Abbreviation of English words, main meaning: LED = light emitting diode, which is a solid semiconductor device that can convert electric energy into visible light, and can directly convert electricity into light; LED = large electronic display screen, large electronic display screen; LED = disseminated lupus erythematosus, disseminated lupus erythematosus, a chronic and idiopathic autoimmune disease; Led is the past tense and past participle of lead, meaning "lead, lead"; IATA code of Pulkovo airport in Russia. This entry mainly introduces light emitting diodes.
Basic information
LED application
Advantages of LED 1. Small size
Second, low power consumption.
Third, the service life is long.
Fourth, high brightness and low fever.
Verb (abbreviation of verb) environmental protection
Six, strong and durable
Lighting terminology
LED development
The luminous principle of LED
Dimming control of LED
Operating parameters and efficiency
LED pull-up resistor LED display screen control system
LED classification
The application of LED in street lamps has its inherent advantages and disadvantages.
Basic product information related to LED application
LED application
Advantages of LED 1. Small size
Second, low power consumption.
Third, the service life is long.
Fourth, high brightness and low fever.
Verb (abbreviation of verb) environmental protection
Six, strong and durable
Lighting terminology
LED development
The luminous principle of LED
Dimming control of LED
Operating parameters and efficiency
LED pull-up resistance
LED display screen control system LED classification The application of LED in street lamps has its own advantages and disadvantages.
Basic information
LED (Light Emitting Diode) is a solid-state semiconductor device, which can directly convert electricity into light. The core of LED is semiconductor chip. One end of the chip is attached to the Sanfeng LED on the bracket, one end is the negative electrode, and the other end is connected with the positive electrode of the power supply, so that the whole chip is encapsulated by epoxy resin. The semiconductor wafer consists of two parts, one is a p-type [1] semiconductor, in which holes are dominant, and the other is an n-type semiconductor, in which electrons mainly exist. 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 determines the color of light, and the color of light is determined by the band gap width of the material that constitutes the pn junction. The 2.5-meter-wide resistance plate has been successfully installed and debugged by Cheng Zheng enterprises! Greatly improve the lighting effect
LED application
In view of its own advantages, LED is mainly used in the following aspects: (1) display screen and traffic signal display light source. LED lamps have the characteristics of shock resistance, fast light response, power saving and long service life, and are widely used in various indoor and outdoor display screens, which are divided into full color, tri-color and monochrome display screens. There are more than 100 units under development and production in China. Traffic lights mainly use ultra-high brightness red, green and yellow LEDs. Because of the energy-saving and high reliability of LED lights, traffic lights are being upgraded step by step all over the country, which is a good market opportunity with fast promotion speed and great market demand. (2) Application in automobile industry Automobile lamps include dashboard, audio indicator, switch backlight, reading lamp, external brake lamp, taillight, side lamp, headlight, etc. Incandescent lamps for automobiles are not resistant to impact and impact, easy to be damaged, short in life and need to be replaced frequently. 1987, China began to install high-position brake lights on cars. Due to the fast response speed of LED, drivers can be reminded to brake as soon as possible to reduce rear-end collision accidents. In developed countries, the central rear high-position brake light made of LED has become the standard of automobiles. The LED taillight module introduced by Hewlett-Packard Company in the United States in 1996 can be combined into various taillights at will. In addition, the light source in lighting components such as automobile dashboard can be used as ultra-high brightness light, so LED display screen is gradually adopted. China automobile industry is in a period of great development, which is an excellent opportunity to promote ultra-high brightness LED. In recent years, the annual output value 1 100 million yuan will be 3 billion yuan after five years. (3) The LED backlight with high efficiency side emission is the most eye-catching. As the backlight of LCD, LED has the characteristics of long life, high luminous efficiency, no interference and high cost performance, and has been widely used in electronic watches, mobile phones, BP machines, electronic calculators, credit card machines and so on. With the miniaturization of portable electronic products, LED backlight has more advantages, so the backlight manufacturing technology will develop towards thinner, lower power consumption and uniformity. LED is the key device of mobile phone. An ordinary mobile phone or PHS needs about 10 LED devices, while a color screen and a mobile phone with camera function need about 