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What if you could stick an OLED panel on your wall with a magnetic mat? A detachable OLED (organic light-emitting diode) panel that would just as easily be taken off as stuck on the wall? Reports surfaced on Tuesday that South Korea-based LG Display has fashioned just the thing, a 0.97 mm thick 55" flat OLED TV panel and only 1.9 kilos (4.2 pounds). LG Display showcased the screen in Korea.By comparison, LG Display's existing 55-inch OLED panel is 4.3 mm thick. Engadget's Jon Fingas said that "it raises the possibility of big-screen sets that easily blend into your living room's décor." That's the good news. The sad news is that there is no word about when such displays will make it to retail shops.The unveiling was part of a broader announcement to showcase the company's plans for the future, which center on OLED tech, said Don Reisinger in CNET. The screen was presented as one of the company's future displays at the media event. Using a magnetic mat, the screen can easily be stuck to—or removed from— a wall. To remove the display from the wall, said Reisinger, you peel the screen off the mat. The Yonhap News Agency report carried a photograph of a model gently lifting the detachable wallpaper OLED panel at the event in Seoul on Tuesday. Yonhap News Agency referred to the LG Display screen as a "wallpaper OLED panel." Don Reisinger of CNET referred to it as press-on wallpaper TV.Strategically, the unveiling tells us something about LG Display, said reports; the company appears to view high-end displays as a growth engine. (They released 55-inch, 66-inch and 77-inch OLED models earlier in the year, said Yonhap News Agency.) The showing also indicates that LG Display continues to focus attention on OLED.Reisinger offered reasons for why OLED "is widely believed to be the next frontier." He said, "The technology adds an organic compound layer that allows not only for exceedingly thin screens, but for those displays to be curved. The organic material also emits its own light, eliminating the need for a backlight. That allows for such thin screens and has made OLED a desirable choice not only for televisions, but for a wide range of wearables and other mobile products."While the wall-sticking panel is a delight to view, Ryan Waniata, writing in Digital Trends on Tuesday, expressed his view that "Such a display probably won't be used in a TV anytime in the near future; it's more likely to end up in wearable technology, automobile manufacturing, and commercial applications." Still, he added, "we could conceivably see such technology (paired with an outboard processing unit) becoming the TV of the future."  

Fujifilm Corporation and nano-electronics research institute imec have demonstrated full-color organic light-emitting diodes (OLED) by using their jointly-developed photoresist technology for organic semiconductors, a technology that enables submicron patterning. This breakthrough result paves the way to producing high-resolution and large organic Electroluminescent(EL) displays and establishing cost-competitive manufacturing methods.Organic EL displays are increasingly used for televisions, mobile devices including smartphones as well as wearable devices. Since they can be made thin and flexible, while also offering excellent response time and contrast ratio. It is said that today's products require organic EL displays of high pixel density, i.e. around 200ppi for 4K televisions, 500ppi for full HD mobile devices and even higher density for compact displays for wearable devices. There has been active R&D for organic semiconductors to develop a high-resolution patterning method for organic EL materials to be used in these products.In 2013, Fujifilm and imec jointly developed photoresist technology for organic semiconductors that enables submicron patterning without damaging the organic semiconductor materials, based on photolithography capable of high-resolution patterning on large substrates. There is no need for additional capital investment since an existing i-line exposure system can be used for the new technology. This is why the technology has attracted wide attention since the development announcement with anticipation of a cost-effective way of manufacturing high-resolution organic semiconductor devices.In the latest achievement, Fujifilm and imec produced full-color OLEDs with the photoresist technology for organic semiconductors and successfully verified their performance. Red, green and blue organic EL materials were patterned, each in the subpixel pitch of 20μm, to create full-color OLEDs. An OLED array of 40 x 40 dots at the resolution of 640ppi was realized and illuminated with UV rays to confirm that red, green and blue dots separately emitted light. The emission of red, green and blue lights was also confirmed in a test involving the application of voltage rather than illumination, confirming its correct performance.These results open new opportunities, such as using the novel photolithography in a multiple patterning process. An example would be creating an OLED array that adds a fourth color to red, green and blue, as well as developing previously-unseen devices such as a new sensors that integrate OLED with the organic photodetector.This research result is to be presented at the SID Display Week, one of the world's largest international exhibitions for information displays, held in San Jose, California from May 31 to June 5, 2015.Since the commencement of joint research in November 2012, Fujifilm and imec have broken through the boundary of conventional technology to contribute to the progress of technology associated with organic semiconductors, e.g., developing the photoresist technology for organic semiconductors that enables the realization of high-resolution submicron patterns. The two companies will continue to undertake cutting-edge R&D involving semiconductor materials, process technology and system integration, thereby contributing to resolving challenges faced by the organic electronics industry.

Jake Dyson, son of Dyson founder James, has staked out his corner in the engineering innovation world with a focus on LED solutions, the Jake Dyson Light. He has in turn been doing a rethink on the characteristics and function of a desk light. He proudly states his LED light solution goes past other designers who have tried to cool LEDs with "half-hearted" attempts. Jake said their lights were built to fail. Dyson and team have come up with a light that cools LEDs properly. Benefit to consumers? A light that lasts for 37 years. Conventional lights neglect to protect LEDs from heat, exposing them to temperatures of up to 130°C. This damages the LEDs' phosphorous coating and degrades brightness and color, said his site.His desk lamp solution: CSYS task lights -Operating at 55°C and making use of "heat pipe technology" the Dyson solution can direct heat away from the LEDs. They lose neither quality nor efficiency for 37 years.Eight LEDs provide 587lx of white light for 37 years. Each is in a conical reflector to eliminate glare.How does he know his product lasts for 37 years? The number was calculated based on IES TM-21-11, he said. The 37 years (or 160,000 hours) is based on 12 hours of continual use per day. (IES stands for Illuminating Engineering Society. TM-21-11 provides a method to determine when the useful lifetime of an LED is reached, a point when the light emitted from an LED depreciates to a level no longer considered adequate for a specific application.)What does he mean by heat pipe technology? "Heat is drawn away from the LEDs using technology typically found in satellites. It's dissipated through an aluminium heat sink, which forms the light's horizontal arm," according to the site.Looking back at how this was developed, he said the process involved looking at, analyzing, lighting. The key goal was not to design things that look good, he said, but to try to improve efficiency with engineering. He said he spent some months looking at problems with lighting, and the big problems that stood out were the lack of direction of light. The arm of the light was positioned by springs and pillars and those wear out over time, he said. So wherever you position your light, it would drop.Dyson initiated a mechanism —the light moves up and down and rotates and moves in and out. Where you position the mechanism for light is where it is. The LEDS were also repositioned for an even spread of light.His site said whereas "conventional lights rely on tension to stay in position, CSYS task lights use gravity." The arm moves vertically using a counterweight pulley system inspired by the construction crane. It extends 27.5 cm horizontally along anti-friction bearings. The zinc alloy base rotates through 360°, and is weighted to increase stability. One can position the light where required with the touch of a fingertip. It moves vertically, horizontally and rotationally through 360°. The LEDs use only a fifth of the energy of a conventional halogen bulb. The product prices are listed on the Dyson site.To cool LEDS is critical to the LED market, he said. Gizmag's Nick Lavars noted how "Efforts to keep LED bulbs cool has been a focus for manufacturers working to drag the technology into the mainstream. While LEDs won't get as hot as the incandescent cousins, they do still generate heat, which sees their brightness and color deteriorate over time."

