Surely in our time there are no such people who have never encountered LEDs. After all, now they are everywhere - they are used for simple flashlights, and for home lighting lamps, and for lampposts on the streets, and for cars, and even for backlit kettles. And this is not surprising, because at the moment there is no more environmentally friendly and energy-saving, and besides, such a compact type of lighting fixtures does not exist.
Of course, almost everyone has seen the glow of a working LED component and knows what an LED is, but many even have no idea how this lighting element works. But such knowledge can be useful, and therefore it makes sense to try to explain the device of the LED and the principle of its operation, to talk about the types and modifications that exist in our time.
In general, the beginning of these compact light elements was laid in the middle of the last century and they were used only to indicate the backlight in various devices, since their light was not very bright, one might even say dim. However, everything changed at the end of the 20th century with the advent of the blue light diode, and after that bright elements of this type of green, yellow and white appeared.
The LED is a miniature lighting device in a molded plastic housing in various colors with two or more contacts based on a crystal. Today it is a fairly common type of lighting.
Someone may say that it’s not worth getting into this jungle, that it’s all very difficult, but in fact, LEDs are simple, like everything ingenious, and it’s not difficult to understand how an LED works. So let's get started.
Classification of LEDs
LEDs are classified according to many characteristics, but the main one is a small technological difference in the device, which is caused by a difference in electrical parameters, as well as the area of \u200b\u200buse of the lighting device on crystals. And what the LED consists of can be seen in the picture above.
There are several designs of LEDs, depending on how it is arranged.
DIP
It has a body in the form of a cylinder with two contacts. This is the first of the invented LEDs. Its epoxy shell itself, rounded at the top, works like a lens, directing the light flux in the right direction. Output contacts are recessed with legs into special holes of the printed circuit board and soldered. The emitter itself is located on the cathode, which has the shape of a flag and is connected to the anode with a thin wire.
Various modifications can have two or three crystals of different colors, combined in one case with two to four leads. In addition, some can be equipped with a built-in microcontroller that controls the switching modes or sets the flickering time of the crystals.
Such DIP elements are low current. They are used mainly as indicators or as light elements of garlands.
DIP LED Of course, like any device, they tried to improve it in order to increase the luminous flux, as a result of which a more high-tech LED was produced in the same four-pin package. This design of the LED was called "piranha".
But the increased luminous flux naturally led to an increase in the element and to heating of the crystals, as a result of which the "piranha" was not widely used. Well, when SMD components with a different structure appeared on the radio electronics market, the point in producing such LEDs completely disappeared.
smd
This component on crystals differs from the previous one primarily in that it is mounted directly on the surface of the printed circuit board. In fact, his invention made a breakthrough in this field. And if, when mounting DIP LEDs, it was possible to mount elements only on one side of the board, since the conductive tracks were on the other, then with the advent of SMD components, it became possible to mount double-sided printed circuit boards.
This, coupled with the smaller dimensions of the elements, made it possible to significantly reduce the size of devices based on them and fully automate the process of assembling printed circuit boards.
To date, such LEDs are the most popular and are used for the manufacture of various lighting devices. The base of the SMD-LED case, on top of which the crystal is fixed, also serves as a heatsink for it. In addition, the phosphor layer between the lens and the semiconductor (which determines the color of the LED) can have a different composition and can neutralize ultraviolet radiation.
SMD LED There are also SMD LEDs that do not have a lens. Such an element is produced in the form of a rectangle or square and has a wider radiation angle.
SOV (Chip-On-Board)
The decoding of the name of this component in translation from English sounds like “a chip on a board”. The latest development, which, most likely, will very soon become the leader among LEDs in creating artificial lighting.
Similar components differ in that not one, but many crystals that do not have cases are fixed on an aluminum base (substrate) by means of dielectric glue, and then the finished matrix is completely covered with a phosphor.
As a result, the LED thus obtained evenly distributes the light flux, eliminating shadow formation.
