminous efficiency. Incandescent lamps, halogen tungsten lamps have a luminous efficiency of 12-24 lumens/watt, fluorescent lamps 50-70 lumens/watt, and sodium lamps 90-140 lumens/watt. Most of the power consumption becomes heat loss. The improved LED light efficiency will reach 50-200 lumens/watt, and its light has good monochromaticity and narrow spectrum. It can directly emit colored visible light without filtering. At present, all countries in the world have stepped up research on LED light efficiency, and their luminous efficiency will be greatly improved in the near future.

b. Less power consumption

LED single tube power 0.03 ~ 0.06 watts, using DC drive, single tube drive voltage 1.5 ~ 3.5 volts, current 15 ~ 18 mA, fast response, high frequency operation. In the same lighting effect, the power consumption is one-eighth of that of an incandescent light bulb. One-half of the fluorescent tube, Japan estimates that if the LED is twice as high as the fluorescent lamp, it replaces half of the Japanese incandescent lamp. Fluorescent light. It can save equivalent to 6 billion liters of crude oil per year. As for the bridge guardrail lamp, the same effect of a fluorescent lamp is more than 40 watts, and the power of each LED is only 8 watts, and can be changed in color.

c. Long service life

The use of electronic light field radiation, 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, and can withstand high-strength mechanical shock and vibration, and is not easily broken. The average life expectancy 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.

d. Strong security and reliability

Low calorific value, no heat radiation, cold light source, can be safely resisted: it can precisely control the light type and illumination angle, soft light color, no glare; no mercury, sodium and other substances that may be harmful to health. The built-in micro-processing system can control the intensity of illumination and adjust the way of illumination to achieve a combination of light and art.

e. Conducive to environmental protection

LED is an all-solid illuminant, which is resistant to shock and impact, and can be recycled without waste. The light source is small in size and can be combined at will. It is easy to develop into a light, thin and short lighting product, and is also easy to install and maintain.

Of course, energy saving is the most important reason for us to consider the use of LED light sources. Maybe LED light sources are more expensive than traditional light sources, but we can recover the investment of light sources with energy saving for one year, so we can get several times of energy saving net income every year for 4 to 9 years. .

Second, the application prospects and trends of LED lighting source technology

For a long time, due to the low light efficiency of LEDs, their applications have mainly focused on various display fields. With the advent of ultra-high brightness LEDs (especially white LEDs), applications in the field of lighting have become possible. According to the prediction 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.

1. Prospects and development trends

At present, lighting consumption accounts for about 20% of the total power consumption, greatly reducing lighting power is an important way to save energy. To achieve this goal, the industry has researched and developed many kinds of energy-saving lighting equipment, and achieved certain results. However, the requirement of “green lighting” is far from enough. It is imperative to develop and apply new light sources that are more efficient, reliable, safe and durable. LEDs are attracting the attention of the world with their inherent superiority. The United States, Japan and other countries and Taiwan have predicted the LED lighting efficiency. The US 55% incandescent lamp and 55% of the fluorescent lamps have been replaced by LEDs, saving 35 billion US dollars in electricity bills every year and reducing 725 million tons of carbon dioxide emissions every year. The replacement of 100% incandescent lamps in Japan with LEDs can reduce the power generation of one or two nuclear power plants and save more than 1 billion liters of crude oil per year. In Taiwan, 25% of incandescent lamps and 100% of fluorescent lamps were replaced by white LEDs, saving 11 billion kWh per year. As early as 1998, Japan compiled the "21st Century Plan" to conduct practical research on LED light sources for lighting in the new century. In recent years, Japan's Nichia Chemical, Toyota Synthetic, SONY, Jiayou Electric, etc. have all come out with LED lighting products. World-renowned lighting companies such as Philips, Osram, GE, etc. have also invested a lot of manpower and resources in the research and development and production of LED lighting products. GE and EMCORE have partnered to form a new company to develop white LEDs to replace incandescent, compact fluorescent, tungsten halogen and automotive lamps. Germany Osram and Siemens cooperate to develop LED lighting systems. Taiwan's current LED production is second only to Japan's prior to the United States. Since 1998, it has invested 600 million Taiwan dollars in related development work.

The history of LED development has been for decades, but the application in the field of lighting is still new technology. With the rapid development of LED technology and the gradual improvement of its luminous efficiency, the LED application market will be more extensive. Especially in the context of the global energy shortage worry, the prospect of LED in the lighting market has attracted worldwide attention. The industry believes that the most promising market and the largest market in the next 10 years will be the largest potential commodity to replace incandescent, tungsten and fluorescent lamps.

2. The main technical problems in lighting applications

In recent years, the luminous efficiency of LEDs is gradually increasing, commercial devices have reached the level of incandescent lamps, and the luminous efficiency of white LEDs used in landscape lights is close to that of fluorescent lamps, and is growing steadily. However, there are still some technical problems in the popularization of lighting applications:

First, the luminous flux needs to be further improved. With LEDs as illumination sources, more light must be emitted and higher energy efficiency must be achieved.

Second, there is still a certain gap between the light emitted by the LED and the natural light. Incandescent lamps have a very strong yellow light composition, giving a warm feeling. The white light emitted by the white LED has a blue light component. Under the illumination of this light, people's vision is not very natural.

Third, the price is higher. This is the main reason that affects the popularity of LED lighting. However, in recent years, due to the improvement of wafer technology, the manufacturing cost is rapidly declining. The price of LED has dropped by nearly 50% in the past three years, and it is developing towards high efficiency and low cost. This is the application of LED in the field of lighting. Provided favorable conditions. In addition, better cost performance can also make up for the lack of cost and price.

Third, the application of LED lighting technology in the lighting environment

LED light source has been widely used in urban lighting environment in recent years due to its high luminous efficiency, low power consumption, long service life, strong safety and reliability, and environmental protection. It has been applied to digital illusion, guardrail lighting, square lighting, courtyard lighting, floodlighting, and underwater lighting. Many cities have used LED light source lighting technology in urban lighting environment construction, which has produced good results and accumulated rich experience.

Such as Guangzhou Electric Power Building, Guangzhou Hedong Bridge, Guangzhou Industrial and Commercial Building, Zhuhai Yingbin South Road Lighting Project, Dongguan Central City Lighting Project, Zhengzhou Henan Medical Grand Overpass, Shanghai Yan'an Road Lighting Project, Hunan Changde Tianyang Bridge, Nantong Communication Tower Lighting engineering, etc.

With the further development of urbanization throughout the country, the construction of lighting environment (including street lamps, landscape lights, art lamps, etc.) will continue to expand, and the application of LED light sources will continue to develop. As the fourth generation of new light source, LED has been effectively applied in the field of urban landscape lighting construction, but it is necessary 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. Research and discussion, seriously solve the technical problems of LED light source in lighting applications, and also need LED light source manufacturers to combine the actual situation of street lamp industry to produce new products that meet the needs of street lamp construction and maintenance, so that the fourth generation of new light sources Play a bigger role in the construction of urban lighting.