First, the structure of LED and the principle of illumination
Fifty years ago, people learned about the basics of semiconductor materials that produced light. The first commercial diode was born in 1960. LED is the abbreviation of English light emitting diode. Its basic structure is an electroluminescent semiconductor material placed on a leaded shelf and then sealed with epoxy resin to protect the inner core. The role, so the LED's seismic performance is good.
LED structure diagram as shown below
The core of the LED is a wafer consisting of a p-type semiconductor and an n-type semiconductor. There is a transition layer between the p-type semiconductor and the n-type semiconductor, called a pn junction. In some PN junctions of semiconductor materials, the injected minority carriers recombine with the majority carriers to release excess energy in the form of light, thereby directly converting electrical energy into light energy. The PN junction adds a reverse voltage, and minority carriers are difficult to inject, so they do not emit light. Such a diode fabricated by the principle of injection electroluminescence is called a light-emitting diode, and is generally called an LED. When it is in the forward working state (ie, the forward voltage is applied to both ends), when the current flows from the anode of the LED to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, and the intensity of the light is related to the current.
Second, the characteristics of LED light source
1. Voltage: LED uses low voltage power supply, the power supply voltage is between 6-24V, depending on the product, so it is a safer power supply than using high voltage power supply, especially suitable for public places.
2. Performance: 80% less energy consumption than incandescent lamps with the same efficacy
3. Applicability: Very small, each unit LED small piece is 3-5mm square, so it can be prepared into various shapes and suitable for variable environment.
4. Stability: 100,000 hours, the light decay is the initial 50%
5. Response time: the response time of its incandescent lamp is millisecond, and the response time of LED light is nanosecond.
6. Environmental pollution: no harmful metal mercury
7. Color: Change the current to change color. The light-emitting diode can be easily adjusted by chemical modification method to adjust the energy band structure and band gap of the material to realize multi-color luminescence of red, yellow, green and blue. For example, a red LED with a small current can change to orange, yellow, and finally green as the current increases.
8. Price: The price of LED is relatively expensive. Compared with incandescent lamps, the price of several LEDs can be comparable to the price of an incandescent lamp. Usually, each group of signal lamps needs to consist of 300 to 500 diodes.
Third, the type of monochromatic LED and its development history
The earliest application of the LED light source made by the principle of semiconductor PN junction light was introduced in the early 1960s. The material used at that time was GaAsP, which emitted red light (λp=650 nm). When the driving current was 20 mA, the luminous flux was only a few thousandths of lumens, and the corresponding luminous efficiency was about 0.1 lm/W.
In the mid-1970s, the elements In and N were introduced to produce green light (λp = 555 nm), yellow light (λp = 590 nm) and orange light (λp = 610 nm), and the luminous efficiency was also increased to 1 lm/W.
By the early 1980s, the LED light source of GaAlAs appeared, making the red LED's luminous efficiency reach 10 lumens per watt.
In the early 1990s, the development of two new materials, GaAlInP, which emits red light and yellow light, and GaInN, which emits green and blue light, have greatly improved the light efficiency of LEDs. In 2000, the former made LEDs in the red and orange regions (λp = 615 nm) with a luminous efficacy of 100 lm/W, while the latter made LEDs with a luminous efficacy of 50 lumens in the green region (λp = 530 nm). watt.
Fourth, the application of monochromatic LED
Originally used as an indicator light source for instrumentation, LEDs of various light colors have been widely used in traffic lights and large-area displays, resulting in good economic and social benefits. Take the 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as the light source, which produced 2000 lumens of white light. After passing the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumi leds uses 18 red LED light sources, including circuit losses, and consumes 14 watts of electricity, which can produce the same light effect.
Automotive signal lights are also an important area for LED light source applications. In 1987, China began to install high-position brake lights on cars. Due to the fast response speed (nanoseconds) of LEDs, drivers of trailing vehicles can be informed of driving conditions and reduce the occurrence of rear-end collisions.
In addition, LED lights have been applied in outdoor red, green, and blue full-color displays, and key-type miniature flashlights.