20 LED devices. At present, the backlight of mobile phones is very large, and 3.5 billion LED chips are used every year. At present, the output of mobile phones in China is very large, and most of the LED backlights are imported, which is an excellent market opportunity for domestic LED products. (4) (4) The early products of LED lighting source have low luminous efficiency, and the light intensity can only reach several tens of MCD, which is suitable for indoor occasions, household appliances, instruments and meters, communication equipment, microcomputers, toys, etc. At present, the direct goal is to replace incandescent lamps and fluorescent lamps with LED light sources, and this substitution trend has begun to develop from local application fields. In order to save energy, Japan is planning a light-emitting diode project (called "Lighting Japan") to replace incandescent lamps. The budget for the first five years is 5 billion yen. If LED is used to replace half of incandescent lamps and fluorescent lamps, the energy equivalent to 6 billion liters of crude oil can be saved every year, which is equivalent to the power generation of five 1.35 × 106kW nuclear power plants, and the generation of greenhouse gases such as carbon dioxide can be reduced, thus improving people's living environment. China also invested 5 billion yuan in 2004 to develop energy-saving and environmental-friendly semiconductor lighting plan [4]. (5) For other applications, such as a kind of flashing shoes popular with children, the built-in LED will flash when walking, and 500 million LEDs are used in Wenzhou alone; Using light-emitting diodes as the power index of electric toothbrushes, according to domestic manufacturers who are putting into production, the company has listed a small number of healthy toothbrushes, and it is estimated that 300 million light-emitting lamps will be needed every year for mass production; The popular LED Christmas lights are novel in shape, colorful, unbreakable and safe to use at low voltage. Recently, they have sold strongly in Southeast Asia, such as Hong Kong, and are widely welcomed by people, threatening and replacing the existing light bulb Christmas market. (6) LED products used for home indoor lighting are becoming more and more popular. LED downlights, LED ceiling lamps, LED fluorescent lamps and LED fiber-optic lamps have quietly entered the family!
[Edit this paragraph] 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.
First, the volume is small.
LED is basically a very small chip, encapsulated in epoxy resin, so it is very small and light.
Second, low power consumption.
The power consumption of LED is very low. Generally speaking, the working voltage of LED is 2-3.6V. The working current is 0.02-0.03A, that is, its power consumption does not exceed 0.1w.
Third, the service life is long.
Under proper current and voltage, the service life of LED can reach 654.38+ million hours.
Fourth, high brightness and low fever.
LED adopts cold light emitting technology, and its calorific value is much lower than that of ordinary lighting.
Verb (abbreviation of verb) environmental protection
LED is made of non-toxic materials, unlike fluorescent lamps, which cause pollution and can be recycled.
Six, strong and durable
LED is 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. LED lamps are highly energy-saving: energy-saving and pollution-free means environmental protection. DC drive, ultra-low power consumption (single tube 0.03-0.06W), electro-optical power conversion close to 100%, the same light efficiency is more than 80% less than that of traditional light source. Longevity: LED light source is called longevity lamp, which means a lamp that never goes out. The solid-state cold light source is encapsulated by epoxy resin, and the lamp body has no loose parts, and there are no shortcomings such as easy burning, thermal deposition and light decay of the filament. The service life can reach 60,000-65,438+10,000 hours, which is more than 10 times longer than the traditional light source. Multi-variation: LED light source can make use of the principle of three primary colors of red, green and blue. Under the control of computer technology, the three colors have 256 gray levels, which can be randomly mixed to produce 256× 256× 256 =16777216 colors, forming a combination of different light colors, and realizing colorful dynamic change effects and various colors. Environmental protection: environmental protection benefits are better. There are no ultraviolet rays and infrared rays in the spectrum, neither heating nor radiation, and the glare is small. In addition, waste can be recycled without pollution and mercury. It is a cold light source and can be safely touched. It belongs to a typical green lighting source. High-tech: Compared with the monotonous luminous effect of traditional light source, LED light source is a low-voltage microelectronic product, which successfully combines computer technology, network communication technology, image processing technology and embedded control technology, so it is also a digital information product and a "high-tech" technology of semiconductor photoelectric devices, with the characteristics of online programming, unlimited upgrade and flexibility.
