Semiconductor LED. LEDs with phosphor. How to calculate resistance for an LED

Problem solving
Introduction

LED, or light emitting diode (LED, LED, LED from English “ Light-emitting diode ”) Is a semiconductor device with an electron-hole junction (pn-junction) or a metal-conductor contact, which creates optical radiation when an electric current passes through it in the forward direction. An LED crystal produces optical radiation in a rather narrow spectrum. Its spectral characteristics depend primarily on the chemical composition of the semiconductors used in its manufacture. In other words, an LED crystal emits a specific color (if we are talking about LEDs in the visible range), in contrast to a lamp emitting a wider spectrum, and where a specific color is eliminated by an external light filter.

History

Electroluminescence was first discovered and described in 1907 by the scientist Henry Joseph Round, who discovered it while studying the passage of current in a pair of metal - silicon carbide (carborundum, SiC), and noted the yellow, green and orange glow on the cathode.

These experiments were later, independently of the Round, repeated by O.V. Losev in 1923, who, while experimenting with a rectifying contact from a pair of carborundum - steel wire, found a weak glow at the contact point of two dissimilar materials - electroluminescence of a semiconductor transition (at that time, the concept "Semiconductor junction" did not exist yet). This observation was published, but then the weighty significance of this observation was not understood and therefore not investigated for many decades.

Probably the first LED to emit light in the visible spectrum was made in 1962 at the University of Illinois (USA) by a group led by Nick Holonyak.

Diodes made from indirect-gap semiconductors (for example, silicon, germanium, or silicon carbide) practically do not emit light. However, in connection with the development of silicon technology, work is actively underway to create silicon-based LEDs. The Soviet yellow LED KL 101 based on silicon carbide was produced back in the 70s, but had a very low brightness. IN recent times great hopes are associated with the technology of quantum dots and photonic crystals.

What is the difference?

LED light emitting technology is fundamentally different from traditional light source technology such as incandescent, fluorescent and discharge lamps high pressure... The LED has no gas, no filament, and does not have a fragile glass bulb or potentially unreliable moving parts.

The main difference between LED light sources and traditional ones is that LEDs use a completely different principle of light generation and use completely different materials. A less obvious difference is that the LED light fixture erases the boundary between lamp and luminaire. In LED lighting technology, "lamps", which are LEDs, are inseparable from a "lamp", namely: housing, electronics and lenses.

LED characteristics

The current-voltage characteristic of LEDs in the forward direction is non-linear. The diode begins to conduct current, starting at a certain threshold voltage. This voltage makes it possible to accurately determine the semiconductor material.

Modern super-bright LEDs have less pronounced semiconduction than conventional diodes. High-frequency pulsations in the supply circuit (so-called “needles”) and reverse voltage surges lead to accelerated degradation of the crystal. The rate of degradation also depends on the supply current (non-linear) and the temperature of the crystal (non-linear).

The cost

The cost of high-power LEDs used in portable floodlights and car headlights is quite high today - about $ 8-10 or more per piece. As a rule, several dozen not very powerful LEDs are used in small flashlights and household lamps-assemblies.

By the beginning of 2011, the cost of high-power (1 W or more) LEDs has dropped and starts at $ 0.9. The cost of super-powerful (10W and more P7 and CREE M-CE 15-20 $ CREE XM-L 10W 1000Lm) is about $ 10.


Benefits

Compared to other electrical light sources (converters of electricity into electromagnetic radiation visible range), the LEDs have the following differences:

    High luminous efficacy. Modern LEDs are on par with sodium discharge lamps and metal halide lamps, reaching 150 lumens per watt;

    High mechanical strength, vibration resistance (no filament and other sensitive components);

    Long service life - from 30,000 to 100,000 hours (when working 8 hours a day - 34 years). But it is not infinite either - with prolonged operation and / or poor cooling, the crystal becomes "poisoned" and the brightness gradually drops;

    The spectrum of modern LEDs varies. - from warm white (2700 K) to cold white (6500 K);

    Small inertia - turn on immediately at full brightness, while for mercury-phosphorus (fluorescent-economical) lamps the turn-on time is from 1 sec to 1 min, and the brightness increases from 30% to 100% in 3-10 minutes, depending on the ambient temperature Wednesday;

    Number of on-off cycles do not significantly affect the service life of LEDs (in contrast to traditional light sources - incandescent lamps, gas-discharge lamps);

    Different angle of radiation - from 15 to 180 degrees;

    Low cost indicator LEDsbut relatively high cost when used in lighting, which decreases with increasing production and sales (economies of scale);

    Safety - no need for high voltage;

    Insensitive to low and very low temperatures... However, high temperatures are contraindicated for an LED, like any semiconductor;

    Sustainability - absence of mercury, phosphorus and ultraviolet radiation, unlike fluorescent lamps.