There is another type of COB LEDs - these are components created using COG technology (Chip-On-Glass, which means “chip on glass”). The crystals here are placed not on an aluminum substrate, but on a glass one. Just on the basis of LEDs created using this technology, it became possible to produce well-known filament lamps that operate on a 220-volt network. The emitter in them is a glass rod with crystals, on which a layer of phosphor is applied.
COB LED The principle of operation of the LED
Regardless of the described technical classifications, the principle of operation of all LEDs without exception is based on a radiating element. The crystal, which is inherently a semiconductor having various types of conductivity, converts electric current into a glow. An N-conductive material is obtained by doping with electrons, while a p-conductive material is obtained with holes. As a result, new charge carriers with the opposite direction are created.
As a result, when a forward voltage is applied, electrons, like holes, begin to move towards the p-n junction. When charged particles overcome the barrier, their recombination begins. As a result, this creates the possibility of the passage of electric current. Well, in the process of recombination, electrons and holes already release photons.
The application of such a physical phenomenon applies to all elements that fall under the definition of a semiconductor diode. The problem is that the limits of the visible spectrum of radiation are located closer than the length of photons. For this reason, scientists have done a lot of work to streamline the movement of particles, forcing them to move in the range from 400 to 700 nm.
But on the other hand, after all the experiments carried out, several new compounds appeared, such as gallium arsenide and gallium phosphide, and, of course, their more complex forms that have different wavelengths, i.e., the color of the radiation.
Of course, with such work on the release of light, heat should also be generated, although in small quantities, because no one has repealed the laws of physics. For this reason (after all, heating reduces the performance of semiconductors), when installing high-power LEDs, it becomes necessary to cool, which requires a radiator. The role of such a cooling element in the SOW, for example, is played by the aluminum base on which the crystals are located.
Emission spectra
Modern LEDs have six main spectra, i.e. their glow can be yellow, green, red, blue, cyan and white. And the most difficult for scientists was the creation of a blue light element on crystals.
In general, the frequency of radiation emitted by LEDs lies in a narrow direction. Based on all the data, it can be called monochrome. And of course, that it has a fundamental difference from the frequency of solar radiation or incandescent lamps.
For several years now, there have been disputes about the effect of such radiation on human vision, as well as on the whole organism as a whole. But the problem is that all such discussions so far have not led to anything, because there is not a single documentary evidence of research in this area.
Advantages
If we consider the advantages of LEDs, then there will be a very significant number of them.
First, they are very economical in terms of energy consumption. To date, there are no lighting devices that could compete with them in this parameter. Moreover, this does not affect the strength of the light flux emitted by the elements on the crystals.
The service life of such LED components can also be attributed to profitability, since the frequent purchase of lighting devices negatively affects the financial condition. If you look at the statistics, you have to buy LED lamps 10 times less often than fluorescent ones, and incandescent bulbs generally change 35-40 times more often. At the same time, the power consumption when using LEDs is 87% lower in comparison with the "Ilyich's light bulb"!
Secondly, LED lamps are convenient and easy to connect and do not require any special skills. In addition, for example, in the same billboards, if several elements fail, nothing terrible will happen. It will not affect his work in any way. Well, with a huge service life of LEDs, the problem of replacing them is also solved. And the main convenience is that such elements can work at almost any temperature.
Thirdly, it is, of course, their reliability. After all, in order to split an incandescent lamp or a fluorescent tube, you do not need to make special efforts. But with the LED you have to tinker. The epoxy body does not split so easily.
It is impossible to ignore the aesthetic side of this issue, because the possibility of playing with color when using these light sources is practically unlimited, except for the imagination and fantasy of a person. Working with LEDs can be compared to the art of painting by an artist on his canvases.
And therefore, despite the fact that in our time, sales of such lighting elements are not too impressive yet, most likely, very little time will pass, and LEDs will come out on top in this indicator, displacing other types of lighting from the shelves of electrical stores.