In the article today, we will introduce you all about diodes, what is this component and what are its characteristics, where to use it, etc.   Understand what diodes are and what they do in this video Catalog   I. What is a Diode? II. Diode Characteristics III. Diode Application IV. Diode Types V. Diode Conductive Property VI. Diode Parameters VII. Diode Testing FAQ   I. What is a Diode?   In electronic components, a diode is a device with two terminals. The most common function of diodes is to allow primarily the current to pass in one direction (called forward bias) and reverse blocking (known as reverse bias), which called asymmetric conductance. This characteristic of the current directionality of most diodes is commonly referred to as the rectifying function. The most common diodes made today are semiconductor materials such as silicon or germanium. The package of transistors has glass, plastic, and metal commonly. In the early stage, the vacuum electron diode is an electronic device that can transmit current as unidirectional conduction. There is a PN junction and two lead terminals inside the semiconductor diode and it has unidirectional current conductivity according to the direction of the applied voltage. But the crystal diode is a p-n junction interface formed by the sintering of p-type semiconductor and n-type semiconductor, and a space charge layer is formed on both sides of the interface to form a built-in field. When the applied voltage is zero, the diffusion current caused by the concentration difference between the carriers on both sides of the p-n junction is equal to the drift current caused by the self-built electric field. This is a common characteristic of diodes in normal conditions.   II. Diode Characteristics   1. Forward direction When the forward voltage is applied, it is small in the starting part of the forward characteristic, which is not enough to overcome the blocking effect of the electric field in the PN junction, and the forward current is almost zero, which is referred to as the headband. This forward voltage, which cannot lead the diode, is referred to as a deadband voltage. When the forward voltage is greater than the deadband voltage, the electric field blocking in the PN junction is overcome, and the diode is in conduction, and the current rises rapidly with the increase of the voltage. In the normal current range, the terminal voltage of the diode is almost unchanged at the time of conduction, which is referred to as the forward voltage of the diode. When the forward voltage across the diode exceeds a certain value, the internal electric field is rapidly weakened, in the case of this situation, the current increases rapidly and the diode leads forward, which called threshold voltage, and silicon tube is about 0.5V, germanium tube is about 0.1V, in addition, the forward on-voltage drop of silicon diode and germanium diode is about 0.6~0.8V and 0.2~0.3V respectively.   2. Reverse direction When the applied reverse voltage does not exceed a certain range, the current passing through the diode is the reverse current formed by the minority current carrier drift motion. Because the reverse current is very small, the diode is in a cut-off state. This is also called reverse saturation current or leakage current, and it is greatly affected by temperature. In general, the reverse current of silicon tubes is much smaller than that of germanium tubes. The reverse saturation current of low power silicon tube and low-power silicon tube is in the order of nA and the low-power germanium tube is in the order of μA. When the temperature increases, the number of current carriers increases, and the reverse saturation current increases when the temperature is rising.   3. Breakdown When the applied reverse voltage exceeds a certain value, the reverse current increases suddenly, which is called electric breakdown. The critical voltage that causes the breakdown is called the reverse breakdown voltage of diodes. When the electric breakdown occurs, the diode loses its unidirectional conductivity. If the diode is not overheated by electric breakdown, the unidirectional conductivity will not necessarily be permanently destroyed. After removing the applied voltage, its performance can still be restored. If not, the diode is damaged. Therefore, the reverse voltage should be avoided too high when using diodes.   Reverse: the reverse breakdown of the PN junction is divided into Zener breakdown and avalanche breakdown:   a. Zener breakdown  The reverse breakdown is divided into Zener breakdown and avalanche breakdown according to the mechanism. In the case of high doping concentration, when the width of the barrier region is very small and the reverse voltage is large, the covalent bond structure in the barrier region is destroyed, the shared electron is separated from the covalent bond binding, and the covalent electron-hole is produced, which results in the sharp increase of the current. This phenomenon is called Zener breakdown. If the doping concentration is low, and the width of the barrier is wider, which will not result in Zener breakdown easily.   b. Avalanche breakdown  Another breakdown is avalanche breakdown. When the reverse voltage is increased to a larger value, the external electric field accelerates the electron drift speed in the transition region, thus the valence electron in the covalent bond is collided out of the covalent bond by electric field electrodes, which produces a mobile or free electron-hole pair. The newly generated electron-hole is accelerated by the electric field and then bumped out of other valence electrons again. The carrier increases like an electron avalanche, resulting in a sharp increase in the current, which is called avalanche breakdown. Avalanche breakdown is a phenomenon that can occur in both insulating and semiconducting materials.   Regardless of the breakdown, if the current is not limited, it may cause permanent damage to the PN junction.   4. Voltage drop Voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit due to impedance. Diode voltage drop: forward voltage drop silicon diode (no light-emitting type) is 0.7V, the forward voltage drop of germanium tube is 0.3V. In addition, the forward tube voltage drop of LED will vary with different light-emitting colors. But there are three main colors, the specific reference values are as follows:    red LED is 2.0~2.2V yellow LED is 1.8~2.0V green LED is 3.0~3.2V   The rated current of normal luminescence is about 20mA.   The relation of voltage and current of the diode is not linear, therefore, it is necessary to select resistors properly in parallel with different diodes.   5. Characteristic curve As above mentioned, the diode has a unidirectional conductivity. Applying a forward voltage to the diode, when the voltage value is small, the current is very small, and when the voltage exceeds 0. 6V, the current starts to increase exponentially, which is generally referred to as the opening voltage of the diode. When the voltage reaches about 0.7V, the diode is in a fully conductive state, and this voltage is generally referred to as the conduction voltage of the diode and is indicated by the symbol UD.   For germanium diodes, the turn-on voltage is 0.2V and the on-voltage UD is about 0.3V. A reverse voltage is added to the diode: when the voltage is small, the current is small, and this referred to as the reverse saturation current IS. When the reverse voltage exceeds a certain value, the current begins to increase sharply, called reverse breakdown, and meanwhile, the voltage of this phenomenon occurred is called the reverse breakdown voltage of the diode, which is represented by the symbol UBR. The UBR values of different types of diodes vary greatly, ranging from dozens of volts to kilowatts.     III. Diode Application   1. General Principle The main function of a diode is to allow an electric current to pass in one direction (forward direction) and blocks it in the opposite direction (the reverse direction). Based on this function, the diode can be viewed as an electronic check valve. This unidirectional action is called rectification, which is used to transform alternating current (AC) to direct current (DC).   What's more, diodes also have other complicated behaviors than this simple on-off action(their nonlinear current-voltage characteristics as above mentioned). Diodes can conduct electricity if a certain threshold voltage or cut-in voltage is added in the forward direction (forward-biased). And the voltage drop across a forward-biased diode varies slightly with the current, which is affected by temperature; this effect can be used as a temperature sensor or as a voltage reference. In addition, diodes' high resistance to current flowing in the reverse direction drops to a low resistance sharply when the reverse voltage across the diode reaches a value called the breakdown voltage.    The current-voltage characteristic of semiconductor diodes can be fixed by selecting the semiconductor materials and the doping impurities introduced into the materials during manufacture. And these technical indexes are used to create special-purpose diodes that perform many different functions. For example, diodes are used to regulate voltage, to protect circuits from high voltage surges, to electronically tune radio and TV receivers, to generate radio-frequency oscillations, and to produce light.     2. Operational Principle In this video, we will explore the inner workings and applications of the diode in great detail. Apart from the basic working of the diode, this video also explains V-I characteristics and applications of diode (rectification using Bridge rectifier) with help of animation.   The crystal diode is a PN junction formed by p-type semiconductors and n-type semiconductors, and a space charge layer is formed on both sides of the interface with a self-built electric field. When there is a positive voltage bias, the mutual suppression of the external electric field and the self-built electric field leads to the increase of the carrier diffusion current and then the positive current caused by this interaction between them. When there is a reverse voltage bias, the external electric field and the self-built electric field are further strengthened, forming in a certain reverse voltage range independent of the reverse bias voltage, and the reverse saturation current be generated. When the applied reverse voltage excesses a certain value, the electric field intensity in the space charge layer of PN junction reaches the critical value to cause the multiplying process of carriers, resulting in a large number of electron-hole pairs and a very large reverse breakdown current, which is called a breakdown phenomenon of diodes.     3. Specific Explanations There are many types of diodes, and according to electronic fabrication, the following diodes are often used: Zener diodes for voltage regulators, switching diodes for digital circuits, various for resonance, and so on. The most common diode is the light-emitting diode. Light-emitting diodes (LEDs) are widely used in various electronic products, light sources for optical fiber communication, indicators, and lighting for various instruments. LEDs have many characteristics which can not be compared with ordinary light-emitting devices. These characteristics include safety, high efficiency, environmental protection, long life, fast response speed, small size, and solid structure. And the following are some of their main applications:   1) Application summary   (1) In electronic equipment LEDs are generally used in electronic devices as backlight or display, lighting applications. Displays ranging from large LCD televisions, computer displays, and media players such as MP3, MP4, and mobile phones.   (2) In the automobile and large machinery The light-emitting diode is widely used in automobiles and large machinery. Light-emitting diodes are used in the direction lights, in-vehicle lighting, mechanical equipment instrument lighting, large-light, turn-light, brake light, tail lights, and so on. It is mainly because the response of the light-emitting diode is fast and the service life is long (the service life of the general light-emitting diode is longer than that of the service life of automobiles and large machinery).   (3) In coal mine Owing to the advantages of high efficiency, low energy consumption, long life, strong luminosity and so on, LEDs are used in miner lighting devices. Although not fully popularized, it will be widely used in the near future, and LEDs will replace common light-emitting devices in coal mine applications.   (4) In decoration lights of the city Neon is an important symbol of modern urban prosperity, but there are many shortcomings, such as a short life span. Therefore, there are many advantages in replacing neon with LED. Compared with neon, LEDs not only have a longer life, but also save energy, be easily driven and controlled, and do not need maintenance. It is the inevitable result of LED equipment to replace the neon lamps with LED.   2) Selection of several common diodes   (1) detector diode  Generally, the detector diode is usually a point-contact type germanium diode. The detector with high working frequency, low reverse current, and large forward current should be selected according to the specific requirements of the circuit.   (2) rectifier diode Rectifier diodes are generally planar silicon diodes, used in various power rectifier circuits. When selecting rectifier diode, the parameters such as maximum rectified current, maximum reverse working current, cutoff frequency, and reverse recovery time should be considered. The rectifier diode used in the common series regulated power supply circuit is not strict with the reverse recovery time of cutoff frequency, so long as the maximum rectified current and the maximum reverse working current are selected according to the requirements of the circuit which can meet the requirements.   (3) Zener diode The Zener diode is generally used as a reference voltage source in a regulated power supply or as a protection diode in an overvoltage protection circuit. The selected Zener diode shall meet the main parameters based on the applying requirement. The stable voltage value of the Zener diode shall be the same as the reference voltage value of the application circuit, and the maximum stable current of the Zener diode shall be higher than the maximum load current of the application circuit by about 50%.   (4) switching diode  Switching diodes are mainly used in video recorders, TV sets, DVDs, and other household appliances and electronic equipment, such as switching circuits, detection circuits, high-frequency pulse rectifier circuits, and so on.   Medium-speed switching circuit and detection circuit, it is suitable to choose the 2AK series of ordinary switching diodes. High-speed switch circuits can choose RLS series, 1SS series, 1N series, and 2CK series high-speed switch diode.   According to the main parameters of the application circuit (such as forward current, maximum reverse voltage, reverse recovery time, etc.) to select the specific type of switch diode.   (5) variode When selecting variodes, the parameters such as working frequency, maximum reverse working voltage, maximum forward current, and zero-bias junction capacitance should be considered. A variode with a small reverse leakage current and various junction capacitance should be selected.     IV. Diode Types   There are many kinds of diodes. According to its semiconductor materials, it can be divided into germanium diodes (Ge-diodes) and silicon diodes (Si-diodes). According to its different applications, it can be divided into detector diode, rectifier diode, Zener diode, switching diode, isolation diode, Schottky diode, LED, silicon power-switch diode, rotary diode, and so on.    Semiconductor diodes work mainly on PN junctions. The point-contact type and Schottky type, which are the most common type based on the PN junction, and they also included in the range of general diodes. According to the characteristics of the PN structure(core structure), it can be divided into the point-contact diode, surface-contact diode, and planar diode.   1) point-contact type The point-contact diode is pressed on the surface of a clean semiconductor wafer with a thin metal wire, passing through a pulse current, so that one end of the contact wire is firmly sintered with the wafer to form a PN junction. Due to its point-contact characteristic, only a small current can flow through, thus it is suitable for high frequency and small current circuits, such as radio detection. However, compared with the surface junction type, the point-contact diode has poor forward and reverse characteristics, so it can not be used in high current and rectifier. Because the structure is simple, the price is cheap.   2) surface-contact type The PN junction of surface contact is made by alloy method or diffusion method. As for the surface-contact diode, its area of PN junction is larger, allowing a larger current to across through, it is suitable for the conversion of AC to DC circuit, that is rectifying function of diodes, but it is not suitable for the high-frequency circuit.   3) bond types  A bond diode is formed by melting gold or silver filaments on a single crystal sheet of silicon or germanium. and the characteristics are between the point-contact type diode and the alloy type diode. Compared with the point-contact type, although the PN junction capacitance of the bond diode is slightly increased, and its forward characteristic is particularly excellent. It is used as a switch and sometimes applied to the detection and power supply rectification (not greater than 50mA). In a bond diode, a diode of a fused gold wire is sometimes referred to as a gold bond type, and a diode of a fused silver wire is sometimes referred to as a silver bond type.   4) alloy type PN junctions were fabricated on N-type germanium or silicon single crystal wafers by adding indium, aluminum, and other metals. Small forward voltage drop, suitable for the large current rectifier. The PN junction is not suitable for high-frequency detection and high-frequency rectifier because of its large electrostatic capacity.   5) diffusion type In the high-temperature P-type impurity gas, the single crystal wafer heated with N-type germanium or silicon makes one part of the surface of the single crystal become P-type. Due to the small forward voltage drop of the PN junction, it is suitable for a high current rectifier. In addition, the use of high-current rectifiers has changed from silicon alloy to silicon diffusion.   6) mesa type Although its fabrication method of PN junction is the same as that of diffusion type, only the PN junction and its necessary parts are retained, and the unnecessary part is corroded by chemical. The rest of it takes on a mesa shape, hence its name. The initial production of this type is made of semiconductor materials by diffusion method. Therefore, this type is also called diffusion mesa. It usually used for small current switches.   7) planar type It is named after the surface of the semiconductor is made flat. In a semiconductor single crystal chip (mainly an N-type silicon single crystal chip), a P-type impurity is diffused, and a PN junction formed by selectively diffusing a part of the N-type silicon single crystal chip by a shielding effect of a silicon wafer surface oxide film. Therefore, it is not necessary to use chemicals. In addition, the surface of the PN junction is recognized as a type that having good stability and long service life due to the coating of the oxidized film. Initially, the semiconductor material used is formed by chemical extension, and the planar type is also referred to as an epitaxial planar type.    The planar diode is a kind of special silicon diode, it not only can pass through a large current, but also has stable and reliable performance, and it is widely used in switching, pulse, and high-frequency circuits.   8) alloy diffusion type It is a kind of alloy type. Alloy materials are easily diffused materials, which can be over diffused with the alloy by skillfully mixing impurities so that the proper concentration distribution of impurities can be obtained in the formed PN junctions. This method is suitable for the manufacture of high-sensitivity varactor diodes.   9) epitaxial type A diode formed by the manufacture of a PN junction by using an epitaxial surface length process. Manufacturing requires great skill. Because of its ability to control the distribution of impurities at random, it is suitable for the manufacture of high-sensitivity capacitive diodes.   10) Schottky   The basic principle is that: the formed substrate is used to block the reverse voltage on the contact-surfaces of metals (such as lead) and semiconductors (N-type silicon wafers). Schottky and PN junction have fundamental difference in the principle of rectifying function. Its voltage resistance is only about 40V. Its advantages are: switch speed is very fast: reverse recovery time is particularly short. Therefore, switching diodes and low-voltage high current rectifiers can be made based on this method.   According to application, diodes can be divided as :   1. detector diode  The main function of the detector is to detect the low-frequency signal in the high-frequency signal. It belongs to the point-contact type, so its junction capacitance is smaller and its working frequency is higher, and it is generally made of germanium. In principle, when the modulation signal is extracted from the input signal, usually, and the output current less than the 100mA( the rectifier current 100mA is used as the boundary) is called the demodulation. Its advantages include: the working frequency can reach 400MHz, the forward voltage drop is small, the junction capacitance is small, the detection efficiency is high, and the frequency characteristic is good. In addition to being used for detection, it can also be used for limiting, clipping, modulating, mixing, switching, and other circuits. Furthermore, there are also two diode assemblies dedicated to FM demodulation.   2. rectifier diode In principle, the output from the input AC DC is rectified. The rectified current size (100mA) is usually used as the boundary of the output current greater than the 100mA called a rectifier. Surface junction type, so junction capacitance is larger, generally below 3kHZ. Maximum reverse voltage from 25 volts to 3000 volts a total of 22 volts. Classified as follows: 1 silicon semiconductor rectifier diode 2CZ type, 2 silicon bridge rectifier QL type, 3 for television high voltage silicon stack working frequency near 100KHz 2CLG type.   3. clipper diode  The forward voltage drop of the diode is substantially unchanged after the diode is in conduction (the silicon tube is 0.7V, and the silicon tube is 0.3V). With this characteristic, the amplitude of the signal can be limited to a certain range with this limiting element in the circuit.   Most of the diodes can be used as a clipping component, but there is also a dedicated clipping diode like a protective instrument and a high-frequency Zanner diode. To have a particularly strong effect on limiting the sharp amplitude, a diode typically made of a silicon material. There is also a component set: a number of necessary rectifying diodes are connected in series to form a whole, depending on the need for limiting the voltage.   4. modulation diode It usually refers to the ring modulation dedicated diode. It is a combination of four diodes with good forward characteristics and consistency. Even though other varactor diodes have modulation applications, they are usually used directly as FM.   5. mixer diode  In the frequency range of 500~10000Hz, Schottky type and point-contact type diodes are usually used when diode mixing mode is used.   6. amplifier diode The amplification of a negative resistance device, such as a tunnel diode and a bulk diode, is generally performed with a diode, and also the parametric amplification of the variode. Thus, the amplification diodes generally refer to a tunnel diode, a bulk diode, and a variode.   7. switching diode The resistance of the diode is very small under the forward voltage, which is equivalent to that of an on-on switch; under the action of reverse voltage, the resistance is very large, and in the cut-off state, that is turn off state. All kinds of logic circuits can be formed by using the switching characteristics of diodes.   A logic operation with a small current and a magnetic core excitation switching diode for use in milliamperes. The small current switching diode is usually a point-contact type and a bond diode, and also has a silicon diffusion type, a mesa type, and a planar type diode which can work at high temperature. The advantage of the switching diode is that the switching speed is fast, and the switching time of the Schottky diode is very short, thus it is the ideal switching diode. The 2AK point-contact is used for medium-speed switch circuits; the 2CK-type plane is used for high-speed switching circuits, usually for switches, clipping, clamp bits, or detection circuits, and the Schottky-barrier diode has the advantages of small positive voltage drop, high speed, and high efficiency.   