LED structure and luminous principle

LED (Light Emitting Diode) is a solid-state semiconductor device, which can directly convert electricity into light. The core of LED is semiconductor chip, namely light emitting diode.

One end of the wafer is attached to the bracket, one end is the negative electrode, and the other end is connected to the positive electrode of the power supply, so that the whole wafer is encapsulated by epoxy resin. The semiconductor wafer consists of two parts, one is a P-type semiconductor, in which holes are dominant, and the other is an N-type semiconductor, mainly electrons. But when these two semiconductors are connected together, a pn junction is formed between them. When the current acts on the chip through the wire, the electrons will be pushed to the P region, where they will recombine with holes and then release energy in the form of photons, which is the principle of LED light emission. The wavelength of light, that is, the color of light, is determined by the material forming the pn junction. At first, LED was used as the indicating light source of instruments. Later, LEDs with various colors were widely used in traffic lights and large-area display screens, which produced good economic and social benefits. Take 12 inch red traffic light as an example. In the United States, 140 watt incandescent lamp with long life and low light efficiency was originally used as the light source to generate white light with 2000 lumens. After passing through the red filter, 90% of the light is lost, leaving only 200 lumens of red light. In the newly designed lamps, Lumileds Company adopted 18 red LED light sources, including circuit loss, * * * consumption 14 watt, which can produce the same light effect. Car signal lamp is also an important field of LED light source application. For general lighting, people need a white light source more. 1998 white LED has been successfully developed. This kind of LED is encapsulated by GaN chip and yttrium aluminum garnet (YAG). GaN chip emits blue light (λp=465nm, Wd=30nm), and the high-temperature sintered YAG phosphor containing Ce3+ emits yellow light with a peak of 550nm after being excited by this blue light. The blue LED substrate is installed in the bowl-shaped reflection cavity and covered with a thin layer of YAG-mixed resin, about 200-500nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LED, by changing the chemical composition of YAG phosphor and adjusting the thickness of phosphor layer, various white lights of 3500- 10000K can be obtained. This method of obtaining white light through blue LED is widely used because of its simple structure, low cost and high technical maturity. In 1960s, scientists and technicians developed LED according to the principle of semiconductor PN junction. The LED developed at that time was made of GaASP material, and its luminous color was red. After nearly 30 years of development, the familiar LED has been able to emit red, orange, yellow, green, blue and other colors of light. However, white LED for lighting has only been developed in recent years. Here, the white LED for lighting is introduced to readers.

Brief introduction of LED application

1. Relationship between visible light spectrum and LED white light. As we all know, the wavelength range of visible light spectrum is 380 nm ~ 760 nm, which is seven colors of light that human eyes can feel-red, orange, yellow, green, cyan, blue and purple, but these seven colors of light are monochromatic. For example, the peak wavelength of red light emitted by LED is 565 nm. There is no white light in the spectrum of visible light, because white light is not monochromatic light, but synthetic light composed of many monochromatic lights, just as sunlight is composed of seven monochromatic lights, and white light in color TV sets is also composed of three primary colors: red, green and blue. Therefore, in order to make LED emit white light, its spectral characteristics should include the whole visible spectral range. However, under the current process conditions, it is impossible to manufacture an LED with this performance. According to people's research on visible light, the white light that people can see needs at least a mixture of two kinds of light, that is, two-wavelength light (blue light+yellow light) or three-wavelength light (blue light+green light+red light). The above two modes of white light need blue light, so taking blue light has become the key technology to make white light, which is the "blue light technology" pursued by major LED manufacturing companies. At present, there are only a handful of manufacturers who have mastered the "blue light technology" in the world, so there is still a process for the promotion and application of white LEDs, especially the promotion of high-brightness white LEDs in China. 2. Technical structure of white LED and white light source. For general lighting, from the process structure, white LED is usually formed by two methods. The first method is to use "blue light technology" and phosphor to form white light; The second is a variety of monochromatic light mixing methods. These two methods have successfully manufactured white light devices. The system for generating white light by the first method is shown in figure 1. In the picture, the LED GaM chip emits blue light (λ p = 465 nm) and is encapsulated with YAG (yttrium aluminum garnet) phosphor. When the phosphor is excited by blue light, it emits yellow light. As a result, blue light and yellow light are mixed to form white light (the structure of LED is shown in Figure 2). The second method is to package chips with different colors of light and produce white light by mixing the colors of light. 3. The application prospect of white LED lighting new light source. In order to illustrate the characteristics of white LED, let's take a look at the current situation of lighting source. Incandescent lamps and tungsten halogen lamps have luminous efficiency of 12 ~ 24 lumens/watt; The luminous efficiency of fluorescent lamps and HID lamps is 50 ~ 120 lumens/watt. White LED: 1998, the light efficiency of white LED is only 5 lumens/watt, 1999, reaching 15 lumens/watt, which is similar to ordinary household incandescent lamps. In 2000, the luminous efficiency of white LED reached 25 lumens/watt, which was similar to that of halogen tungsten lamp. Some companies predict that by 2005, the light efficiency of LED will reach 50 lumens/watt, and by 20 15 years, the light efficiency of LED is expected to reach 150 ~ 200 lumens/watt. At that time, the working current of white LED can reach ampere level. It can be seen that the development of white LED lighting source for writers will become a possible reality. Although incandescent lamps and tungsten halogen lamps for general lighting are cheap, they have low luminous efficiency (the thermal effect of lamps consumes electricity in vain), short service life and heavy maintenance workload. However, if white LEDs are used as lighting, they not only have high luminous efficiency, but also have a long service life (continuous working time is longer than 10000 hours) and hardly need maintenance. At present, German Hella Company has developed airplane reading lamp by using white LED. A street in Canberra, the capital of Australia, has used white LED as street lighting. China's urban traffic management lights are also replacing the early traffic order indicators with white LEDs. It can be predicted that in the near future, white LED will definitely enter the home to replace the existing lighting. LED light source has the advantages of using low-voltage power supply, low energy consumption, strong applicability, high stability, short response time, no pollution to the environment, multi-color luminescence and so on. Although the price is more expensive than the existing lighting equipment, it is still considered that there will be existing lighting equipment.