Application of LEDs

    In street, industrial, household lighting (including LED strip);

    As indicators - both in the form of single LEDs (for example, a power-on indicator on the instrument panel), and in the form of a digital or alphanumeric display (for example, numbers on a clock);

    The array of LEDs is used in large outdoor screens, in creeping lines. Such arrays are often referred to as LED clusters, or simply clusters;

    In optocouplers;

    High-power LEDs are used as light sources in street lamps and traffic lights;

    LEDs are used as sources of modulated optical radiation (signal transmission via optical fiber, remote controls, Internet);

    In the backlight of LCD screens (mobile phones, monitors, TVs, etc.);

    In games, toys, icons, USB devices and more;

    In LED road signs;

    In flexible PVC light cords Duralight.


If after reading this article you still have questions about lED equipment, then we will be happy to help you choose the lamp that is right for you!

1. What is the LED made of?From a semiconductor crystal on a substrate, a package with contact pins and an optical system. Modern LEDs bear little resemblance to the first box-type LEDs used for indication. The construction of a high-power LED is shown schematically in the figure. 2. How does the LED work?The glow arises from the recombination of electrons and holes in the pn junction region. So, first of all, a p-n junction is needed, that is, the contact of two semiconductors with different types of conductivity. To do this, the near-contact layers of a semiconductor crystal are doped with different impurities: acceptor on one side, donor on the other, but not every pn junction emits light. Why? Firstly, the band gap in the active region of the LED should be close to the energy of quanta of light in the visible range. Secondly, the radiation probability during recombination of electron-hole pairs should be high, for which the semiconductor crystal should contain few defects, due to for which recombination occurs without radiation. These conditions, to one degree or another, contradict each other. In reality, in order to meet both conditions, one pn-junction in the crystal is not enough, and it is necessary to produce multilayer semiconductor structures, the so-called heterostructures, for the study of which the Russian physicist Academician Zhores Alferov received the 2000 Nobel Prize. 3. Does this mean that the more current flows through the LED, the brighter it shines?Of course, yes. After all, the greater the current, the more electrons and holes enter the recombination zone per unit time. But the current cannot be increased indefinitely. Due to the internal resistance of the semiconductor and the pn junction, the diode will overheat and fail. 4. Why is LED good?In an LED, unlike an incandescent lamp or fluorescent lamp, electricity is converted directly into light radiation, and in theory this can be done with almost no loss. Indeed, the LED (with proper heat dissipation) heats up little, which makes it indispensable for some applications. Further, the LED emits in a narrow part of the spectrum, its color is clear, which is especially appreciated by designers, and UV and IR radiation are usually absent. The LED is mechanically strong and extremely reliable, its service life reaches 100 thousand hours, which is almost 100 times more than an incandescent light bulb, and 5 to 10 times more than a fluorescent lamp. Finally, an LED is a low-voltage electrical device, and therefore, safe. 5. When did LEDs begin to be used for lighting?Initially, LEDs were used exclusively for indication. To make them suitable for lighting, it was necessary first of all to learn how to make white LEDs, as well as to increase their brightness, or rather luminous efficiency, that is, the ratio of luminous flux to energy consumption. In the 60s and 70s, LEDs based on phosphide were created. and gallium arsenide, emitting in the yellow-green, yellow and red regions of the spectrum. They were used in indicator lights, scoreboards, dashboards of cars and airplanes, advertising screens, different systems visualization of information. In terms of light output, LEDs have outperformed conventional incandescent lamps. They also surpassed them in terms of durability, reliability, safety. One thing was bad - there were no blue, blue-green and white LEDs. By the end of the 80s, more than 100 million LEDs were produced in the USSR a year, and the world production was several tens of billions. 6. What does the LED color depend on?Exclusively from the band gap in which electrons and holes recombine, that is, from the semiconductor material, and from dopants. The “blue” the LED, the higher the energy of the quanta, which means that the larger the band gap must be. 7. What is LED quantum output?Quantum yield is the number of emitted light quanta per recombined electron-hole pair. Distinguish between internal and external quantum efficiency. Internal - in the pn-junction itself, external - for the device as a whole (after all, light can be lost "along the way" - absorbed, scattered). The internal quantum efficiency for good crystals with good heat dissipation reaches almost 100%, The external quantum efficiency record for red LEDs is 55%, and for blue LEDs it is 35%. External quantum efficiency is one of the main characteristics of LED efficiency. 