8. variode Low-power diode for automatic frequency control (AFC) and tuning. Other manufacturers also have many other terms. When applying reverse voltage, the electrostatic capacity of the PN junction will change. Therefore, it is used for automatic frequency control, scanning oscillation, frequency modulation, and tuning. Generally, although silicon diffusion diodes are used, special diodes such as alloy diffusion type, epitaxial bonding type, and dual diffusion type can be used, because the electrostatic capacity of these diodes has a very large change rate for voltage. Junction capacitance changes with reverse voltage and replaces variable capacitance, used in tuning circuit, oscillating circuit, phase-locked loop circuit. For example, it is often used in TV high-frequency channel conversion and tuning circuits and mostly made of silicon material.   9. frequency multiplication diode For the frequency multiplication of diodes, the frequency doubling depends on the frequency doubling of the variode and the frequency multiplication of the snap-off diode. The variode used for frequency multiplication is called a variable reactor. Although the variable reactor works the same principle as the variode used in automatic frequency control, the construction of the reactor can withstand high power. Snap-off diode, also called step recovery diode, has a short reverse recovery time when switch on to switch off. If sine waves are applied to snap-off diodes because the on-off time is short, so the output waveform is quickly cut off, it can produce a lot of high-frequency harmonics.   10. Zener diode   This type is based on the reverse breakdown characteristic to be made. The voltage at both ends of the circuit remains basically unchanged, which plays the role of stabilizing the voltage. It is made into a diffusion or alloy type of silicon. Its reverse breakdown characteristic curve changes sharply. Made as a control voltage and a standard voltage component. Diode terminal voltage (also known as Zener voltage) from about 3V to 150V, which can be divided into many grades. In terms of power, there is 200mW to 100W or more. Working in the reverse breakdown state, the dynamic resistance RZ is very small. The two complementary diodes are connected in reverse series to reduce the temperature coefficient, which is turned into a 2DW type.   The p-n junction of Zener diodes is highly doped. And normal diodes will also break down with a reverse voltage but the voltage and sharpness of it may not as well as defined. Also, normal diodes are not designed to operate in the breakdown region, but Zener diodes can reliably operate in this case.   Zener diodes are widely used in electronic devices(almost all kinds) and are one of the basic parts of electronic circuits. It is used to generate low-power stabilized supply rails from a higher voltage and to provide reference voltages for circuits, particularly stabilized power supplies. It is also used to protect circuits from overvoltage, especially electrostatic discharge.   11. PIN diode This is a crystal diode constructed by a layer of intrinsic semiconductors (or low concentration impurity semiconductors) between the P and N regions. When the operating frequency exceeds 100MHz, the diode becomes an impedance element due to the memory effect of minority carriers and the transit time effect in the "intrinsic" layer, it becomes an impedance element because of losing rectifying function, and its impedance value varies with the bias voltage. The impedance of the "intrinsic" region is very high when the bias is zero or the DC reverse bias, and the "intrinsic" region is low impedance due to the carrier injection into the "intrinsic" region when the DC is positive bias. Therefore The PIN diode can be used as a variable impedance element. It is often used in high-frequency switches (microwave switches), phase shift, modulation, amplitude limiting, and other circuits.   12. avalanche diode It is a transistor that can produce high-frequency oscillation under the behavior of applied voltage. The working principle of producing high-frequency oscillation is that the carrier is injected into the crystal by avalanche breakdown. Because the carrier transit chip takes a certain time, the current lags behind the voltage, and the delay time occurs. If the transit time is controlled properly, there will be a dynatron effect in the relationship between current and voltage, which will produce high-frequency oscillation. So it is often used in oscillating circuits in the microwave field.   13. tunnel diode It is a crystal diode based on tunneling effect current as of the main current component. The substrate materials are gallium arsenide and germanium, and the N-type region of the P region is highly doped.    A tunnel diode is a dual terminal active device, and it can be used in low-noise and high-frequency amplifiers and high-frequency oscillators (whose operating frequency can be up to millimeter-wave level) or in high-speed switching circuits.   (Note: Tunneling is the quantum mechanical phenomenon where a subatomic particle passes through a potential barrier that it cannot surmount under the provision of classical mechanics.   Tunneling plays an essential role in several physical phenomena, such as the nuclear fusion that occurs in main sequence stars like the Sun. It has important applications in the tunnel diode, quantum computing, and scanning tunneling microscope. The effect was predicted in the early 20th century, and its acceptance as a general physical phenomenon came mid-century.   Fundamental quantum mechanical concepts are central to this phenomenon, which makes quantum tunneling one of the novel implications of quantum mechanics. Quantum tunneling is projected to create physical limits to the size of the transistors used in microprocessors, due to electrons being able to tunnel past them if the transistors are too small.)   14. step recovery diode It is also a diode with a PN junction. Its structural characteristics are that there is a steep impurity distribution area at the boundary of the PN junction, thus forming a "self-help electric field". The reverse current of the PN junction can be reduced to the minimum value (reverse saturation current) after a "storage time" because of the charge storage effect in the vicinity of the PN junction due to the conduction of a few carriers at the forward bias voltage. The self-help electric field of the step recovery diode shortens the storage time, makes the reverse current cut off quickly, and produces abundant harmonic components. The comb spectrum generation circuit can be designed by using these harmonic components. Fast turn-off (step recovery) diodes are used in pulse and high-order harmonic circuits.   15. Schottky barrier diode It is a metal-semiconductor junction diode with Schottky characteristics. The forward starting voltage is lower. In addition to materials, gold, molybdenum, nickel, titanium and other materials can be used in the metal layer. Its semiconductor materials are silicon or gallium arsenide, mostly N-type semiconductors. This device is conductive by most carriers, so its reverse saturation current is much larger than that of PN junction with minority carrier conduction. Because the memory effect of minority carriers in Schottky diodes is very small, the frequency response of it is limited only by the RC time constant, so it is an ideal device for high frequency and fast switching. Its working frequency can reach 100GHz. And, MIS (metal-insulator-semiconductor) Schottky diodes can be used as solar cells or light-emitting diodes.   It also can be used as a continuation diode in the switching power supply inductance and plays a role in the continuation of the current in the relay and another inductive load.   16. damping diode  Damping diodes are widely used in high-frequency voltage circuits, with high reverse working voltage and peak current, but their forward voltage drop is small. It is a kind of high frequency and high voltage rectifier diodes, and often used in TV line scanning circuits for damping and boost rectifying. The commonly used damping diodes are 2CN1, 2CN2, BSBS44, and so on.   17. transient voltage suppressor(TVS) TVS is used to protect the circuits when having a fast overvoltage. They are divided into two types: bipolar and unipolar, classified by the values of peak power (500W-5000W) and voltage (8.2V~200V).   18. double-base diode (unijunction diode) A three-terminal negative resistive device with two base electrodes and emitter used in an oscillating circuit, has the advantages of easy frequency adjustment and good temperature stability.   19. LED It is made of gallium phosphide and gallium arsenide. Low working voltage, small operating current, uniform luminescence, long life, emitting red, yellow, green, blue monochromatic light. With the development of technology, white light and highlight diode to forming the new industry of LED lighting. It is also used in VCD, DVD, calculators, and other displays.   20. silicon power switching diode The silicon power switching diode has the capability of high-speed conduction and cut-off. It is mainly used for high-power switch or voltage-stabilizing circuit, DC converter, high-speed motor speed-regulating, and high-frequency rectification and free-wheeling, and has the advantages of soft recovery property and strong overload capacity. And it is widely applied to the computer, radar power supply, stepper motor speed-regulation, and so on.     According to characteristic, diodes can be divided as:   Point-contact diodes, classified by forward and reverse characteristic, are as follows:   1. Common point contact diode This kind of diode, is usually used in demodulation and rectifier circuits and is an intermediate product with forward and reverse characteristics, such as SD34, SD46, 1N34A, and so on.   2. High reverse voltage resistance point contact diode A kind of component with maximum peak reverse voltage and the maximum DC reverse voltage, which used in the detection and rectification of high voltage circuits, but this type of diode generally has poor or moderate forward characteristics. In point-contact type germanium diode, there are SD38, 1N38A, OA81, and so on.    3. High reverse resistance point-contact diode Forward voltage characteristics are the same as general diodes. Although its reverse voltage is also particularly high, the reverse current is small. Used in circuits with high input resistance and high resistance load. For example, SD54 and 1N54A belong to high reverse resistance diodes made of germanium material.   4. High conduction point-contact diode It is the opposite of the high reverse resistance type. Its reverse characteristics are poor, but the forward resistance is small. For high conduction point-contact diodes, there are SD56,1N56A and so on. For high conduction bond diodes, it has better properties when operating. When the load resistance is especially low, its rectifier efficiency is good.    V. Diode Conductive Property   The most important characteristic of diodes is unidirectional conductivity. In the circuit, the current can only flow from the positive, flow out from the negative.   1) forward characteristic    In electronic circuits, if the positive electrode of the diode is connected to the high potential terminal and the negative electrode to the low potential terminal, the diode will be switched on. This connection is called forward bias. It must be noted that when the forward voltage applied to both ends of the diode is very small, the diode cannot be switched on, and the forward current flowing through the diode is very weak.    2) reverse characteristic    In the electronic circuit, the positive electrode of the diode is connected to the low potential terminal, and the negative electrode is connected to the high potential terminal. In this case, there is almost no current flowing through the diode, and the diode is in the cut-off state. This connection mode is called reverse bias. When the diode is in reverse bias, there will still be a weak reverse current flowing through the diode, called leakage current. When the reverse voltage at both ends of the diode increases to a certain value, the reverse current will increase sharply, and the diode will lose the unidirectional conductivity, this state is called the breakdown of the diode as forward mentioned.   