Lighting terminology
Wavelength: The color intensity of light can be described by data, which is called wavelength. The wavelength of visible light ranges from 380 to 780 nanometers. Unit: nanometer (nm) brightness: brightness refers to the brightness of an object and is defined as the luminous intensity per unit area. Unit: nit light intensity: refers to the brightness of the light source. That is, it represents the physical quantity of visible light radiation intensity emitted by a light source in a certain direction and range. Unit: candlelight (cd) luminous flux: the sum of the energy emitted by the light source and the energy received by human eyes is luminous flux (φ). Unit: Lumens (Lm) Light Efficiency: The luminous flux emitted by the light source divided by the power of the light source. It is an important index to measure the energy saving of light source. Unit: lumens per watt (Lm/w). Color rendering: the degree to which a light source presents an object, that is, the fidelity of color. Usually called "color rendering index". Unit: Ra. Color temperature: at a certain temperature, the color of the light emitted by the light source is the same as that radiated by the blackbody, and the temperature of the blackbody is called the color temperature of the light source. Unit: Kelvin (K). Glare: the visual discomfort caused by objects with extremely high brightness or strong brightness contrast in the field of vision is called glare, which is an important factor affecting the lighting quality. Synchronization: Two or more LED lamps can work normally in a programmed synchronization mode within a specified time, and synchronization is the basic requirement for LED lamps to achieve coordinated changes. Protection grade: IP protection grade is classified according to the dust-proof and moisture-proof characteristics of lamps and consists of two numbers. The first number represents the level of dust prevention and foreign body invasion of lamps (0-6), and the second number represents the sealing degree of lamps against moisture and water invasion (0-8). The higher the number, the higher the protection level.
LED development
The development of LED display screen can be divided into the following stages: the first stage is from 1990 to 1995, mainly monochrome and 16 two-color graphic screens. Used to display text and simple pictures, mainly used in public places such as stations, financial securities, banks and post offices. , as a public information display tool. In the second stage, from 1995 to 1999, dual primary color video screens with 64 and 256 gray levels appeared. The application of video control technology, image processing technology and optical fiber communication technology has pushed LED display screen to a new height. At this time, the large-scale integrated circuit chip for LED display control has also been developed and applied by domestic enterprises. In the third stage, from 1999, a large number of red, pure green and pure blue LED tubes flooded into China. At the same time, domestic enterprises have carried out in-depth research and development work, and the full-color display screens produced by red, green and blue LEDs have been widely used, and a large number of them have entered public places such as stadiums, convention centers and squares, making domestic large screens enter the full-color era. With the rapid development of LED raw material market, 200 1 year surface mount devices came out, mainly used in indoor full-color screens. With its characteristics of high brightness, bright colors and low temperature, the spacing between points can be adjusted at will, which is accepted by demanders at different price points. In just over two years, the product sales exceeded 300 million yuan, and the application market of surface mount full-color LED display screen entered the new century. In order to adapt to the "slimming" plan of the 2008 Olympic Games, Liard developed a surface-mounted two-color display screen, which is widely used in training halls and game timing and scoring systems. In terms of full-color screens in Olympic venues, in order to reduce investment, most full-color screens are detachable, which can be used as live broadcast tools during the Olympic Games and rented after the games, and can also be used as application tools in public places such as performances and national policy announcements to recover costs as soon as possible. As far as the market is concerned, China's entry into WTO and Beijing's successful bid for the Olympic Games have become new opportunities for the development of LED display industry. The domestic LED display market continues to grow. At present, the domestic LED display market share is nearly 95%. The international market capacity of LED display screen is expected to increase by 30% every year. The main manufacturers of LED display panels are concentrated in Japan, North China and other places, and the export share of LED manufacturers can be ignored. According to incomplete statistics, there are at least 150 manufacturers producing full-color screens in the world, among which there are about 30 large companies with complete products.
The luminous principle of LED
Light-emitting diodes are made of III-IV compounds, such as semiconductors such as GaAs (gallium arsenide) and GAAP (gallium phosphide), and their core is a PN junction. Therefore, it has the I-N characteristics of general pn junction, that is, forward conduction, reverse cutoff and breakdown characteristics. In addition, under certain conditions, it also has luminous characteristics. Under DC voltage, electrons are injected from N region to P region, and holes are injected from P region to N region. Part of minority carriers (minority carriers) entering the opposite area and majority carriers (multi-carriers) compound to emit light, as shown in figure 1. Assuming that luminescence occurs in the p region, the injected electrons directly combine with valence band holes to emit light, or are first captured by the luminescence center and then combined with holes to emit light. In addition to this luminescence recombination, some electrons are captured by the non-luminescence center (this center is near the middle of the conduction band and the dielectric band) and then recombine with holes, and the energy released each time is not large enough to form visible light. The greater the ratio of luminous recombination to non-luminous recombination, the higher the quantum efficiency of light. Because recombination emits light in the minority carrier diffusion region, light is generated only within a few microns near the surface of the PN junction. It is proved by theory and practice that the peak wavelength λ of light is related to the band gap width Eg of semiconductor materials in the light-emitting region, that is, the unit of Eg in λ≈ 1240/Eg(mm) is electron volts (eV). If visible light (purple light with a wavelength of 380nm to red light with a wavelength of ~780nm) can be generated, the Eg of the semiconductor material should be between 3.26 ~ 1.63 EV. Light with a longer wavelength than red light is infrared light. At present, there are four kinds of light emitting diodes: infrared, red, yellow, green and blue, but the blue light emitting diode is expensive and not widely used.