8. How to get white light using LEDs?There are three ways to get white light from LEDs, the first is by mixing colors using RGB technology. One matrix densely accommodates red, blue and green LEDs, the radiation of which is mixed using an optical system, such as a lens. The result is white light. The second method consists in the fact that three phosphors emitting blue, green and red light, respectively, are applied to the surface of an LED emitting in the ultraviolet range (there are some). This is similar to how a fluorescent lamp shines. And finally, in the third method, yellow-green or green plus red phosphor is applied to a blue LED, so that two or three radiations are mixed to form white or near-white light. 9. Which of the three is the best way?Each method has its own advantages and disadvantages. RGB technology, in principle, allows not only to obtain white color, but also to move along the color chart when the current through different LEDs changes. This process can be controlled manually or by means of a program, it is also possible to obtain different color temperatures. Therefore, RGB matrices are widely used in dynamic lighting systems. In addition, a large number of LEDs in the matrix provide a high total luminous flux and high axial luminous intensity. But the light spot due to the aberrations of the optical system has an uneven color in the center and at the edges, and most importantly, due to uneven heat removal from the edges of the matrix and from its middle, the LEDs heat up differently, and, accordingly, their color changes differently. in the process of aging - the total color temperature and color "float" during the operation. This unpleasant phenomenon is difficult and expensive to compensate for. White LEDs with phosphors are significantly cheaper than RGB LED matrices (per unit of luminous flux), and allow you to get good white color. And for them, in principle, it is not a problem to get to a point with coordinates (0.33, 0.33) on the MCO color diagram. The disadvantages are as follows: first, they have less light output than RGB matrices because of the transformation of light in the phosphor layer; secondly, it is rather difficult to accurately control the uniformity of the phosphor deposition in technological process and therefore the color temperature; and finally thirdly - the phosphor also ages, and faster than the LED itself. The industry produces both LEDs with a phosphor and RGB matrices - they have different areas of application. 10. What are the electrical and optical characteristics of LEDs?The LED is a low voltage device. A typical LED used for indication consumes from 2 to 4 VDC at a current of up to 50 mA. The LED used for lighting consumes the same voltage, but the current is higher - from several hundred mA to 1 A in the project. In the LED module, individual LEDs can be connected in series and the total voltage turns out to be higher (usually 12 or 24 V). When connecting the LED, the polarity must be observed, otherwise the device may be damaged. The breakdown voltage is specified by the manufacturer and is usually greater than 5 V per LED. The brightness of an LED is characterized by the luminous flux and axial luminous intensity, as well as the directional pattern. Existing LEDs of various designs emit at a solid angle of 4 to 140 degrees. Color, as usual, is determined by chromaticity coordinates and color temperature, as well as the wavelength of the radiation. To compare the efficiency of LEDs with each other and with other light sources, light output is used: the amount of luminous flux per watt of electrical power. Also, an interesting marketing characteristic is the price of one lumen. 11. How does the LED respond to a rise in temperature?Speaking about the temperature of the LED, it is necessary to distinguish between the temperature on the surface of the crystal and in the region of the pn junction. The service life depends on the first, the light output depends on the second. In general, with an increase in the pn junction temperature, the brightness of the LED decreases, because the internal quantum yield decreases due to the influence of crystal lattice vibrations. That's why good heat dissipation is so important. The drop in brightness with increasing temperature is not the same for LEDs. different colors... It is higher for AlGalnP and AeGaAs LEDs, that is, for red and yellow, and less for InGaN, that is, for green, blue and white. 