VI. Diode Parameters   The parameters of the diode are used for indicating the performance of the diode and the technical index of the applications. Different types of diodes have different characteristic parameters, and for beginners, the following main parameters must be understood:   (1) rated forward working current It refers to the maximum positive current allowed by the diode during long-term continuous operation.   (2) maximum surge current  It is an excess forward current that is allowed to flow. It is a transient current, and it is usually about 20 times the rated forward current.   (3) maximum reverse operating voltage When the reverse working voltage at both ends of the diode reaches a certain value, the tube will break down and lose its unidirectional conductivity. In order to keep safe, a maximum reverse working power value is specified. For example, the reverse voltage of an lN4001 diode with a reverse voltage of 50V, and is 1000V for IN4007.   (4) reverse current Reverse current is a kind of current that the diode flows through the diode at a specified temperature and maximum reverse voltage. The smaller the reverse current, the better the unidirectional conductivity of the tube. The reverse current is closely related to the temperature, the reverse current increases twice when the temperature rises 10℃ at one time. In addition, silicon diode has better stability than germanium diode at high temperature.   (5) reverse recovery time When the forward voltage converts into the reverse voltage, the current can not stop at a short time, because it has a delay time, which is called reverse recovery time. It directly affects the switching speed of the diode.   (6) maximum power The maximum power is the voltage applied at both ends of the diode multiplied by the current.    (7) dynamic resistance The ratio of the voltage variation near the static operating point to the variation of the corresponding current in the diode characteristic curve.   (8) frequency characteristic Due to the existence of junction capacitance, when the frequency is up to a certain degree, the capacitance reactance is small enough to make the PN junction short-circuit, resulting in the diode loses unidirectional conductivity and cannot work. The larger the PN junction area is, the larger the junction capacitance is, so it can’t work at high frequency.   VII. Diode Testing   General diodes (including detection diodes, rectifier diodes, damped diodes, switching diodes, continuous diodes) have unidirectional conductivity. It is suitable to use a multimeter to detect the positive and reverse resistance, the electrode of the diode can be identified and the damage of the diode can be estimated.   1. The multimeter is placed in the R×100 barrier or R×1k barrier for polarity discrimination. The two-meter pens are connected with two electrodes of the diode respectively. After one result is measured, the two-meter pens are adjusted to obtain another result. In the two measurements, the large resistance value measured is reverse resistance, and the smaller resistance value measured is forward resistance. In addition, the black meter pen is connected with the positive pole of the diode, and the red meter pen is connected with the negative pole of the diode during a small resistance measurement.   2. In general, the positive resistance of GE diode is about 1kΩ and the reverse resistance is about 300. The resistance of the silicon diode is about 5kΩ and the reverse resistance is infinity. The smaller the forward resistance, the better the reverse resistance. The greater the difference between the positive and reverse resistance values, the better the unidirectional conductivity of the diode. If the positive and reverse resistance values of the diodes are all close to zero or the resistance values are small, the internal breakdown short circuit or leakage damage of the diode is indicated. If the positive and reverse resistance values of the diode are infinite, then the dipole is proved. The pipe is open and damaged.   3. Detection of reverse breakdown voltage(withstand voltage) of the diode can be measured by a transistor DC parameter meter. The method is: when measuring the diode, the "NPN/PNP" selection key of the testing meter should be set to the NPN state, and the negative pole should be inserted into the "e" jack of the testing meter and the positive pole of the diode should insert to the "c" jack, then press the V (BR) key, finally the reverse breakdown voltage of the diode can be detected. Another way is that a megohmmeter and a multimeter are used to measure the reverse breakdown voltage of the diode. When measured, the negative electrode of the diode is connected to the positive pole of the megohmmeter, and the positive electrode of the diode is connected to the negative pole of the megohmmeter, and meanwhile, the voltage across the diode is monitored by a multimeter (placed in the appropriate DC voltage level).    Several Detection methods of Common Diode   1. Detection of a low power crystal diode A. Distinguishing positive and negative electrode   (a) Observe the symbol mark on the shell. Usually, the symbol of the diode is marked on the shell with the one end with the triangular arrow being the positive and the other end is the negative pole.   (b) Observe the color dots on the shell. On the shell of a point-contact diode, it is usually marked with a polar color dot (white or red). One end with a general colored point is a positive pole. There are also diodes marked with color bands, and one end with the color bands is a negative pole. For example, a diode shell with a silver band is the negative pole.   (c) the one end of the black meter pen is the positive pole, and one end of the red meter pen is the negative pole, whichever takes the smaller value.   B. Detecting the maximum reverse breakdown voltage.    For alternating current, the maximum reverse operating voltage is the AC peak voltage the diode receives because it is constantly changing.   2. Detection bidirectional trigger diode Put the multimeter in the corresponding DC voltage block. When testing, shake the mega-meter to measure the VBR value. Finally, comparing VBO with VBR, the smaller the difference between the absolute values, the better the symmetry of the measured bidirectional trigger diode.   3. Detection of transient voltage suppression diode (TVS) The multimeter is used to measure the quality of the tube. According to the method of measuring the common diode, the positive and reverse resistance can be measured for the single-pole TVS. The general forward resistance is about 4kΩ, and the reverse resistance is infinity.   For the bidirectional polar TVS, the resistance between the two pins measured by two-meter pens should be infinite, otherwise, the diode performance is poor or damaged.   4. Detection of high-frequency variable-resistance diodes The difference between the positive and negative of high-frequency resistive diodes and ordinary diodes in appearance is that the color code is different. Ordinary diodes are generally black, while high-frequency resistive diodes are always a light color. Its polarity of the band is similar to that of the ordinary diode, that is, one end with a green band represents a negative pole, and the other end without a green band is a positive pole.   5. Detection of variode Inter-modulation by adjusting the red meter pen and the black meter pen of the multimeter, the resistance value between the two pins of the variode should be infinite. During the measurement, it is found that the multimeter pointer has a slight swing to the right or resistance of zero, indicating that the measured variode has a leakage fault or has broken down.   6. Detection of monochromatic light-emitting diodes A 1.5V dry battery is attached to the outside of the multimeter, and the multimeter is placed in R×10 or R×100 block. This method is equivalent to giving the multimeter a voltage of 1.5V, which increases the detection voltage to 3V (the starting voltage of the LED is 2V). When detecting, rotate the two pins of the LED with the two-meter pens of the multimeter. If the diode performance is good, there must be a normal luminous, at this time, the black pen is connected to the positive pole and the red pen is connected to the negative pole.   7. Detection of Infrared light-emitting diode A. Identify the positive and negative electrodes of infrared LEDs. An infrared LED has two pins, usually, the long pin is positive and the short pin is negative. Because the infrared LED is transparent, the electrode inside the tube and shell are clearly visible. The larger electrode is the negative electrode, and the narrower and smaller one is the positive electrode.   B.Measure the positive and reverse resistance of infrared LED firstly, usually, the forward resistance should be about 30k, reverse resistance should be more than 500k so that the device can be used normally.   8. Detection of IR receiver A. identify pin polarity   (a) Detection in appearance. The common IR receiver appearance color is black. When recognizing pins, facing the light window, from left to right, it is positive and negative respectively. In addition, there is a small oblique plane at the top of the IR receiver, usually a negative pin at one end with the oblique plane and a positive electrode at the other end.   (b) First uses multimeter to judge the positive and negative electrodes of common diodes, that is, to exchange red and black meter pen to measure the resistance between the two pins of the diode twice. Under normal conditions, the obtained resistance values should be various. Taking the smaller resistance, the connected end by the red-meter pen is negative and the black-meter pin is positive.   B. detection performance   The forward and reverse resistance of the IR receiver is measured by a multimeter electric barrier. According to the value of forward and reverse resistance, the quality of the IR receiver can be primarily judged.   9. Laser diode detection The pin arrangement order of the laser diode can be determined according to the method of detecting the forward and reverse resistance of ordinary diodes. However, it is important to note that since the forward voltage drop of the laser diode is larger than that of the ordinary diode, the multimeter pointer only slightly swings to the right when detecting the forward resistance.   FAQ   1. What is diode and its symbol? Diode, an electrical component that allows the flow of current in only one direction. In circuit diagrams, a diode is represented by a triangle with a line across one vertex.   2. What is special about a diode? Some semiconductor junctions, composed of special chemical combinations, emit radiant energy within the spectrum of visible light as the electrons change energy levels. Simply put, these junctions glow when forward biased. A diode intentionally designed to glow like a lamp is called a light-emitting diode, or LED.   3. Are diodes AC or DC? It allows current to flow easily in one direction, but severely restricts current from flowing in the opposite direction. Diodes are also known as rectifiers because they change alternating current (ac) into pulsating direct current (dc). Diodes are rated according to their type, voltage, and current capacity.   4. Why do we use zener diode? Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits. The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.   5. What is unit of diode? A diode is not a measurable quantity. Hence,it does not have a unit. Generally,for a diode,we measure characteristics like forward voltage drop,reverse voltage drop and reverse breakdown voltage which are usually measured in Volts.   6. Do diodes have resistance? Just like a resistor or any other load in a circuit, a diode offers resistance in a circuit. Unlike resistors, though, diodes are not linear devices. This means that the resistance of diodes does not vary directly and proportional to the amount of voltage and current applied to them.   7. Does diode reduce current? Ideally, diodes will block any and all current flowing the reverse direction, or just act like a short-circuit if current flow is forward. Unfortunately, actual diode behavior isn't quite ideal. Diodes do consume some amount of power when conducting forward current, and they won't block out all reverse current.   8. How are diodes classified? Diodes are classified according to their characteristics and are offered in a number of different types, including rectifiers, switching diodes, Schottky barrier diodes, Zener (constant voltage) diodes, and diodes designed for high-frequency applications.   