Led- function

The characteristics and advantages of LED The inherent characteristics of LED determine that it is the most ideal light source to replace the traditional light source, and it is widely used. A small LED is basically a small chip encapsulated with epoxy resin, so it is very small and light. Low-power LED consumes very little power. Generally speaking, the working voltage of LED is 2-3.6V. The working current is 0.02-0.03A That is to say, the power consumption does not exceed 0.1w.. Long service life Under proper current and voltage, the service life of LED can reach 65,438+100,000 hours. High-brightness low-heat environmental protection LED is made of non-toxic materials, unlike fluorescent lamps, which will cause pollution, and LED can also be recycled. Durable LEDs are completely encapsulated in epoxy resin, which is stronger than light bulbs and fluorescent tubes. There is no loose part in the lamp body, which makes the LED not easy to be damaged.

Color temperature and application of color;

(1) Color temperature of light source: People use the absolute temperature of complete radiator equal to or close to the color temperature of light source to describe the color table of light source (the color seen by human eyes when they directly observe the light source), also known as the color temperature of light source. Color temperature is expressed as absolute temperature k, and different color temperatures will make people have different emotional reactions. We generally divide the color temperature of light sources into three categories: A. Warm color light: the color temperature of warm color light is below 3300K K, which is similar to incandescent lamp, with more red components, giving people a warm, healthy and comfortable feeling. It is suitable for families, houses, dormitories, hospitals, hotels and other places, or places with relatively low temperature. B. Warm white light: also called intermediate color, its color temperature is between 3300 K and 5300 K. Warm white light combined with soft light makes people feel happy, comfortable and quiet. Suitable for shops, hospitals, offices, restaurants, restaurants, waiting rooms and other places. C. cool light: also known as daylight color, its color temperature is above 5300K, and the light source is close to natural light, which makes people concentrate. Suitable for offices, conference rooms, classrooms, studios, design rooms, library reading rooms, exhibition windows and other places. Color rendering: the degree to which the light source presents the color of an object is called color rendering, that is, the degree to which the color is realistic. The light source with high color rendering performance is better in color, and the color we see is closer to the natural color. The light source with low color rendering performance is worse for color, and the color difference we see is also greater. Why is there a difference in color development? The key lies in the spectral characteristics of light. The wavelength of visible light is in the range of 380mm to 780mm, that is, the range of red, orange, yellow, green, cyan, blue and purple light we see in the spectrum. If the proportion of all kinds of light contained in the light emitted by the light source is close to natural light, the colors seen by our eyes will be more realistic. We usually use the color rendering index as the representation of color rendering. Under the irradiation of standard light source, the color rendering index of standard color is set to 100. When the color label is illuminated by the test light source, the degree of visual distortion of the color is the color rendering index of the light source. The larger the color rendering index, the smaller the distortion. Conversely, the greater the distortion, the smaller the color rendering index. Different places have different requirements for the color rendering index of light sources. In the International Lighting Association, the color rendering index is generally divided into five categories: Ra, scope of application, 1A >90, art galleries, museums, printing and other industries and places, 2B80-90-90, family, catering, high-end textile processing and similar industries, 2,60-80, office, school, outdoor street lighting, 3.