12. Why is it necessary to stabilize the current through the LED?As can be seen from the figure, in operating modes, the current exponentially depends on the voltage and small changes in voltage lead to large changes in current. Since the light output is directly proportional to the current, the brightness of the LED is also unstable. Therefore, the current must be stabilized. In addition, if the current exceeds the permissible limit, then overheating of the LED can lead to its accelerated aging. typical volt-ampere characteristics LED 13. Why does the LED need a converter?A converter (in English terminology, driver) for an LED is the same as ballast for a lamp. It stabilizes the current flowing through the LED. 14. Can the brightness of the LED be adjusted?The brightness of the LEDs lends itself very well to regulation, but not by reducing the supply voltage - this just cannot be done - but by the so-called pulse-width modulation (PWM) method, which requires a special control unit (in fact, it can be combined with a unit power supply and a converter, as well as with an RGB matrix color control controller) .The PWM method consists in the fact that the LED is supplied not with a constant, but with a pulse-modulated current, and the signal frequency should be hundreds or thousands of hertz, and the width of the pulses and pauses between them can be changed. The average brightness of the LED becomes controllable, while the LED does not go out. The slight change in color temperature of an LED during dimming is incomparable to the same offset for incandescent lamps. 15. What determines the lifespan of an LED?LEDs are believed to be extremely durable. But it is not so. The more current is passed through the LED during its service, the higher its temperature and the faster aging occurs. Therefore, the service life of high-power LEDs is shorter than that of low-power signal LEDs, and currently amounts to 20 - 100 thousand hours. Aging is expressed primarily in a decrease in brightness. When the brightness is reduced by 30% or half, the LED must be changed. 16. Does the color of the LED deteriorate over time?The aging of an LED is associated not only with a decrease in its brightness, but also with a change in color. There are currently no standards that would quantify the color change of LEDs with aging and compare with other sources. 17. Is the LED harmful to the human eye?The emission spectrum of an LED is close to monochromatic, which is its fundamental difference from the spectrum of the sun or an incandescent lamp. 18. What technologies are available for manufacturing LEDs and LED modules today?As for growing crystals, the main technology is organometallic epitaxy. This process requires highly pure gases. Modern installations provide for automation and control of the composition of gases, their separate flows, precise control of the temperature of gases and substrates. The thickness of the grown layers is measured and controlled in the range from tens of angstroms to several microns. Different layers must be doped with impurities, donors or acceptors in order to create a p-n junction with a high concentration of electrons in the n-region and holes in the p-region. In one process, which lasts several hours, it is possible to grow structures on 6 - 12 substrates with a diameter of 50 - 75 mm. It is very important to ensure and control the uniformity of structures on the surface of the substrates. The cost of installations for the epitaxial growth of semiconductor nitrides, developed in Europe (Aixtron and Thomas Swan) and the USA (Emcore), reaches 1.5-2 million dollars. The experience of different companies has shown that it is possible to learn how to obtain competitive structures with the required parameters using such a facility in a time from one to three years. This is a technology that requires a high level of culture. An important stage of the technology is the planar processing of the films: their etching, the creation of contacts to the n- and p-layers, and the coating with metal films for the contact leads. The film grown on a single substrate can be cut into several thousand chips ranging in size from 0.24x0.24 to 1x1 mm2. The next step is to create LEDs from these chips. It is necessary to mount the crystal in the case, make contact leads, make optical coatings, antireflection surface for radiation output or reflecting it. If it is a white LED, then the phosphor must be applied evenly. It is necessary to provide heat dissipation from the crystal and case, to make a plastic dome that focuses the radiation into the desired solid angle. About half of the cost of an LED is determined by these stages of high technology. The need to increase the power to increase the luminous flux led to the fact that the traditional form of the package LED has ceased to satisfy manufacturers due to insufficient heat dissipation. It was necessary to bring the chip as close as possible to the heat-conducting surface. In this regard, the traditional technology and somewhat more advanced SMD technology (surface montage details) is being replaced by the most advanced technology COB (chip on board). The LED made using the COB technology is shown schematically in the figure. The LEDs made using the SMD and COB technology are mounted (glued) directly onto a common substrate, which can act as a radiator - in this case, it is made of metal. This is how LED modules are created, which can be linear, rectangular or round, rigid or flexible, in short, designed to satisfy any designer's whim. lED bulbs with the same base as for low-voltage halogen, designed to replace them. And for high-power luminaires and spotlights, LED assemblies are made on a round massive radiator. There used to be a lot of LEDs in LED assemblies, but now, as the power increases, there are fewer LEDs, but the optical system, directing the light flux to the desired solid angle, plays an increasingly important role.
iDS technologyArticle source: OOO "Focus"