Dimming control of LED
Traditionally, the dimming of LED is realized by adjusting the forward current in LED with DC signal or filtered PWM. Reducing LED current will adjust the light output intensity of LED, however, the change of forward current will also change the color of LED, because the chromaticity of LED will change with the change of current. Many applications (such as automobile and LCD TV backlight lighting) do not allow any color drift of LED. In these applications, a wide range of dimming is necessary, because there are different light changes in the surrounding environment, and human eyes are sensitive to small changes in light intensity. Controlling the brightness of the LED by applying PWM signal allows the dimming of the LED to be completed without changing the color.
People often say that PWM dimming is to use a PWM signal to adjust the brightness of LED.
There are three common methods to adjust LED brightness:
(1) Using the set resistor, different conversion resistors are connected in parallel at both ends of the LED drive control IC pin RSET, and a DC voltage is used to set the current of the LED drive control IC pin RSET, thus changing the forward working current of the LED and adjusting the brightness of the LED.
(2) Using PWM technology and PWM control signal, the luminous brightness of LED is adjusted by controlling the duty ratio of LED forward working current.
(3) The simplest method of linear adjustment is to use external setting resistor in LED drive control C to realize LED dimming control. Although this dimming control method is effective, it lacks flexibility and cannot allow users to change the light intensity. Linear adjustment will reduce the efficiency and lead to the color shift of white LED to yellow spectrum. This may be a slight deviation, but it can be detected in sensitive applications. Using digital or PWM LED dimming control method, the pulse duty ratio of LED driving current is changed by pulse width modulation, and the switching frequency is greater than 100HZ. Switching dimming control frequency greater than 100HZ is mainly used to avoid human eyes from feeling dimming flicker. Under the PWM dimming control of LED, the luminous brightness of LED is directly proportional to the pulse duty ratio of PWM. Under this dimming control mode, the luminous color of LED can remain unchanged in the range of high brightness ratio, and the dimming ratio range of LED dimming control with PWM can reach 3000: 1. The dimming control method of linear LED adopts analog dimming control method. Under the analog dimming control, the LED dimming control is realized by adjusting the LED forward working current, and the dimming control range can reach 10: 1. If we want to further reduce the forward working current of LED, it will cause some problems, such as the color of LED will change, and the forward working current of LED cannot be accurately regulated.
Operating parameters and efficiency
Generally speaking, the most common LED operating power is set below 30 to 60 milliwatts. 1999 introduced commercial-grade LED, which can be used continuously under the power input of1w. These LEDs use oversized semiconductor chips to deal with the problem of high power input, and the semiconductor chips are fixed on metal iron sheets to help dissipate heat. In 2002, 5-watt LED appeared on the market, and the efficiency was about 18 to 22 lumens per watt. In September 2003, Cree, Inc. demonstrated its new blue LED, which achieved 35% lighting efficiency at 20 mA. They also made a white LED product with 65 lumens per watt, which was the brightest white LED on the market at that time. In 2005, they demonstrated the prototype of white LED, which achieved a recording efficiency of 70 lumens per watt in a working environment of 350 mA. Nowadays, the working efficiency of organic light-emitting diodes is much lower than that of ordinary LEDs, and the highest is only about 10%. However, the production cost of organic light emitting diodes is much lower. For example, a large array of organic light-emitting diodes can be placed on the screen by a simple printing method to make a color display screen.
LED pull-up resistance
Generally, when an LED works, adding 10mA is enough to make it work normally, so the resistance value is Vo/ 10mA, and Vo is the value of external resistance. For example, a resistance of 500 ohms can be used at a voltage of +5V.