Fifth, the development of white LED
For general lighting, people need a white light source. In 1998, white LEDs were successfully developed. This LED is made by encapsulating a GaN chip and yttrium aluminum garnet (YAG). The GaN chip emits blue light (λp=465 nm, Wd=30 nm), and the Ce3+-containing YAG phosphor prepared by high-temperature sintering is excited by the blue light to emit yellow light with a peak of 550 nm. The blue LED substrate is mounted in a bowl-shaped reflective cavity covered with a thin layer of resin mixed with YAG, about 200-500 nm. The blue portion of the LED substrate is absorbed by the phosphor, and the other portion of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, white light of various colors having a color temperature of 3500 to 10000K can be obtained. (As shown below)
Table 1 lists the current types of white LEDs and their lighting principles. The first product currently commercialized is a blue single-chip plus YAG yellow phosphor, and its best luminous efficiency is about 25 lm/W. YAG is mostly imported from Japan Nichia Corporation, and the price is 2,000 yuan/kg; The second is that Sumitomo Electric has also developed a white LED with ZnSe as the material, but the luminous efficiency is poor.
It can also be seen from the table that some kinds of white LED light sources are inseparable from four kinds of phosphors: yellow powder of tri-color rare earth red, green, blue powder and garnet structure, which is better seen in the future is three-wavelength light. That is, the inorganic ultraviolet light wafer plus RGB three-color phosphor is used to package the LED white light. It is expected that the three-wavelength white light LED has a commercial opportunity this year. However, the particle size requirements of the three primary color phosphors are relatively small, and the stability requirements are also high, and the specific application is still being explored.
Table 1 Types and Principles of White LEDs
Chip number excitation source luminescent material luminescence principle
1
Blue LED
InGaN/YAG
Blue light of InGaN mixed with yellow light of YAG into white light
Blue LED
InGaN/phosphor
Blue light-emitting red, green and blue primary color phosphors of I nGaN emit white light
Blue LED
ZnSe
The blue light emitted by the film layer and the yellow light excited on the substrate are mixed into white light.
Ultraviolet LED
InGaN/phosphor
UV-excited red, green and blue trichromatic phosphors of InGaN emit white light
2
Blue LED
Yellow green LED
InGaN, GaP
Package two chips with complementary color to form a white LED
3
Blue LED
Green LED
Red LED
InGaN
AlInGaP
Three small pieces of three primary colors are packaged together to form a white LED
Multiple multiple color LEDs
InGaN, GaP
AlInGaP
Packing a variety of optical chips throughout the visible light region to form a white LED
Lighting with LED light source, first replace the power-consuming incandescent lamp, and then gradually enter the entire lighting market, will save a lot of power. Recently, white LEDs have reached a single power consumption of more than 1 watt, and the light output is 25 lumens, which also increases its practicability. Tables 2 and 3 list the performance of white LEDs.
Table 2: Progress in the performance of a single white L ED
Year luminous performance (lumen/watt)
Remarks
1998
5
199
15
Incandescent lamp
2001
25
Similar to tungsten halogen lamp
2005
50
estimate
Table 3 Long-term development goals
Single white LED
input power
10 watts
Luminous efficiency
100 lumens / watt
Output light energy
1000 lumens / watt
Sixth, the industry overview
Among the LED industry, Nichia is the first to use the above technology to develop high-brightness LEDs of different wavelengths, as well as the Laser Diode (LD), which is the heavyweight industry owner of the blue LED patent. After obtaining many basic patents such as blue LED production and electrode construction, Nichia has insisted on not providing external authorization, only adopting its own production strategy, and intends to monopolize the market, making the price of blue LED high. However, other manufacturers with production capacity are quite disapproving. Some Japanese LED manufacturers believe that the strategy of Nichia Chemical Co., Ltd. will enable Japan to gradually seize the opportunity of LED industry in Europe, America and other countries in the competition of blue and white LED. Serious damage to the overall Japanese LED industry. Therefore, many operators will do everything possible to develop and produce blue LEDs. At present, in addition to Nichia and Sumitomo Electric, Toyota Synthetic, Luo Mu, Toshiba and Sharp, Cree, the world's three major lighting factories, Philips, Osram and HP, Siemens, Research, EMCORE, etc. have invested in this product. The research and development production has played a positive role in promoting the industrialization and marketization of white LED products.
Fifty years ago, people learned about the basics of semiconductor materials that produced light. The first commercial diode was born in 1960. LED is the abbreviation of English light emitting diode. Its basic structure is an electroluminescent semiconductor material placed on a leaded shelf and then sealed with epoxy resin to protect the inner core. The role, so the LED's seismic performance is good.