LED - diode with simple P-N transitionohm, main feature which is that it emits light when a current passes through it. Used in many digital displays as well as other types of display devices.

How the LED works

Basic performance characteristics of any light emitting diode similar to the characteristics of a conventional diode. When a voltage is applied, electrons move from the N-type material through the P-N junction and connect to the holes in the P-type material. In conventional diodes, the energy that results from the connection of electrons with holes is released as heat. However, when it comes to LEDs, the energy in them is released primarily in the form of light.

LEDs can be fabricated to emit red, green, blue, infrared, or ultraviolet light. It does this by changing the amount and type of materials that are used as an additive. The brightness of the light can also be varied by controlling the amount of current passing through the LED. However, like any diode, an LED has a limit on the current it can handle.

Where are LEDs used

One of the main areas of application for LEDs is their use as signal lights. For example, this device can be used to check if there is current flowing through the circuit or if it is de-energized.

A circuit with a signal lamp is a series of devices connected in series with each other: an LED, a resistor, a switch and a source direct current.

When the lamp circuit breaker is closed, forward bias voltage from the current source is applied to the LED (which is designed to operate only when forward bias is present). The electrons that break through the P-N junction connect to the holes, causing the energy to be released as light. A resistor in this circuit restricts the flow of current through it in order to protect the LED from damage caused by excessive current.

LEDs can also be used in digital displays such as wrist watch or calculators.

By highlighting various combinations of seven elements on the display, you can display any number from zero to nine.

Each LED is connected in series with a resistor and a switch, where each switch is an external control circuit. The switches are labeled A through G to match the display elements. Seven serial wires are connected in parallel with a constant current source. In order to supply power to any LED, the corresponding switch is closed. Each series resistor in the circuit limits the current flowing through the wire and thus prevents excessive current damage to the LEDs.

The numbers appear on the digital display as a result of various combinations of seven switches. For example, if switches A and B are closed, the corresponding elements on the display will light up and form the number 1. Similarly, the number 2 can be formed with switches A, C, D, F and G, which will be closed at the same time.

By closing the corresponding switches in certain combinations, the display can get numbers from 0 to 9. If the elements are arranged in a slightly different way, then the display can get a plus, minus, decimal points or alphabet letters.

LEDs can even be used to provide artificial lighting for plant growth. The main advantages of LEDs in this case are: low consumption of electricity and heat generation, as well as the ability to adjust the required radiation spectrum.

LEDs for humanity have become one of the most common light sources for industrial and domestic needs. This semiconductor device has one electrical junction, it converts electrical energy into energy of visible light radiation. The phenomenon was discovered by Henry Joseph Round in 1907. The first experiments were carried out by the Soviet experimental physicist O.V. Losev, who in 1929 managed to get a working prototype of a modern LED.

The first modern LEDs ( LED, LED, LED) were created in the early sixties. They had a faint red glow and were used as turn-on indicators in a variety of devices. In the 90s, blue, yellow, green and white LEDs appeared. Many companies began to produce them on an industrial scale. Today LED diodes are used everywhere: in traffic lights, light bulbs, cars and so on.

Device

An LED is a semiconductor device with an electron-hole junction that produces optical radiation when current flows through it in the forward direction.

The standard indicator LED is made up of the following parts;

1 - Epoxy lens
2 - Wire contact
3 - Reflector
4 - Semiconductor (Determines the color of the glow)
5 and 6 - Electrodes
7 - Flat cut

The cathode and anode are fixed at the base of the LED. The entire device is sealed from above with a lens. A crystal is installed on the cathode. The contacts have conductors that are connected to the crystal by a pn junction (wire connection for connecting two conductors with different types conductivity). For creating stable work LED uses a heat sink, which is necessary for lighting fixtures. In indicator instruments, heat is not critical.

DIP diodes have pins that are mounted in holes printed circuit board, they are soldered to an electrical contact. There are models with several crystals of different colors in one package.

SMD LEDs are the most demanded light sources of any format today.

  • The base of the case, where the crystal is attached, is an excellent heat conductor. Thanks to this, the heat removal from the crystal has improved significantly.
  • In the structure of white LEDs, between the lens and the semiconductor, there is a phosphor layer that neutralizes ultraviolet light and sets the required color temperature.
  • There is no lens in SMD components with a wide beam angle. In this case, the LED itself is distinguished by the shape of a parallelepiped.

The Chip-On-Board (COB) represents the latest practical advancement that is expected to lead artificial lighting in white LEDs.


The design of COB LEDs assumes the following:

  • Dozens of crystals are attached to an aluminum base by means of dielectric glue without a substrate and a case.
  • The resulting matrix is \u200b\u200bcovered with a common phosphor layer. The result is a light source that has an even distribution of light flux without the possibility of shadows.