Development history of LED

Fifty years ago, people knew the basic knowledge that semiconductor materials can emit light. Structure diagram of light emitting diode.

[1], the first commercial diode was produced in 1960. The core of LED is a wafer composed of P-type semiconductor and N-type semiconductor. There is a transition layer between P-type semiconductor and N-type semiconductor, which is called pn junction. In the PN junction of some semiconductor materials, when the injected minority carriers recombine with the majority carriers, the excess energy will be released in the form of light, thus directly converting electric energy into light energy. When reverse voltage is applied to PN junction, it is difficult to inject minority carriers, so it does not emit light. This kind of diode made by injection electroluminescence principle is called light emitting diode, commonly known as led. When working in the forward direction (that is, DC voltage is applied at both ends), when the current flows from the anode of the LED to the cathode, the semiconductor crystal emits different colors of light from ultraviolet to infrared, and the intensity of light is related to the current. High-power LED with high light efficiency and low light attenuation has been widely used in many lighting fields, such as street lamps, industrial and mining lamps, tunnel lamps, spotlights, fluorescent lamps, etc., and has been well received by the industry. 1. adopts solid-state semiconductor chip to self-package, which has high luminous efficiency. The brightness of 1W can reach the effect of 3W of ordinary fluorescent lamp, saving 60% electricity, and has good light attenuation performance and high temperature resistance to pc plastic material extraction. 2. Lower vf value (3. 1v-3.5v) can reduce dissipation power, reduce calorific value and prolong LED working time. 3. The original epoxy resin packaging technology is adopted to emit energy in the form of electrons, and the lumen values of white and warm white can be almost the same. The product has no spot color circle, high color rendering and good consistency. 4. The lens is treated in a special way to ensure that it will not fall off. 5. Use led street lamp, LED lighting, LED spotlight with high power of 60W80W120W160W180W LED decorative lamp LED lighting LED street lamp LED miner's lamp LED lighting LED stage lamp.

Second, the characteristics of LED light source

1. voltage: LED uses low-voltage power supply, and the power supply voltage is between 6-24V, which varies according to different products, so it is a better light source than high-voltage LED.

Safer power supply is especially suitable for public places. 2. Efficiency: Compared with incandescent lamps with the same light efficiency, the energy consumption is reduced by 80%. 3. Applicability: very small, each unit LED die is 3-5mm square, so it can be made into devices with various shapes, which is suitable for changing environments. 4. Stability: 65,438+million hours, and the light attenuation is 50% of the initial value. 5. Response time: The response time of incandescent lamp is millisecond. The response time of LED lamp is nanosecond. 6. Environmental pollution: no harmful metal mercury. 7. Color: You can change the color by changing the current. LED can easily adjust the band structure and band gap of materials by chemical modification, and realize multicolor emission of red, yellow, green, blue and orange. For example, with the increase of current, an LED that is red at low current can turn orange, yellow and finally green. 8. Price: LED is not expensive. 9. Driving: LED can be driven by low-voltage DC, with small load, weak interference and low requirements for use environment. 10. High color rendering: LED has high color rendering and will not cause harm to people's eyes.

Three. Types and development history of monochromatic LED

Light Emitting Diode(LED)

The earliest LED light source based on the principle of semiconductor pn junction was produced in the early 1960s. The material used at that time was GaAsP, which emitted red light (λ p =650nm). When the driving current is 20 mA, the luminous flux is only a few thousandths of lumens, and the corresponding luminous efficiency is about 0. 1 lumen/watt. In the mid-1970s, the introduction of In and N elements led to green light (λ p =555nm), yellow light (λ p =590nm) and orange light (λ p =6 10nm), and the light efficiency was also improved to 1 lumen/watt. In the early 1980s, GaAlAs LED light source appeared, which made the light efficiency of red LED reach 10 lumen/watt. In the early 1990s, two new materials, GaAlInP emitting red and yellow light and GaInN emitting green and blue light, were successfully developed, which greatly improved the light efficiency of LED. In 2000, the light efficiency of the LED manufactured by the former reached 100 lumens/watt in red and orange regions (λ p =6 15nm), while the light efficiency of the LED manufactured by the latter reached 50 lumens/watt in green regions (λ p =530nm).