9. What is the most common diode? The most commonly used signal diode is the 1N4148. This diode has a close brother called 1N914 that can be used in its place if you can't find a 1N4148. This diode has a forward-voltage drop of 0.7 and a peak inverse voltage of 100 V, and can carry a maximum of 200 mA of current.   10. What is the difference between a Zener diode and a Schottky diode? As their switching speed is very high, Schottky diodes recover very fast when the current reverses, resulting in only a very small reverse current overshoot. ... A special type of diode, called the Zener diode, blocks the current through it up to a certain voltage when reverse biased.   11. What is difference between Schottky diode and normal diode? In the normal rectifier grade PN junction diode, the junction is formed between P type semiconductor to N type semiconductor. Whereas in Schottky diode the junction is in between N type semiconductor to Metal plate. The schottky barrier diode has electrons as majority carriers on both sides of the junction.   12. Why it is called diode? A diode is called a diode because it has two distinct electrodes (i.e. terminals), called the anode and the cathode. A diode is electrically asymmetric because current can flow freely from the anode to the cathode, but not in the other direction. In this way, it functions as a one-way valve for current.   13. Is a diode the same as a resistor? Key Difference: A diode is a type of electrical device that allows the current to move through it in only one direction. ... A resistor is an electric component that is used to provide resistance to current in the circuit. They are mostly used to produce heat or light.   14. How much voltage can a diode take? Silicon diodes have a forward voltage of approximately 0.7 volts. Germanium diodes have a forward voltage of approximately 0.3 volts. The maximum reverse-bias voltage that a diode can withstand without “breaking down” is called the Peak Inverse Voltage, or PIV rating.   15. Can a resistor replace a diode? Diodes only conduct in one direction whereas resistors conduct in both directions. Without analyzing the actual circuit the results would be unpredictable but, generally speaking, being that diodes & resistors are designed to do different things, substituting one for the other is something you wouldn't want to do.   You May Also Like Characteristics and Functions of Diodes Rectifiers and Filters Notes Simplify Current Monitoring by Using Diode | Power Supply Negative End

This article will introduce you some basic information of LEDs, you will learn what is LED, what are its characterics, how to and where to use it, how many kinds of LEDs are there, and so on. Catalog I. What is LED? 1.1 Brief Introduction 1.2 LED Structure 1.3 LED Limiting Parameters 1.4 LED Electrical Parameters 1.5  LED Optical Parameters II. LED Material III. LED Polarity IV. LED Characteristics V. LED Types VI. LED Trends VII. LED Application VIII. LED Light Decline Reasons IX. Complement: Blue LED FAQ I. What is LED? 1.1 Brief Introduction A tutorial on the basics of using LEDs (light emitting diodes). Polarity, forward voltage and current are discussed. A light-emitting diode (LED) is a kind of semiconductor electronic component that can convert electric energy into light energy. The electronic component appeared as early as 1962, emitting only low-light red light at an early stage, and later developed versions of other monochromatic lights, which now has light throughout visible light, infrared and ultraviolet light, and the luminosity has increased to a fairly high degree. With the development of technology, light-emitting diodes have been widely used in display, TV lighting decoration, and lighting sources. With the rapid progress of LED technology in the 1990s, its luminous efficiency exceeded the incandescent lamp, the intensity of light has reached the candlelight level, but also the color has covered the whole visible spectrum range from red to blue. This technological revolution from LED levels to beyond general-purpose light sources has led to new applications such as automotive signals, traffic lights, large outdoor panchromatic displays, and special lighting sources. The light-emitting diode is abbreviated as LED. It is made of a compound containing Ga, As, P, N, and so on. The making principle of LED is when the electrons and the holes are combined, the visible light can be radiated. It is one of the semiconductor diodes that can convert electrical energy into light energy. Compared with ordinary diodes, light-emitting diodes are composed of a PN junction and have unilateral conductivity. When a forward voltage is applied to the light-emitting diodes, the holes injected from the P region to the N region and the electrons injected from the N region to the P region are combined with the electrons and holes in the N region and the P region in the vicinity of the PN junction, respectively, to produce spontaneous emission fluorescence. The energy states of electrons and holes in different semiconductor materials are different. So when their electrons and holes are combined, the energy released is different, and the more energy is released, the shorter the wavelength of light.  Commonly used light-emitting diodes are red, green, or yellow. The reverse breakdown voltage of light-emitting diodes is greater than 5V. Its forward volt-ampere characteristic curve is steep, it must be used in a series current limiting resistor to control the current through the diode. The current limiting resistance R can be calculated using the following formula: R= (E－UF) / IF E is the power supply voltage, the UF is the forward voltage drop of the LED, and the IF is the normal operating current of the LED. The core portion of the light-emitting diode is a crystal sheet composed of a P-type semiconductor and an N-type semiconductor, and a transition layer is formed between the P-type semiconductor and the N-type semiconductor, referred to as a PN junction. In the PN junction of some semiconductor materials, if the injected minority carriers are combined with the majority carriers, the rest will be released in the form of light, that is, the electric energy is directly converted into light energy.  When the reverse voltage is applied to the PN junction, and the minority carriers are difficult to inject, so that no light is emitted. When the current flows from the LED anode to the cathode, the semiconductor crystal emits light from ultraviolet to infrared colors, and the intensity of the light depends on the current. 1.2 LED Structure In the following, a common LED white light as an example to illustrate the structure of the LED. As shown in Fig. 1 , the LED is mainly composed of the following parts: Fig. 1 LED structure Chip ( light emitting) Support: including substrate and heat dissipation base, pin, etc. (heat dissipation, conduction) Gold wire (conductive) Transparent resin (protecting grains, transmittance) 1.3 LED Limiting Parameters 1) Allowable power (PM): The positive DC voltage added to both ends of the LED and the maximum value of the current that flows through it. Beyond this value, the LED will be heated and damaged. 2) Maximum forward DC (IFM): Maximum positive DC current allowed to be added. Exceeding this value will damage the diode. 3) Maximum reverse voltage (VRM): Maximum reverse voltage allowed. If this value is exceeded, the LED may be corrupted. 4) Working temperature: Making a temperature range based on the requirement that LED works with. When exceeding this range, the LED will not work properly and will greatly reduce efficiency. 1.4 LED Electrical Parameters Fig. 2 wavelength of LED light 1) Spectral distribution and peak wavelength: Light generated by light-emitting diodes is not a single wavelength, and its wave growth body is shown in Fig. 2. It can be seen from the diagram that the intensity of λ =100 wavelengths is the largest, and the wavelength is the peak wavelength. 2) The luminous intensity of IV: Light-emitting diodes usually refers to the light intensity in the normal line direction (for cylindrical light-emitting diodes, the axis is its axis). Due to the luminescence intensity of normal LED is 2, the luminescence intensity is usually candela (MCD). 3) The spectral half-width (1/2): It indicates the spectral purity of the light-emitting tube. It refers to a difference between the two wavelengths corresponding to the peak intensity of the light in Fig. 3. Fig. 3 angular distribution of the luminous intensity of two different types of LED 4) The half-value angle θ1/2 and the angle of view: θ1/2 is the angle between the direction of light intensity value and the axial direction (normal direction) of the axial intensity value, and the half-value angle is twice the angle of view (or half-power angle). Fig. 2 shows the angular distribution of the luminous intensity of two different types of LED. The coordinate of the vertical (normal) AO is the relative luminous intensity, that is, the ratio of the luminous intensity to the maximum luminous intensity. Obviously, the relative luminous intensity of the normal direction is 1, and the larger the angle of the normal direction, the smaller the relative luminous intensity.  And this graph can get a half-value angle or an angle of view. 5) The forward working current (IF): It is the positive value of LED when it is normal. In practice,  you should select an IFM below 0. 6. 6) The forward operating voltage VF: Obtain the working voltage in the parameter table at a given forward current. In general, it is measured under IF=20mA. In VF, the forward voltage of the LED is 1.4 ~3V. And when the external temperature rises, the VF drops. 7) V-I characteristics: The relation between the voltage and current of the LED is shown in Fig. 4. When the forward voltage is less than a certain value (called threshold), the current is very small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the increase of the voltage and is illuminated. The forward voltage, reverse current and reverse voltage of the LED can be obtained from the V-I curve. The reverse leakage current of the forward light emitting tube is lower than 10μA. Fig. 4 relation between voltage and current of LED Light-emitting diodes can be divided into four types: transparent, colored, and colorless. In addition, scattered light-emitting diodes are used to guide lights. (8) Main wavelength λD(nm): LED usually uses wavelength to represent color. The main wavelength is equivalent to the corresponding wavelength of the color seen by the human and is different from the peak wavelength of the luminous wavelength. The unit is nm (nanometer). The following are the wavelength parameters for the various luminous colors LED: Purple: 400～435nm Yellow-green: 560～580nm Blue: 435～480nm Yellow: 580～595nm Blue-green: 480～500nm Green: 595～610nm Green: 500～560nm Red: 610～760nm White: It is usually represented by the color coordinates below, or simply showed with warm white, right white, cold white. (9) Chromaticity diagram x and y It refers to the actual value of the LED glow color in the 2D orthogonal coordinate systems x and y, as shown in the following illustration: Fig. 5 chromaticity coordinate diagram 1.5 LED Optical Parameters Several important aspects of optical parameters of LED are: luminous flux, luminous efficiency, luminous intensity, light intensity distribution, wavelength. Luminous efficiency and luminous flux The luminous efficiency is the ratio of the luminous flux to the electric power, and the unit is generally lm/ W. The luminous efficiency represents the energy-saving characteristic of the light source, which is an important index to measure the performance of the modern light source. Luminous intensity and distribution The intensity of LED luminescence is a characterization of its intensity in a certain direction. Since the intensity of LED varies greatly in different spatial angles, we have studied the intensity distribution of LED. This parameter is of great practical significance and directly affects the minimum viewing angle of the LED display device. For example, the large-scale LED color display in gymnasiums and stadiums, if the distribution range of LED single tube is very narrow, then the audience facing the larger angle of the display screen will see the distorted image. And traffic signs also require a wider range of people to identify. Wavelength For the spectral properties of LED, we mainly look at whether its monochromatic property is good, and we should note that the main colors such as red, yellow, blue, green, white LED are pure or not. Because in many cases, such as traffic