A variation of the Chip-On-Board is Chip-On-Glass (COG) technology, which involves the placement of many small crystals on a glass surface. For example, these are filament lamps, where the emitting element is a glass rod with LEDs coated with a phosphor.

Operating principle

Despite the technological features and varieties, the operation of all LEDs is based on the general principle of operation of the emitting element:

  • The conversion of electricity into luminous flux is carried out in a crystal, which is made of semiconductors with the most different types conductivity.
  • Material with n-conductivity is provided by doping it with electrons, and material with p-conductivity using holes. As a result, additional charge carriers of different directions appear in the adjacent layers.
  • When a forward voltage is applied, the movement of electrons, as well as holes, to the pn junction starts.
  • The charged particles pass the barrier and begin to recombine, as a result of which an electric current flows.
  • The process of recombination of an electron and a hole in the pn-junction zone is the release of energy as a photon.

In general, the specified physical phenomenon is characteristic of all semiconductor diodes. However, the wavelength of the photon is in most cases outside the visible radiation spectrum. In order for an elementary particle to move in the range of 400-700 nm, scientists have carried out many experiments and experiments with different chemical elements. As a result, new compounds appeared: gallium phosphide, gallium arsenide and more complex forms. Each of them has its own wavelength, that is, its own color of radiation.
In addition, in addition to the useful light that the LED emits, a certain amount of heat is generated at the pn junction, which reduces the efficiency of the semiconductor device. That is why high-power LEDs are designed with efficient heat dissipation.

Varieties

Currently, LED diodes can be of the following types:

  • Lighting, that is, with high power. Their illumination level is equal to tungsten and fluorescent light sources.
  • Indicator - with low power, they are used for illumination in devices.

According to the type of connection, LED indicator diodes are divided into:

  • Double GaP (gallium, phosphorus) - have green and orange light in the structure of the visible spectrum.
  • Triple AIGaAs (aluminum, arsenic, gallium) - have yellow and orange light in the structure of the visible spectrum.
  • Triple GaAsP (arsenic, gallium, phosphorus) - have red and yellow-green light in the structure of the visible spectrum.

By the type of housing, LED elements can be:

  • DIP - outdated low-power model, they are used to illuminate light boards and toys.
  • Piranha or Superflux - analogs of DIP, but with four contacts. They are used for lighting in cars, they heat up less and are better attached.
  • SMD - the most common type, used in a variety of light sources.
  • COB Are advanced SMD LEDs.

Application

The area of \u200b\u200bapplication of LEDs can be roughly divided into two broad categories:

  • Lighting.
  • Using direct light.

LED lighting is used to illuminate an object, space or surface, instead of being directly visible. These are interior lighting, flashlights, lighting of building facades, lighting in cars, key lighting mobile phones and displays and so on. LED diodes are widely used in communicators and cell phones.

Direct LED light is used to transmit information, for example, in full color video displays, in which LED diodes form the display pixels, as well as in alphanumeric displays. Direct light is also used in signaling devices. For example, these are direction indicators and brake lights of cars, traffic lights and signs.

The future of LEDs

Scientists are creating new-generation LEDs, for example, based on nanocrystalline thin films of perovskite. They are cheap, efficient, and durable. The researchers hope that such LED diodes will be used instead of conventional laptop and smartphone screens, including in household and street lighting.

Fiber LED diodes are also being created, which are designed to create wearable displays. Scientists believe that the created method of manufacturing fiber LEDs will allow for mass production and make the integration of wearable electronics into clothing and textiles completely inexpensive.

Typical characteristics

LEDs are characterized by the following parameters:

  • Color characteristic.
  • Wavelength.
  • Current strength.
  • Voltage (type of applied voltage).
  • Brightness (light intensity).

The LED brightness is proportional to the current flowing through it, that is, the higher the voltage, the greater the brightness. The unit of luminous intensity is lumens per steradian, it is also measured in millicandels. There are bright (20-50 mcd.), As well as super bright (20,000 mcd. And more) white LED-diodes.

The magnitude of the voltage drop is a characteristic of the permissible values \u200b\u200bof forward and reverse connections. If the voltage supply is higher than these values, then an electrical breakdown is observed.

The strength of the current determines the brightness of the glow. The current strength of the lighting elements is usually 20 mA, for indicator LEDs it is 20-40 mA.