LED structure diagram as shown below
The core of the LED is a wafer consisting of a p-type semiconductor and an n-type semiconductor. There is a transition layer between the p-type semiconductor and the n-type semiconductor, called a pn junction. In some PN junctions of semiconductor materials, the injected minority carriers recombine with the majority carriers to release excess energy in the form of light, thereby directly converting electrical energy into light energy. The PN junction adds a reverse voltage, and minority carriers are difficult to inject, so they do not emit light. Such a diode fabricated by the principle of injection electroluminescence is called a light-emitting diode, and is generally called an LED. When it is in the forward working state (ie, the forward voltage is applied to both ends), when the current flows from the anode of the LED to the cathode, the semiconductor crystal emits light of different colors from ultraviolet to infrared, and the intensity of the light is related to the current.
Second, the characteristics of LED light source
1. Voltage: LED uses low voltage power supply, the power supply voltage is between 6-24V, depending on the product, so it is a safer power supply than using high voltage power supply, especially suitable for public places.
2. Performance: 80% less energy consumption than incandescent lamps with the same efficacy
3. Applicability: Very small, each unit LED small piece is 3-5mm square, so it can be prepared into various shapes and suitable for variable environment.
4. Stability: 100,000 hours, the light decay is the initial 50%
5. Response time: the response time of its incandescent lamp is millisecond, and the response time of LED light is nanosecond.
6. Environmental pollution: no harmful metal mercury
7. Color: Change the current to change color. The light-emitting diode can be easily adjusted by chemical modification method to adjust the energy band structure and band gap of the material to realize multi-color luminescence of red, yellow, green and blue. For example, a red LED with a small current can change to orange, yellow, and finally green as the current increases.
8. Price: The price of LED is relatively expensive. Compared with incandescent lamps, the price of several LEDs can be comparable to the price of an incandescent lamp. Usually, each group of signal lamps needs to consist of 300 to 500 diodes.
Third, the type of monochromatic LED and its development history
The earliest application of the LED light source made by the principle of semiconductor PN junction light was introduced in the early 1960s. The material used at that time was GaAsP, which emitted red light (λp=650 nm). When the driving current was 20 mA, the luminous flux was only a few thousandths of lumens, and the corresponding luminous efficiency was about 0.1 lm/W.
In the mid-1970s, the elements In and N were introduced to produce green light (λp = 555 nm), yellow light (λp = 590 nm) and orange light (λp = 610 nm), and the luminous efficiency was also increased to 1 lm/W.
By the early 1980s, the LED light source of GaAlAs appeared, making the red LED's luminous efficiency reach 10 lumens per watt.
In the early 1990s, the development of two new materials, GaAlInP, which emits red light and yellow light, and GaInN, which emits green and blue light, have greatly improved the light efficiency of LEDs. In 2000, the former made LEDs in the red and orange regions (λp = 615 nm) with a luminous efficacy of 100 lm/W, while the latter made LEDs with a luminous efficacy of 50 lumens in the green region (λp = 530 nm). watt.
Fourth, the application of monochromatic LED
Originally used as an indicator light source for instrumentation, LEDs of various light colors have been widely used in traffic lights and large-area displays, resulting in good economic and social benefits. Take the 12-inch red traffic light as an example. In the United States, a long-life, low-efficiency 140-watt incandescent lamp was used as the light source, which produced 2000 lumens of white light. After passing the red filter, the light loss is 90%, leaving only 200 lumens of red light. In the newly designed lamp, Lumi leds uses 18 red LED light sources, including circuit losses, and consumes 14 watts of electricity, which can produce the same light effect.
Automotive signal lights are also an important area for LED light source applications. In 1987, China began to install high-position brake lights on cars. Due to the fast response speed (nanoseconds) of LEDs, drivers of trailing vehicles can be informed of driving conditions and reduce the occurrence of rear-end collisions.
In addition, LED lights have been applied in outdoor red, green, and blue full-color displays, and key-type miniature flashlights.
Fifth, the development of white LED
For general lighting, people need a white light source. In 1998, white LEDs were successfully developed. This LED is made by encapsulating a GaN chip and yttrium aluminum garnet (YAG). The GaN chip emits blue light (λp=465 nm, Wd=30 nm), and the Ce3+-containing YAG phosphor prepared by high-temperature sintering is excited by the blue light to emit yellow light with a peak of 550 nm. The blue LED substrate is mounted in a bowl-shaped reflective cavity covered with a thin layer of resin mixed with YAG, about 200-500 nm. The blue portion of the LED substrate is absorbed by the phosphor, and the other portion of the blue light is mixed with the yellow light emitted by the phosphor to obtain white light. Now, for InGaN/YAG white LEDs, by changing the chemical composition of the YAG phosphor and adjusting the thickness of the phosphor layer, white light of various colors having a color temperature of 3500 to 10000K can be obtained. (As shown below)
Table 1 lists the current types of white LEDs and their lighting principles. The first product currently commercialized is a blue single-chip plus YAG yellow phosphor, and its best luminous efficiency is about 25 lm/W. YAG is mostly imported from Japan Nichia Corporation, and the price is 2,000 yuan/kg; The second is that Sumitomo Electric has also developed a white LED with ZnSe as the material, but the luminous efficiency is poor.