Since the discovery of monochrome red LEDs in 1962, the active development of semiconductor light sources has begun.
The discovery of blue and white diodes took the technology to a new level.
Since then, the device of the LED, its characteristics and design has been constantly changing. Now they are widely used in lighting engineering, electronics and other fields.
An LED is a semiconductor device that emits light when an electric current is passed through it. What an LED consists of: a crystal enclosed in a protective case with leads. The crystal is placed on a non-conductive substrate and emits a certain color. To obtain the desired glow, chemical compositions from various semiconductors and phosphors are used.
A crystal consists of two or more semiconductors of different types of conductivity. The principle of operation of the LED is as follows - in the forward direction, an electric current is passed through it. In the electron-hole transition at the boundary of two substances, the movement of electrons and holes occurs, as a result of which energy is released in the form of a quantum of light and the device begins to shine.
Advantages:
- high light output;
- high mechanical strength and vibration resistance;
- long term of work;
- small heating;
- the period of operation does not depend on the number of on-off cycles;
- different range of white LEDs - from 2700 K to 6500 K;
- spectral purity obtained due to the principle of the device;
- there is no turn-on delay;
- wide range of radiation angles (from 15 degrees to 180 degrees);
- electrical safety, as high voltages are not required;
- lack of sensitivity to low temperatures;
- reliability;
- variety of forms;
- profitability;
- environmental friendliness, due to the absence of mercury in the design of the LED and other harmful components in the composition of the light emitting diode.
Flaws:
- work at high temperatures should not be allowed - the crystal begins to degrade;
- high cost of the finished product.
Application:
- street, home and industrial lighting;
- indication;
- street advertising, running lines;
- lights and traffic lights;
- backlighting of telephone, TV, computer and other liquid crystal displays;
- toys, badges and other entertainment elements;
- diode road signs;
- light cords Duralight;
- in phytolamps.
The lighting device based on LEDs consists of:
- emitting diode;
- drivers;
- plinth;
- corps.
Among the major manufacturers of LEDs, the Japanese company Nichia Corporation and its division Nichia Chemical can be distinguished. They are leaders in the manufacture of super-bright blue, white and green diodes. Also, Phillips, Cree, Seoul Semiconduction are engaged in the manufacture of emitting diodes from Russian companies, Optogan and Svetlana-Optoelectronics can be distinguished.
Nichia Chemical pioneered the development of a white and blue LED.
How LEDs of different types are arranged and how they differ
LEDs can be classified according to different criteria. The main difference is in technology and electrical parameters.
DIP
The abbreviation DIP comes from the words Direct In-line Package. Such LEDs have been known since the end of the last century. The device is a glass or plastic transparent flask 3 or 5 mm in size, which contains a semiconductor crystal. The bulb is a lens and forms a directed beam of light. The crystal is fixed on the cathode, which is connected with the help of a wire to the anode. Contacts in the form of metal legs come out of the case, through which the LED is connected to the circuit.
Compared to conventional incandescent lamps, the device of an LED lamp is technically more complicated. If a transparent glass case is used for the former, then in the case of the latter, it will not be possible to see anything inside. In order to find out what such a light source consists of, it is necessary to disassemble it into parts.
The general arrangement of LED light bulbs, regardless of manufacturer, is almost identical (with minor differences). The range of standard products with E14 or E27 base is divided into three categories - branded, low-grade Chinese and filament.
low quality chinese light bulbs
When parsing a branded lamp, you can find all the structural elements necessary for reliability and durability. But if you look under the case of a cheap Chinese product, then the first thing you will not find is a heatsink and a driver.
The driver is usually replaced with a power supply with a non-polar capacitor that is unable to stabilize the output current. Install such a block in the center of the board with diodes. If you look at it from above, you can see a diode bridge with resistors, from below - two capacitors. This allows you to significantly reduce the cost and quality of the product.