The light color of the LED depends on the active substances introduced into the semiconductor material.

The wavelength of light is determined by the energy difference during the transition of electrons at the stage of recombination. It is determined by dopants and the original semiconductor material.

Advantages and disadvantages

Among the advantages of LEDs are:

  • Low power consumption.
  • Long service life, measured in 30-100 thousand hours.
  • High light output. LEDs provide 10-250 250 lumens of light output per watt.
  • No poisonous mercury vapor.
  • Wide application.

Disadvantages:

  • Poor performance of low-quality LEDs created by unknown manufacturers.
  • Relatively high price of quality LEDs.
  • The need for quality power supplies.

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Main characteristics of SMD 5730 LEDs

Modern products with geometric parameters of 5.7 × 3 mm. Due to their stable performance, SMD 5730 LEDs are classified as super bright products. New materials are used for their manufacture, due to which they have increased power and highly efficient luminous flux. SMD 5730 can operate in high humidity conditions. They are not afraid of vibration and temperature fluctuations. They are distinguished by a long service life. They have a dispersion angle of 120 degrees. After 3000 hours of operation, the degree does not exceed 1%.

Manufacturers offer two types of devices: with a power of 0.5 and 1 W. The former are marked with SMD 5730-0.5, the latter with SMD 5730-1. The device can operate on impulse current. For SMD 5730-0.5, the rated current is 0.15 A, and when switching to a pulsed operating mode, it can reach 0.18 A. It is able to form a luminous flux of up to 45 lm.

For SMD 5730-1, the rated current is 0.35A, the pulse current can reach 0.8A with a luminous efficiency of 110 lm. Due to the use of a heat-resistant polymer in the production process, the body of the device is not afraid of exposure enough high temperatures (up to 250 ° C).

Cree: actual characteristics

The products of the American manufacturer are presented in a wide range. The Xlamp series includes single-chip and multi-chip products. The former are characterized by the distribution of radiation along the edges of the device. This innovative solution made it possible to organize the production of lamps with a large glow angle with a minimum number of crystals.

The XQ-E High Intensity series is the latest development from the company. Products have a glow angle of 100-145 degrees. With relatively small geometric parameters 1.6 by 1.6 mm, such LEDs have a power of 3 V at luminous flux 330 lm. The characteristics of Cree single-die LEDs allow for high-quality color reproduction of the CRE 70-90.

Multichip LED-devices have the latest type of power supply 6-72 V. It is customary to divide them into three groups depending on the power. Products up to 4W have 6 crystals and are available in MX and ML packages. The XHP35 LED is rated at 13W. They have a dispersion angle of 120 degrees. They can be warm or cold white.

Checking an LED with a multimeter

Sometimes it becomes necessary to test the LED performance. This can be done with a multimeter. Testing is performed in the following sequence:

A photoDescription of work
Cooking necessary equipment... The usual one will do. chinese model multimeter.
We set the resistance mode corresponding to 200 ohms.
We touch the contacts to the checked element. If the LED is working, then it will light up.
Attention! If the contacts are mixed up, no characteristic glow will be observed.

LED color marking

To purchase an LED of the desired color, we suggest that you familiarize yourself with the color symbol included in the marking. For CREE, it is located after the designation of the series of LEDs, and can be:

  • WHTif the glow is white;
  • HEWif high efficiency white;
  • BWT for white second generation;
  • BLUif the glow is blue light;
  • GRN for green;
  • ROY for royal (bright) blue;
  • RED in red.

Other manufacturers often use a different convention. So KING BRIGHT allows you to choose a model with a radiation of not only a certain color, but also a shade. The designation present in the marking will correspond to:

  • Red (I, SR);
  • Orange (N, SE);
  • Yellow (Y);
  • Blue (PB);
  • Green (G, SG);
  • White (PW, MW).
Advice! Check the legend of the specific manufacturer to make the right choice.

Decoding the LED strip marking code

A dielectric with a thickness of 0.2 mm is used to manufacture the LED strip. Conductive tracks are applied to it, having contact pads for chips intended for mounting SMD components. The tape includes individual modules that have a length of 2.5-10 cm and are designed for a voltage of 12 or 24 volts. The module can include 3-22 LEDs and several resistors. The length of finished products is on average 5 meters with a width of 8-40 cm.

A label is applied to the reel or packaging, which contains all relevant information about led strip... The decoding of the marking can be seen in the following figure:

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