lights, the color requirements are relatively strict, but it is observed that in some LED lights, in reality, green looks blue and red is dark red. From this point of view, it is necessary and meaningful to study the spectral properties of LED. II. LED Material Generally, the five main raw materials of LED are wafer, bracket, silver glue, gold wire, epoxy resin. In 1993, at that time, Shuji Naka mura, who worked at Nichia Corporation in Japan, invented a blue light LED with commercial application value based on wide-gap semiconductor material nitride (GaN) and silicon nitride (InGaN), which was widely used in the late 1990s. In theory, the blue LED combined with the original red LED and the green LED can produce white light LED, but the white light LED is rarely made in that way. Most of the current white-light LED is made by covering the blue LED (near-UV, wavelength 450nm~470nm) with a yellowish phosphor coating, this yellowish phosphor is usually made by grinding the cerium-doped yttrium aluminum garnet (Ce3: YAG) crystal into powder and mixing it in a dense adhesive. When a LED chip emits blue light, some of the blue light is efficiently converted by this crystal into a mostly yellow light with a wider spectrum (the spectral center is about 580nm). Since the yellow light can stimulate the red and green light receptors in the naked eye, with the blue light, so that it looks like white light when these colors mixed, and its color is often referred to as moonlight. The method of making a white light LED was developed by Nichola Corporation and used in the production of white light LED from 1996. To adjust the color of the light yellowish light, it is possible to replace the Ce doped with the Ce3 +: YAG with other rare-earth elements, or even in a manner that replaces part or all of the aluminum in the YAG. Based on the characteristics of its spectrum, red light and green light are not as obvious as the broad-spectrum light source illuminated. In addition, due to the variation of the production conditions, the color temperature of the finished product of the LED is not uniform, therefore, the characteristics of the finished product should be distinguished during the production process. Another method of making a white LED is like a fluorescent lamp. An LED that emits near-ultraviolet light is coated with a mixture of two phosphors, one is europium which emits red light and blue light, and the other is copper and aluminum-doped with ZnS which emits green light. However, the epoxy resin in the adhesive will be cracked and deteriorated caused by the ultraviolet rays, the production difficulty is high, and the service life is also shorter. In contrast to that first method, it is less efficient (producing more heat) but its spectrum is better and the light looks better.  III. LED Polarity One of the longers of the two leads of the light-emitting diode is the positive pole, which should be connected to the positive pole of the power supply. Some LED leads are the same length, but there is a convex tongue on the shell, the lead near the small tongue is positive. LED Unidirectional Conductivity The LED can only be turned on in one direction, called forward bias, when the current flows, electrons, and holes recombine to emit monochromatic light, which is an electroluminescent effect, and the wavelength of the light and the color is related to the type of semiconductor material used and the element impurities to be incorporated. It has the advantages of high efficiency, long service life, difficult breakage, high switching speed, high reliability, and so on. The light-emitting efficiency of the white LED has been obviously improved in recent years. IV. LED Characteristics Compared with the incandescent bulb and the neon lamp, the light-emitting diode is characterized in that the working voltage is very low, and the working current is small, the impact resistance and the anti-seismic performance are good, the reliability is high, and the service life is long. The intensity of the light-emitting can be conveniently modulated by the intensity of the current passing through the modulation. Due to these features, the light-emitting diode is used as a light source in some photoelectric control devices and is used as a signal display in many electronic devices. Voltage LED uses a low-voltage power supply, the supply voltage is between 3~24V DC, depending on the product requirement, there are a few DC 36V or DC 40V, so it is a safer power supply than the use of high-voltage power supply, especially suitable for public places. Energy consumption The energy consumption is 80% less than the incandescent lamp with the same light efficiency and 40% less than the energy-saving lamp. Applicability Because of its small size, each unit of LED is a square of 3~5mm, so it can be fabricated into devices of various shapes and is suitable for the variable environments. Stability 100,000 hours, light attenuation is 50% of the initial. Response time The response time of the incandescent lamp is milliseconds and the response time of the LED lamp is nanosecond. Pollution No harmful metal mercury, etc. Color The red, yellow, green, and blue-orange multicolor luminescence can be realized by adjusting the energy band structure and the bandgap of the material conveniently through chemical modification. The operation voltage of the red light tube is small, and the operation voltage of red, orange, yellow, green, and blue light-emitting diodes is increased in turn. V. LED Types 1. Depending on the different packaging of the LED, the luminous surface and characteristics of the LED can be roughly divided into the following types: 1) Plug-in LED Plug-in LED, in addition to the common two-terminal monochrome LED, also includes three-terminal dual-color LED and four-terminal RGB full-color LED. 2) Surface-mount LED A surface-mount LED is usually available in 0402, 0603, 0805, 1206, and so on, in monochrome, two-colour, and RGB full-color type. 3) High power LED This type of LED is usually used for lighting source, and most of it is white-emitting LED. 4) LED digital tube By making more than one LED into each field and forming a characteristic letter or combination, you can display the 0/9 or English letters) or the bar-type to indicate progress or scale. 5) LED matrix screen The matrix form of LED can display Chinese and English letters. For example, the manufacturer's LED display screen is composed of these dot matrix screen modules. According to color, it can be monochrome, double color or RGB full-color type. 6) Smart LED This type of LED includes not only a LED core, but also a control circuit, IC, for specific functions, such as blinking flash. Or bus addressing controls the color of each point, and so on. 7) Special LED This kind of LED emits lights that are invisible to human eyes, such as infrared, ultraviolet, and so on. In daily life, we use the remote control as this kind of LED lamp. 2. Light-emitting diodes can also be divided into ordinary monochromatic light-emitting diodes, high brightness light-emitting diodes, ultra-high brightness light-emitting diodes, chronotropic light-emitting diodes, scintillation light-emitting diodes, voltage-controlled light-emitting diodes, infrared light-emitting diodes, and negative resistance light-emitting diodes, etc. There are two control modes of LED: constant current and constant voltage, and there are many dimming modes, such as analog dimming and PWM dimming. Most of the LEDs are controlled by constant current, so that the current of LED can be kept stable, and it is not easy to be affected to extend the service life of LEDs. Ordinary monochromatic light-emitting diode Ordinary monochromatic light-emitting diodes have the advantages of small volume, low operating voltage, small working current, uniform and stable luminescence, fast response speed, and long service life, and can be driven by various DC, AC, and pulse power sources. It belongs to the current-controlled semiconductor device, it needs to be connected to an appropriate current limiting resistor. The light-emitting color of ordinary monochromatic light-emitting diodes is related to the wavelength of light-emitting, and the wavelength of light-emitting depends on the semiconductor materials used in the manufacturing process. The wavelengths of red light-emitting diodes, amber light-emitting diodes, orange light-emitting diodes, and yellow light-emitting diodes are generally 650~700nm, 630~650nm, and 610~630nm respectively, and yellow light-emitting diodes are usually 585nm, green light-emitting diodes typically have a wavelength of 555~570nm. High brightness monochromatic light-emitting diode The semiconductor materials used in high brightness monochromatic light-emitting diodes and ultra-high brightness monochromatic light-emitting diodes are different from those of ordinary monochromatic light-emitting diodes, so the intensity of light-emitting is also different. Typically, high brightness monochromatic light-emitting diodes use materials such as gallium arsenide (GaAlAs) and ultra-high brightness monochromatic light-emitting diodes use phosphonium gallium arsenide (GaAsInP), etc. Common monochromatic light-emitting diodes use gallium phosphide (GaP) or phosphogallium arsenide (GaAsP). Variable color light-emitting diode The variable color light-emitting diode is a light-emitting diode capable of converting light-emitting colors. The color type of the variable color light-emitting diode can be divided into two-color light-emitting diodes, three-color light-emitting diodes, and multi-color (red, blue, green, and white) light-emitting diodes. According to the number of pins, the variable color light-emitting diode can be divided into two-terminal variable color light-emitting diode, three-terminal variable color light-emitting diode, four-terminal variable color light-emitting diode, and a six-terminal variable color light-emitting diode. Flashing light-emitting diode The flashing light-emitting diode is a special light-emitting device consisting of a CMOS integrated circuit and a light-emitting diode, which can be used for alarm indication and under-voltage and overvoltage indication. When using, the flashing light-emitting diode does not need to be externally connected with other components, so long as the appropriate direct-current working voltage is added at the two-end of the pins to flash and emit light. Voltage-controlled light-emitting diode Ordinary light-emitting diodes belong to current-controlled devices, and the current-limiting resistors with appropriate resistance values should be connected to each other when used. Voltage-controlled light-emitting diode integrates light-emitting diode and a current limiting resistor, which can be connected directly to both ends of the power supply when it is used. Infrared emitting diode  Infrared light-emitting diodes, also known as infrared emitting diodes, are light-emitting devices that can directly convert electrical energy into infrared light (invisible light) and can radiate it out. It is mainly used in various optical control and remote control emission circuits. The structure and principle of infrared light-emitting diodes are similar to those of ordinary light-emitting diodes, but the semiconductor materials used are different. Infrared light-emitting diodes are typically made of gallium arsenide (GaAs), gallium arsenide (GaAlAs), in a fully transparent or light blue, black resin package. VI. LED Trends With the development of the industry, technological breakthroughs, and the application of vigorously promote, LED lighting efficiency is also increasing and the price is constantly lower. The emergence of new combined tube sets also increases the power of a single LED. Through the continuous research and development of the same industry, the breakthrough of new optical design, the development of new lamps, the single product situation is also expected to be further improved. The improvement of control software also makes the use of LED lighting more convenient. LED, known as the fourth generation light source, has the characteristics of energy-saving, environmental protection, safety, long-life, low power-consumption, low heat, high brightness, waterproof, micro, shock proof, easy dimming, beam concentration, easy maintenance, and so on. It can be widely used in all kinds of the pilot light, display, decoration, backlight, general lighting, and other fields. Advantages of LED: high electro-optic conversion efficiency (close to 60%, environmental protection, long life (up to 100000 hours), low working voltage (about 