To cool the device, small holes are made in the case. The efficiency is low, the crystals burn out very quickly. The board is mounted on a plastic case and secured with latches. Two soldered wires are used to connect to the base.
Filament lamps
The filament light source looks like an incandescent lamp, but structurally remains an LED product. In this case, there is no need for heat removal, but the use of devices in the domestic sphere is associated with purely aesthetic considerations.
The main element of the filament device is the LED filament. Depending on the number of such threads, products of different capacities are produced. A filament is a thin glass rod with SMD diodes on its surface. The upper part is covered with a phosphor, giving a yellow tint. To remove heat, a glass flask is used, the inside of which is filled with gas.
Due to the lack of space for the driver inside, manufacturers place a low-quality power module. This increases the pulsation, which negatively affects the visual organs. To get rid of flickering, a plastic ring with a high-quality driver is added between the base and the bulb.
The principle of operation of LED lamps
The principle of operation of these devices is based on complex physical processes. When an electric current is applied, two substances made of different materials come into contact. This leads to the formation of a luminous flux.
The paradox of the system is due to the fact that none of the materials used to make the two substances is a conductor of electric current. These are semiconductors that can only pass current in one direction. Therefore, when connecting LEDs, it is important to observe the polarity. One material is endowed with negative electrons, and the other with positive ions.
Other processes are also activated in semiconductors. At the moment of change of state, thermal energy is released. Using an experimental method, the inventors found the right combination of substances, in which, in addition to energy, light radiation also appears.
All devices that pass current in one direction are called diodes. LEDs are diodes capable of emitting a luminous flux.
The first LED diodes emitted light in a narrow spectrum - red, yellow or green. At the same time, the luminescence intensity was minimal. For a long time, LEDs were used exclusively as indicators. Today, the radiation range has been significantly expanded and covers almost the entire spectrum. On the other hand, certain wavelengths are always longer, so these devices are divided into cold and warm light sources (depending on the thermal temperature).
Assembly methods
According to the method of assembly, the products are divided into several categories.
DIP
DIP stands for Dual In-line Package. The design of the devices is interesting, but significantly outdated. The following sizes of LEDs are distinguished:
- 1.0 cm.
Also, semiconductor products differ in color, material of manufacture, chip shape. Among the advantages of the DIP assembly, we highlight low heating and high brightness. There are single-color and multi-color (RGB-technology). Recognizable by its characteristic cylindrical shape and built-in convex type lens.
"Piranha"
This group of lighting devices is characterized by a high luminous flux. They are made in a rectangular shape, have four PIN-pins, are red, blue, white or green.
Compared to DIP technology, the products sit more rigidly and firmly on the board. The lead substrate increases thermal conductivity, but at the same time reduces the overall safety during operation. Widespread due to a large range of operating temperatures.
SMD technology
SMD stands for Surface Mounting Device (translated from English - "device fixed on the surface"). These LEDs are characterized by a power in the range of 0.01-0.2 W. The main feature is associated with the presence of several crystals (1–3) mounted on a ceramic substrate.
The case is covered with a phosphor. Standard solder is used to connect the main board and pads.
Among the shortcomings, we single out low maintainability: if at least one diode fails, then the whole board will have to be replaced.
COB technology
The latest and most reliable LED manufacturing technology is called Chip On Board (COB). Semiconductors are mounted on a board without a case and any substrate, after which they are coated with a phosphor.
The main advantage is associated with a small glow area at high power. The uniform glow of the product is guaranteed by the high density of LEDs and the presence of a phosphor. Such LEDs are more commonly used today.
Device of LED light sources
The LED source consists of the following structural elements:
- LED diodes;
- drivers;
- frame;
- radiator;
- plinth.
LEDs
A few years ago, the design of the LED lamp was slightly different due to the lack of a wide range of LED diodes. The most common were 3–5 mm chips. Later, 10 mm products appeared.