Led display control system
Simply put, it is divided into: synchronous control system (synchronous with computer output); Asynchronous off-line control system (control card stores content and runs off-line) With the rapid development of LED display screen in recent two years, the market of LED control system has also become broader, especially the newly built Vida USB flash drive LED control card in 2009 is currently used the most. Vida USB flash drive LED control card can be connected to a computer through a serial port, and can also be used to transmit information, saving computers, avoiding wiring, supporting analog clocks and flowing borders. Vida USB flash drive LED control card is suitable for all kinds of indoor and outdoor display screens, and has been popular all over the country since its listing. Vida USB flash drive LED control card [2] LED display screen has gradually entered the civilian use, such as the door head screen of various stores, various square screens indoors and outdoors, and various other bar screens. At present, computers must be connected to the display screen to update content, which makes it difficult for a large number of users, especially advertisers, to update programs. The USB flash drive LED control card solves this problem. Using USB flash drive, the most common and cheapest information transmission medium, users can update the displayed content by editing the content with the help of Internet cafes, home or friends' computers. The USB flash drive doesn't need to be plugged into the display screen or its extension cord all the time. After plugging in, the information will be stored in the screen for a few seconds, and the USB flash drive can be pulled out. The USB flash drive LED control card has a common serial communication function, and users can directly connect with the computer if they want to communicate directly. U disk is used to transmit the contents of LED display screen, and has been gradually applied to LED display screens all over the country. LED display control card, also known as LED asynchronous controller, is the core component of LED graphic display. Responsible for receiving picture display information from computer serial port, putting it into frame memory, and generating serial display data and scanning control sequence required by LED display screen according to partition driving mode. The LED display screen mainly displays various characters, symbols and graphics. Screen display information is edited by computer, preloaded into the frame memory of LED display screen through RS232/485 serial port, and then displayed and played screen by screen, in a cycle. The display mode is rich and colorful, and the display screen works offline. LED display screen is widely used in various industries because of its flexible control, convenient operation and low cost.
LED classification
1, according to the luminous color of the LED.
According to the luminous color of LED, it can be divided into red, orange, green (yellow-green, standard green and pure green) and blue light. In addition, some LEDs contain chips of two or three colors. According to whether light-emitting diodes are doped with scatterers, colored or colorless, light-emitting diodes of the above colors can be divided into four types: colored transparent, colorless transparent, colored scattering and colorless scattering. Scattering LEDs and LEDs are used as indicator lights.
2. According to the characteristics of LED light-emitting surface.
According to the characteristics of light-emitting surface of LED, it can be divided into round lamp, square lamp, rectangle, surface LED, side tube and microtubule for surface mounting. The diameter of circular lamp is divided into φ2mm, φ4.4mm, φ5mm, φ8mm, φ 10mm and φ20mm. In foreign countries, light-emitting diodes with a diameter of 3 mm are usually marked as T-1; φ5mm is marked as t-1(3/4); Write φ4.4mm as T- 1( 1/4).
The angular distribution of circular light intensity can be estimated by half-value angle.
From the angle distribution diagram of luminous intensity, there are three types:
(1) high directivity. Generally, it is a pointed epoxy package or a package with a metal reflective cavity, and no scattering agent is added. The half-value angle is 5 ~ 20 or less, which has high directivity and can be used as a local lighting source or combined with a photodetector to form an automatic detection system.
(2) standard type. Usually used as an indicator light, its half-value angle is 20 ~ 45.
(3) Scattering type. This is an indicator lamp with a large viewing angle, with a half-value angle above 45 ~ 90, and a large number of scattering agents.
3. According to the structure of LED.
According to the structure of LED, there are full epoxy package, metal-based epoxy package, ceramic-based epoxy package and glass package.
4. According to the luminous intensity and working current, there are LEDs with ordinary brightness (luminous intensity100 MCD); Luminous intensity between 10 and 100 MCD is called high brightness led. Generally, the working current of LED is in the range of ten milliamps to tens of milliamps, while the working current of low-current LED is below 2mA (the brightness is the same as that of ordinary LED).
In addition to the above classification methods, there are also methods of classification by chip material and classification by function.
[The application of LED in street lamps has inherent advantages and disadvantages.
1. Advantages: 1. As a point light source, if the design is reasonable, LED can directly solve the problems of secondary light emission and light loss that traditional spherical light sources must rely on light; Secondly, the uniformity of the light irradiation surface can be controlled, and theoretically it can be completely uniform in the target area, which can also avoid the light waste of the phenomenon of "light under the lamp" in traditional light sources; Thirdly, color temperature can be selected, which is also an important way to improve efficiency and reduce cost in different applications; Fourth, there is still a lot of room for technological progress. Second, the disadvantages (factors affecting the popularization and application of street lamps) are: the current price is still too high and the luminous flux is low. At present, the price of LED light source with the same illumination design is about four times that of traditional light source (but in street lamp products, the light source part accounts for a small proportion in the total cost, so the cost increase ratio in engineering installation will not be too high, and the application space is still relatively large), which is unbearable for civil use. At present, the design and manufacturing standards are chaotic and the damage rate is high, which affects the life advantage of LED.