3V), lossless life of repeated switches, small volume, less heat, high brightness, rugged and durable, easy dimming. The color is varied, the beam is concentrated and stable, and the start-up has no delay. Disadvantages of LED: high starting cost, poor color rendering, low efficiency of high power LED, constant current drive (special drive circuit required). In contrast, there are certain defects in traditional lighting. Incandescent lamp: low electro-optic conversion efficiency (about 10%), short life (about 1000 hours), high heating temperature, single-color, and low color temperature. Fluorescent lamps: low electro-optic conversion efficiency (about 30%), harmful to the environment (including mercury and other harmful elements, about 3.5-5mg/pic), non-adjustable brightness (low voltage can not start to glow), ultraviolet radiation, flicker phenomenon, large size, slow start, The increase in the price of the raw materials (the ratio of phosphors to costs increased from 10% to 60%~70%), the repeated switching affects the life. High-voltage gas discharge lamp: large power consumption, unsafe use, short life, heat dissipation problems, mostly used for outdoor lighting. VII. LED Application 1) LED display screen Since the mid-1980s, monochrome and multicolor displays have been introduced, most are text screens or animation screens at first. In the early 1990s, with the development of computer technology and integrated circuit technology, the video technology of LED display screen was realized. TV images can display directly on the screen, especially in the mid-1990s, the blue and green ultra-high brightness LED was successfully developed and put into production rapidly, which greatly expanded the application of outdoor screens with areas ranging from 100m to 300m. At present, LED display screen has been widely used in stadiums, squares, avenues, and even streets and shopping malls. 2) Traffic light Navigation lights have been using LED as a light source for many years, and the present work is to improve and perfect. Road traffic lights have made great progress in recent years, the technology is developing rapidly, and the application is developing rapidly. Its advantages are long life, power-saving and maintenance-free effect are obvious. At present, the peak wavelength of red LED is  630nm, yellow is 590nm and green is 505nm. It should be noted that the driving current should not be too large, otherwise the high temperature in the summer will affect the life of LED. 3) Automobile light Ultra-bright LED can be used as brake lamp, tail lamp, and direction lamp of the automobile, and can also be used in instrument lighting and in-car lighting. It has obvious advantages over an incandescent lamp in vibration resistance, power-saving, and service life. In addition, when it used as a brake light, the response time is 60ns, much shorter than the incandescent (140ms), which increases a safe distance of 4m to 6m on a typical highway. 4) LCD backlight As the backlight of liquid crystal display, LED can not only be used as green, red, blue, white, but also as a color-changing backlight. And many products have entered the production and application stage. 5) Decorative lighting Due to the increase in brightness of light-emitting diodes and the decline in price, coupled with the long life, power saving, easy drive and control than neon lights, and it can not only flash, but also change color during lighting, so it is made of various ultra-high brightness LEDs to decorate the tall buildings, bridges, streets and squares and other landscape in the cities, presenting a colorful, starlight and streamer scene. 6) Lighting source LED lamp has the advantages of anti-vibration, suitable for battery power supply, solid structure, and portability. It will have a great development in special lighting source. As lawn lights, buried lights, microscope field lighting, flashlights, medical lighting, museum or painting exhibition lighting, and reading table lamps. Application of monochromatic LEDs At first, LED was used as the indicator light source of the instrument. Later, various kinds of light-colored LEDs were widely used in traffic signal lights and large-area display screens, resulting in good economic and social benefits.  Automobile signal lamp is also an important field of the LED light source application. Due to the fast response speed (nanosecond level) of the LED, the driver of the trailing vehicle can be informed of the driving condition as soon as possible, thus reducing the occurrence of car rear-end collision accidents. In addition, LED lights in outdoor red, green, blue full-color display, key button miniature flashlight, and other fields have been used. VIII. LED Light Decline Reasons A. Quality issues of LED products 1) LED chip used in the physical condition is not good, and the brightness decay is faster. 2) There are defects in the production process. The heat dissipation of the LED chip can not be well derived from the pins, which leads to the increase of the attenuation of the chip because of the high temperature of the LED chip. B. Applying Problem 1) The LED is a constant current drive, and some of the LEDs are driven by the voltage to cause the LED to decay too fast. 2) The driving current is greater than the rated driving value. Advantages Small size: LED is basically a very small chip encapsulated in epoxy resin because it is very small and light. Low voltage: The power consumption of the LED is quite low, and generally speaking, the operating voltage of the LED is 2~3.6V, that is, only a very weak current is required to light normally. Long service life: The service life of the LED can be up to 100,000 hours under the proper current and voltage. High brightness, low heat: The LED uses cold light-emitting technology, which produces much lower heat than ordinary lighting lamps and lanterns of the same power. Eco-environment: LED is made of non-toxic materials, unlike fluorescent lamps containing mercury will cause pollution, and LED can also be recycled. IX. Complement: Blue LED Blue LED is a blue-emitting LED. In 2014, Yuji Nakamura and Hiro Amano won the Nobel Prize in physics for "inventing high-brightness blue light-emitting diodes, bringing energy-saving and white light sources." The invention of blue LED enables humans to gather together a three-primary colors LED, that emits trichromatic light so that it can produce enough bright white light with LED. The invention of the white LED lamp greatly improves the lighting efficiency of human beings. Principle Two breakthroughs in the late 1980s laid the foundation for the invention of blue LED: one was the development of epitaxial technology of gallium nitride and the another was the doping of P-type semiconductors. Blu LED contains several different (GaN) layers of gallium nitride. The lighting efficiency, adding indium (In) and aluminum (Al) in LED, is greatly improved. Meaning and controversy The invention of the blue LED enabled humans to use LED to produce white light that was bright enough, and the efficiency of the white LED is much higher than that of the incandescent lamp. White LED promotes the invention of all kinds of the LED display screen and also promotes the improvement of lighting efficiency. In particular, the latter makes it possible for humans to reduce carbon emissions and combat climate change. There are also concerns that blue light emitted by blue LEDs could do harm to the human eye because blue light can cause macular degeneration. Related Info: Triacs are at the heart of dimming controls for LED lighting. Triacs used in dimmers have normally been characterised and specified for incandescent lamp loads, which have high current ratings for both steady-state conditions and initial high in-rush currents, as well as very high end-of-life surge current when a filament ruptures. LEDs have much lower steady-state current than incandescents, and their initial turn-on current can be much higher for a few microseconds of each half-cycle of AC line voltage. Therefore, a spike of current can be seen at the beginning of each AC half-cycle. Typically, the current spike for an AC replacement lamp is 6 to 8A peak; the steady-state follow current is less than 100mA. An LED flood lamp for a recessed ceiling fixture designed to replace a typical filament unit that produces 750 lumens consumes only 13W in contrast with the old filament unit, which normally draws 65W. Designing an AC circuit for controlling LED light output is very simple when using the newest triac designs, such as the Littelfuse Q6008LH1LED or Q6012LH1LED Series, because the only components required are a firing/triggering capacitor, a potentiometer, and a voltage breakover triggering device. Two inverse parallel sensitive gate silicon-controlled rectifiers (SCRs), such as the Littelfuse S4X8ES1, can be used as the voltage breakover triggering device, allowing the controlling circuit to produce a wide range of light level outputs. Also, using these components as the triggering device allows achieving a low hysteresis control because two SCRs form a full breakback trigger.  If the application doesn’t demand a wide control range and low hysteresis, a simple variable light control may be designed using quadrac devices, such as the Littelfuse Q6008LTH1LED or Q6012LTH1LED Series (Figure 1). (A quadrac device is a special type of thyristor that combines a diac and a triac in a single package.) The circuit shown in Figure 2 minimises the component count by combining the diac triggering device and an alternistor triac in a single TO- 220 isolated mounting tab package. This control circuit allows a little lower full turn-on voltage due to higher VBO switching of the diac trigger device but offers a light dimming function that operates from 175° to <90° of each AC half-cycle. FAQ 1. What led means? light emitting diode. LED stands for light emitting diode. LED lighting products produce light up to 90% more efficiently than incandescent light bulbs. 2. What is LED used for? Made popular by their efficiency, range of color, and long lifespan, LED lights are ideal for numerous applications including night lighting, art lighting, and outdoor lighting. These lights are also commonly used in electronics and automotive industries, and for signage, along with many other uses. 3. How do LED lights work? An LED bulb produces light by passing the electric current through a semiconducting material—the diode—which then emits photons (light) through the principle of electroluminescence. Don't let that big word scare you! ... In contrast, an incandescent light bulb works by passing electricity through a small wire, or filament. 4. Why is it better to use LED lights? LED is highly energy efficient – Less heat, more light, lower cost. Use less electricity for the same light output - 85% less electricity when compared to conventional lighting and around 18% less electricity compared to CFL. ... LED can make a big impact on your energy use. 5. Why do LEDs fail? Temperatures are too high (or too low).When heat can't dissipate from the heat sink, it can cause lamps to fail prematurely. Also keep the surrounding environment in mind. ... Because LEDs emit light that decreases exponentially as a function of time and temperature. 6. What do LED light colors mean? The lower the color temperature, the warmer the light will appear, or the redder it will appear. The higher the temperature, the cooler the light will appear, or the bluer it will look. 7. What should be the biasing of LED? The LED works when the p-n junction is forward biased i.e., the p- side is connected to the positive terminal and n-side to the negative terminal. 8. Why are LED lights used mainly for lighting nowadays? Additionally, unlike Compact Fluorescent Lights (CFLs), LED lights do not contain mercury that can spill if dropped, making them a safer choice for household use. LEDs, which stand for Light Emitting Diodes, burn light 90 percent more efficiently than incandescent bulbs. 9. What are the disadvantages of LEDs? High up-front costs. Transformer compatibility. Potential color shift over lamp life. Performance standardization has not yet been streamlined. Overheating can cause reduced lamp life. 10. Why do my LED lights burn out so fast? The most common reasons for LED blowing out are high voltage, bad contacts, use of incompatible dimmer switch, or recessed lighting. Other causes include overheating due to not using the right fixtures, or simply a bad batch of lightbulbs! You May Also Like: Design LED strips on My House Walls Product Recommendation: LTL-4251NHBP LM3080N VC1510145UY3