There are many more LEDs today. The most commonly used are SMD 5050, SMD 3528, SMD 5730, SMD 2835, 1W, 3W and 5W.
The number of LEDs is different, it is set by the manufacturer. When mounting several diodes, special calculations are made to derive the optimal current consumption. Solder is carried out to textolite or aluminum boards. LEDs are assembled in groups connected in series. Again, the number of groups is unlimited.
A serial connection provides constant current, but there is a significant drawback - if at least one LED diode fails, the entire product stops working. On the other hand, the diode can be easily replaced with a new one.
The boards to which light sources are soldered are classified according to their shape and are round, rectangular, oval, polygonal, etc.
Drivers
Drivers are designed to convert the incoming voltage to a value suitable for powering the device. Moreover, the power supply for each group of LEDs can be different. The most common are transformer circuits with drivers.
Structural elements can be of two types - open and closed (in the case). Mount them in the body of lamps, lighting fixtures.
Cheap drivers are used in conventional flashlights, in which the LEDs are powered by batteries. In this case, there is no need for a current limiting resistor. Because of this, the diodes can receive increased current, which leads to their rapid failure.
Chinese manufacturers often try to save on devices by installing conventional current limiters with a capacitor-based circuit instead of drivers. Avoid buying such products, because in addition to being extremely uneconomical, they have a negative impact on human health (high pulsation).
plinth
Since LED products are positioned as the best analogues of incandescent lamps, it is not surprising that they are made with standard socles - E27 and E14. The latter are often used in night and wall lamps.
There are different standards abroad, so you can often find E26 LED lamps there.
Frame
Unlike incandescent lamps, for LED lamps there is no need for complete tightness of the flasks, and there is no gas medium inside. One of the varieties of LED lamps is a filament source, which repeats the structure of an incandescent lamp and needs a gaseous medium.
Consuming the same amount of electricity, the products shine much brighter than their counterparts. A conventional LED lamp has a closed bulb made of glass or plastic. A matte finish reduces light transmission, but this is a negligible production cost.
Radiators
These electrical products are afraid of high temperature and overheating. For this reason, a heat dissipation device is necessary to increase the service life. Aluminum boards partially reduce the effect of overheating, but this is not enough. Expensive and high-quality lamps necessarily use radiators, the size of which depends on the number of LEDs in the device.
The presence of a radiator increases the cost and dimensions of the product, but is a prerequisite for creating a high-quality and durable device.
The layout of the components
Depending on the manufacturer, the device and design of the lamp is different. On the other hand, the general layout principle remains the same. The assembly begins with a base, where a driver, a radiator, a board with LED diodes and a flask are installed in series.
For comparison, consider the device of a product from two manufacturers.
BBK LED Bulb
The plinth is made of plastic. A quality driver is installed inside. Aluminum is used for the case, which acts as a radiator. A board with diodes and a lens are attached there. The presence of this lens reduces the light output of the device.
Gauss lamp
Again, the base is made of plastic, there is a driver and an aluminum case with a diode board installed. The design guarantees the durability of the product.
How to check the LED lamp when buying
Pick up the LED lamp and inspect it externally to make sure there are no flaws. This can be done only if a transparent flask is used. First, check the radiator (it is available as a cast or stacked type). The higher the power of the product, the larger the radiator should be. An excellent option would be the use of aluminum or ceramic coolers.
Ideally, the electrical element should be coated with thermoplastic. Make sure that there are no backlashes and mechanical defects in the base. Also in any store it is possible to connect the lamp to the electrical network to check its performance. Having done this, take a look at the emitted light. Use the camera on your smartphone to ensure there is no flicker or flicker. Never buy a lamp that flickers when working.
The information obtained on the device and the principle of operation of the LED lamp may not be enough to select a high-quality lighting device that is characterized by safety, reliability and durability. You also need to take into account other criteria, including characteristics and manufacturer, which are described in detail.