Fourth, the application of monochromatic light LED

At first, LED was used as the indicating light source of instruments. Later, LEDs with various colors were widely used in traffic lights and large-area display screens, which produced good economic and social benefits. Take 12 inch red traffic light as an example. In the United States, this kind of LED line lamp

In the past, 140W incandescent lamp with long life and low light efficiency was used as the light source to generate 2000 lumens of white light. After passing through the red filter, 90% of the light is lost, leaving only 200 lumens of red light. In the newly designed lamps, Lumileds Company adopted 18 red LED light sources, including circuit loss, * * * consumption 14 watt, which can produce the same light effect. Car signal lamp is also an important field of LED light source application. 1987, China began to install high-position brake lights on cars. Because of the fast response speed of LED (nanosecond level), the driver behind the car can know the driving situation as soon as possible and reduce the occurrence of rear-end collision. In addition, LED lights have been used in outdoor red, green and blue full-color display screens, keychain miniature flashlights and other fields.

Verb (abbreviation of verb) Development of white LED

For general lighting, people need a white light source more. 1998 white LED has been successfully developed. This kind of LED is encapsulated by GaN chip and yttrium aluminum garnet (YAG). GaN chip emits blue light (λ p =465nm, Wd=30nm), and the high-temperature sintered YAG phosphor containing Ce3+ emits yellow light after being excited by this blue light, with a peak value of 550nm. The blue LED substrate is installed in the bowl-shaped reflection cavity and covered with a thin layer of YAG-mixed resin, about 200-500nm. Part of the blue light emitted by the LED substrate is absorbed by the phosphor, and the other part of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LED, by changing the chemical composition of YAG phosphor and adjusting the thickness of phosphor layer, various white lights of 3500- 10000K can be obtained.

6. Comparison and competition between new neon lights and LED lights.

The following is a comparison between neon lights and LED lights, with the latest LED technology, which is not the information you saw on the Internet before. 1.Is the life of LED light source 100000 hours? According to the calculation of 7% light decay, the actual time is only about 50000 hours. According to the light attenuation of 3%, the practical application can reach 80000 hours. 2. won't the 2.led heat up? Yes, it needs heat dissipation. 3. Can 3.LED replace incandescent lamp? The luminous flux, luminous efficiency and color rendering are all ok, but it is too expensive at present and will not decrease in recent years. But the cost of replacing incandescent lamps can be reduced by increasing the luminous flux of products. 4. Can 4.LED be simply used as a common light source? No, to drive the power supply, optics and heat conduction should cooperate. The advantages of the two light sources compared with neon lights have been covered by LED, but the price of LED lights is too high at present. 6. The power supply of two light sources is better than that of low-voltage LED, but the water resistance is poor and the load current is too large. The input current of large particle 1 watt LED single lamp is 350mA. 7. The control technology of two light sources is easier to realize than LED, but neon lights are mature. 8. Compared with LED, the stability of the two light sources is inconsistent, and the neon lamp is quite stable. A few manufacturers can be relatively stable, such as combining CREE and AOD chips and taking the advantages of their respective chips. 9. Both light sources are more expensive than LEDs, but yellow and red are equivalent, and the main expensive one is LED white light. 10. Comparison of two kinds of outdoor light sources Poor waterproof of LED is the fatal weakness of outdoor use. 1 1. Comparison of two light sources on the market at present. The annual output value of global lighting products is 42 billion US dollars (China1500 million US dollars), and the proportion of LED light sources is less than 1%.

7. What is the packaging of led lights?

1package description of led lamp

Simply put, led packaging is the process of packaging led packaging materials into led lamps.

2 led lamp packaging technology

Generally, led packaging has to go through crystal expanding, crystal fixing, welding, glue filling, foot cutting, light splitting, color separation and other processes.

3 led lamp packaging material

The main packaging materials of led are: chip, gold wire, bracket, glue and so on.

4 led lamp packaging equipment

Crystal expanding equipment, crystal fixing machine, welding machine, dispensing machine, drying box, etc. Generally, there are two types: automatic packaging equipment and manual packaging equipment.

Eight, how to judge the quality of led lamp packaging?

Indicators of led lamp: angle, brightness, color (wavelength) consistency, antistatic ability, attenuation resistance, etc. Packaging materials of led lamps: led packaging materials are the direct and basic factors of led lamps. Led lamp is a combination of several main materials, and a good led lamp must be a combination of all packaging materials and production processes. Led lamp packaging technology: Generally, automatic equipment packaging is better than manual packaging, and the technical level of packaging is also the main factor of led lamp packaging, and the products produced by different manufacturers with the same material are very different;

9. What kind of led lights do you need to make an led display?

Appearance of led lights: outdoor led electronic screen mainly adopts direct-entry oval led lights, and indoor led electronic screen mainly adopts surface-mounted led lights. Parameters of led lamp: Brightness varies according to the use environment and other factors. The wavelength of red light is 620 -625 nm, the wavelength of green light is 520 -525 nm, and the wavelength of blue light is 465 -470 nm.

X. Safety requirements for X.LED lamps and lanterns