It can also be seen from the table that some kinds of white LED light sources are inseparable from four kinds of phosphors: yellow powder of tri-color rare earth red, green, blue powder and garnet structure, which is better seen in the future is three-wavelength light. That is, the inorganic ultraviolet light wafer plus RGB three-color phosphor is used to package the LED white light. It is expected that the three-wavelength white light LED has a commercial opportunity this year. However, the particle size requirements of the three primary color phosphors are relatively small, and the stability requirements are also high, and the specific application is still being explored.
Table 1 Types and Principles of White LEDs
Chip number excitation source luminescent material luminescence principle
1
Blue LED
InGaN/YAG
Blue light of InGaN mixed with yellow light of YAG into white light
Blue LED
InGaN/phosphor
Blue light-emitting red, green and blue primary color phosphors of I nGaN emit white light
Blue LED
ZnSe
The blue light emitted by the film layer and the yellow light excited on the substrate are mixed into white light.
Ultraviolet LED
InGaN/phosphor
UV-excited red, green and blue trichromatic phosphors of InGaN emit white light
2
Blue LED
Yellow green LED
InGaN, GaP
Package two chips with complementary color to form a white LED
3
Blue LED
Green LED
Red LED
InGaN
AlInGaP
Three small pieces of three primary colors are packaged together to form a white LED
Multiple multiple color LEDs
InGaN, GaP
AlInGaP
Packing a variety of optical chips throughout the visible light region to form a white LED
Lighting with LED light source, first replace the power-consuming incandescent lamp, and then gradually enter the entire lighting market, will save a lot of power. Recently, white LEDs have reached a single power consumption of more than 1 watt, and the light output is 25 lumens, which also increases its practicability. Tables 2 and 3 list the performance of white LEDs.
Table 2: Progress in the performance of a single white L ED
Year luminous performance (lumen/watt)
Remarks
1998
5
199
15
Incandescent lamp
2001
25
Similar to tungsten halogen lamp
2005
50
estimate
Table 3 Long-term development goals
Single white LED
input power
10 watts
Luminous efficiency
100 lumens / watt
Output light energy
1000 lumens / watt
Sixth, the industry overview
Among the LED industry, Nichia is the first to use the above technology to develop high-brightness LEDs of different wavelengths, as well as the Laser Diode (LD), which is the heavyweight industry owner of the blue LED patent. After obtaining many basic patents such as blue LED production and electrode construction, Nichia has insisted on not providing external authorization, only adopting its own production strategy, and intends to monopolize the market, making the price of blue LED high. However, other manufacturers with production capacity are quite disapproving. Some Japanese LED manufacturers believe that the strategy of Nichia Chemical Co., Ltd. will enable Japan to gradually seize the opportunity of LED industry in Europe, America and other countries in the competition of blue and white LED. Serious damage to the overall Japanese LED industry. Therefore, many operators will do everything possible to develop and produce blue LEDs. At present, in addition to Nichia and Sumitomo Electric, Toyota Synthetic, Luo Mu, Toshiba and Sharp, Cree, the world's three major lighting factories, Philips, Osram and HP, Siemens, Research, EMCORE, etc. have invested in this product. The research and development production has played a positive role in promoting the industrialization and marketization of white LED products.
Automobile device for giving light, especially one that has a covering or is contained within something. Lighting should be provided with good lighting and should minimize glare. For the headlamp, in order to meet the above two requirements, use the two conditions of distant light and near light. The distant light is a long distance light beam that is used in the front of the car or not following other cars. It is generated by the main filament in the focal point of the reflector and the power is large, and the beam direction is approximately horizontal. In order to ensure the safety of driving, the distance of light distance (detection and identification of obstacles) should be greater than the braking distance to realize the timely parking. The speed limit is applied in most countries, given that the required distance light intensity is proportional to the four times of the speed.
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