The device and principle of operation of LED lamps. The main parts of the lighting device:
LEDs;
- driver;
- plinth;
- frame.
The principle of its operation completely repeats the processes occurring in an ordinary semiconductor diode with a p-n junction made of silicon or germanium: when a positive potential is applied to the anode, and a negative one to the cathode, the movement of negatively charged electrons to the anode begins in the materials, and holes to the cathode. As a result, the diode passes electric current in only one direct direction.
However, the LED is made of other semiconductor materials, which, when bombarded in the forward direction by charge carriers (electrons and holes), carry out their recombination with transfer to another energy level. As a result, photons are released - elementary particles of electromagnetic radiation in the light range.
Even in electrical circuits, the designations of ordinary diodes are used as their designations, only with the addition of two arrows indicating the emission of light.
Semiconductor materials have different photon emission properties. Substances such as gallium arsenide (GaAs) and gallium nitride (GaN), being direct-gap semiconductors, are simultaneously transparent to the visible spectrum of light waves. When they replace p-n junction layers, light is released.
The layout of the layers used in the LED is shown in the figure below. Their small thickness of the order of 10÷15 nm (nanomicrons) is created by special methods of chemical vapor deposition. The layers contain contact pads for the anode and cathode.
As with any physical process, during the conversion of electrons into photons, there are energy losses due to the following reasons:
Part of the light particles is simply lost inside even such a thin layer;
- when leaving the semiconductor, optical refraction of light waves occurs at the crystal/air interfaces, distorting the wavelength.
The use of special measures, such as the use of a sapphire substrate, makes it possible to create a greater luminous flux. Such designs are used for installation in lighting lamps, but not for conventional LEDs used as indicators, shown in the figure below.
They have a lens made of epoxy resin and a reflector to guide the light. Depending on the purpose, the light can propagate in a wide angle range of 5-160°.
Expensive LEDs produced for lighting lamps are manufactured by manufacturers with a Lambert diagram. This means that their brightness is constant in space and does not depend on the direction of radiation and the angle of observation.
The dimensions of the crystal are very small and a small amount of light can be obtained from one source. Therefore, for lighting lamps, such LEDs are combined in fairly large groups. At the same time, it is very problematic to create uniform illumination from them in all directions: each LED is a point source.
The frequency spectrum of light waves from semiconductor materials is much narrower than from ordinary incandescent lamps or the sun, which tires the eyes of a person, creates a certain discomfort. In order to correct this shortcoming, a phosphor layer is introduced into individual LED designs for illumination.
The magnitude of the emitted light flux of semiconductor materials depends on the current passing through the p-n junction. The greater the current, the higher the radiation, but up to a certain value.
Small dimensions, as a rule, do not allow the use of currents exceeding 20 milliamps for indicator structures. Powerful lighting lamps use heat dissipation and additional protection measures, the use of which, however, is strictly limited.
At start-up, the luminous flux of the lamp increases proportionally with increasing current, but then, due to the formation of heat losses, it begins to decrease. It should be understood that the process of emitting photons from the conductor is not associated with thermal energy, LEDs are cold light sources.
However, the current passing through the LED at the points of contact between the various layers and electrodes overcomes the contact resistance of these sections, which causes heating of the materials. The generated heat initially only creates energy losses, but as the current increases, it can damage the structure.
The number of LED crystals installed in one lamp can exceed a hundred working elements. For each of them it is necessary to bring the optimal current. For this, fiberglass boards with conductive paths are created. They can have a variety of designs.
LED crystals are soldered to the contact pads of the boards. Most often they are formed into certain groups and fed in series with each other. The same current is passed through each created chain.
Such a scheme is technically easier to implement, but it has one main drawback - if any one contact is broken, the entire group stops shining, which is the main cause of lamp failure.
Drivers. The supply of constant voltage to each group of LEDs is carried out from a special device, which was previously called a power supply, and now the term “driver”.
This device has the functions of converting the input voltage of the network, for example, ~ 220 Volts of the apartment or 12 Volts of the car network into the optimal power supply for each series group.
The supply of one stabilized current to each crystal in a parallel circuit is technically difficult and is used in rare cases. The driver can work on the basis of a transformer or other circuit. Among them are the following options. Depending on the configuration and the number of applied elements, they may be different:
The simplest and cheapest drivers are powered by a stabilized voltage, the network of which is protected from surges and surges. They may even lack a current-limiting resistor in the output power circuit, which is typical for rechargeable flashlights, the LEDs of which are often connected directly to the battery output.
As a result, it turns out that they are powered by an overestimated current, and although they shine quite brightly, they burn out very often. When using cheap lamps with drivers without surge protection of the lighting network, the LEDs also often burn out without having worked out the declared resource.
Well-designed power supplies generate little to no heat during operation, and cheap or overloaded drivers use some of their electricity to heat up. Moreover, such useless losses of electric power can be comparable, and in some cases exceed the energy spent on the release of photons.
In incandescent lamps, light is obtained from a white-hot tungsten filament, in fact - from heat. Like hot coals in a furnace heated by the thermal action of an electric current, when the electrons oscillate quickly and quickly and collide with the nodes of the crystal lattice of the conductive metal, they emit visible light, which accounts for, however, only less than 15% of the total electrical energy consumed that feeds the lamp .
LEDs, unlike incandescent lamps, emit light not at all due to heat, but due to the peculiarity of their design, which is fundamentally aimed at ensuring that the energy of the current goes precisely to emit light, and of a certain wavelength. As a result, the efficiency of the LED as a light source exceeds 50%.
The current passes here, while at the transition there is a recombination of electrons and holes with the emission of photons (quanta) of visible light with a certain frequency, and therefore with a certain color.
Any LED is fundamentally arranged as follows. First, as noted above, there is an electron-hole junction here, consisting of p-type semiconductors (main current carriers are holes) and n-type semiconductors (main current carriers are electrons) in contact with each other.
When a current is passed through this transition in the forward direction, then at the point of contact of semiconductors of two opposite types, a charge transition occurs (charge carriers jump between energy levels) from a region with one type of conductivity to a region with another type of conductivity.
In this case, electrons with their negative charge are combined with ions of positively charged holes. At this moment, photons of light are born, the frequency of which is proportional to the difference in the energy levels of atoms (the height of the potential barrier) between the substances on both sides of the transition.
Structurally, LEDs come in various forms. The simplest form is a five-millimeter body - a lens. Such LEDs can often be found as indicator lights on various household appliances.From above, the LED housing has the shape of a lens. A parabolic reflector (reflector) is installed at the bottom inside the housing.
On the reflector is a crystal that emits light at the point where the current passes through the p-n junction. From the cathode - to the anode, from the reflector - towards the thin wire, the electrons move through the cube - the crystal.
This semiconductor crystal is the main element of the LED. Here it has a size of 0.3 by 0.3 by 0.25 mm. The crystal is connected to the anode with a thin wire jumper. The polymer housing is simultaneously a transparent lens that focuses light in a certain direction, thus obtaining a limited angle of divergence of the light beam.
To date, LEDs are available in all colors of the rainbow, ranging from ultraviolet and white, ending with red and infrared. The most common are red, orange, yellow, green, blue and white LEDs. And the color of the glow here is by no means determined by the color of the case!
The color depends on the wavelength of the photons emitted at the p-n junction. For example, the red color of a red LED has a characteristic wavelength of 610 to 760 nm. The wavelength, in turn, depends on the material that was used in the production of a particular LED. So, to obtain a color from red to yellow, impurities of aluminum, indium, gallium and phosphorus are used.
To obtain colors from green to blue - nitrogen, gallium, indium. To obtain a white color, a special phosphor is added to the crystal, which converts the blue color to white using.