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what is a Led flat light

What is led?


Light-emitting diode referred to as LED. Is made of a compound containing gallium (Ga), arsenic (As), phosphorus (P), nitrogen (N) and the like.

When the electrons recombine with the holes, they can emit visible light, and can be used to make light-emitting diodes. In the circuit and instrument as an indicator, or the composition of text or digital display. Gallium arsenide diode red light, gallium phosphide diode hair green, silicon carbide diode yellow, gallium nitride diode blue light. Because of its chemical properties are divided into organic light-emitting diode OLED and inorganic light-emitting diode LED.
Led technology principle?

It is a kind of semiconductor diode that can convert electrical energy into light energy. LED and the development of ordinary two-chip LED chip LED chip development tube is composed of a PN junction, also has a one-way conductivity. When a positive voltage is applied to the LED, holes injected from the P region into the N region and electrons injected from the N region into the P region are separated from the N junction and the P region by a few micrometers Point complex, resulting in spontaneous emission of fluorescence. The energy states of electrons and holes in different semiconductor materials are different. When electrons and holes recombine, the energy released is much different, the more energy is released, the shorter the wavelength of light is. Commonly used is the red, green or yellow light of the diode. The reverse breakdown voltage of the light-emitting diode is greater than 5 volts. Its positive volt-ampere characteristic curve is very steep, must be used in series to limit the current limiting resistor to control the current through the diode. Current limiting resistor R can be calculated as follows:

R = (E – UF) / IF

Where E is the supply voltage, UF is the LED forward voltage drop, IF for the LED’s normal operating current. The core of the light-emitting diode is composed of P-type semiconductor and N-type semiconductor wafer, in the P-type semiconductor and N-type semiconductor between a transition layer, known as the PN junction. In some semiconductor materials PN junction, the injection of minority carriers and majority carrier recombination will be the excess energy in the form of light released, so that the power directly into light energy. PN junction plus reverse voltage, a small number of carriers is difficult to inject, it is not light. The use of injection-type electroluminescent light-emitting diodes made of the principle called light-emitting diodes, known as LED. When it is in the positive working state (that is, plus the forward voltage at both ends), the current flows from the LED anode to the cathode, the semiconductor crystal to issue different colors from ultraviolet to infrared light, light intensity and current related.
LED unidirectional conductivity

The LED can only be turned on in one direction, called forward bias (forward bias). When current flows, electrons and holes recombine in it to emit monochromatic light, which is called electroluminescence , While the light wavelength, color and semiconductor materials used with the types of impurities associated with the incorporation of elements. With high efficiency, long life, easy to break, high switching speed, high reliability and other advantages of less than traditional light sources. White LED luminous efficiency, in recent years has been significantly improved, while the purchase price per thousand lumens, but also because of the impact of competition in the market vendors, and decreased significantly. Although more and more people use LED lighting for office, furniture, decoration, signs and even street use, but technically, LED in the photoelectric conversion efficiency (effective illumination on the ratio of electricity consumption) is still lower than the new fluorescent lamps, is The future development of civil whereabouts of the state.

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Luminous intensity and light intensity distribution

LED luminous intensity is the characterization of its luminous intensity in a certain direction, due to the LED in different spatial angle light intensity difference, followed by the study of the LED light intensity distribution. This parameter is of great practical significance, a direct impact on the LED display device minimum viewing angle. Such as stadiums LED large color display, if the choice of LED tube distribution is very narrow, then the face of the display at a larger angle of the audience will see the distortion of the image. And traffic lights also require a wide range of people can identify.
Led status quo

LED technology in the 20th century, 90’s great progress, not only the luminous efficiency than incandescent, light intensity to the candle level, and the color from red to blue cover the entire visible spectrum range, this level from the light to more than GM The technological revolution in light level has led to new applications such as car lights, traffic lights, large full-color outdoor displays, and special lighting sources
Light-emitting diode applications:

As light-emitting diodes become more bright and multicolored, applications continue to expand, from lower-light indicators to displays, from outdoor displays to medium-luminous power lights and special illuminated white light sources, and finally, The development of the upper right corner of the high luminous flux of general lighting .2000 is the time line in 2000 has resolved all the color signal display problems and lighting problems, and has begun low and medium luminous flux of special lighting applications, and as General Lighting Of the high luminous flux of white light applications, it seems that remains to be seen, the need for further substantial increase in luminous flux can be achieved only, of course, this is a process, will increase with the brightness and price reductions and gradually.
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LED type of development
The first application of semiconductor P-N junction light made of LED light source theory came out in the 20th century, the early 60s. At that time the material used is GaAsP, red light (λp = 650nm), the drive current of 20 mA, the luminous flux is only a few thousandths of a lumen, the corresponding luminous efficiency of about 0.1 lumens / watt.
In the mid-1970s, the introduction of the elements In and N led to green light (λp = 555nm), yellow (λp = 590nm) and orange (λp = 610nm), and the luminous efficiency was increased to 1 lumen / Watt.
To the early 80s, there GaAlAs the LED light source, making the red LED light effect to 10 lumens / watt.
The early 90s, red, yellow GaAlInP and hair green, blue GaInN two new materials successfully developed, so that LED light efficiency has been greatly improved. In 2000, the former made the LED in the red, orange (λp = 615nm) of the luminous efficiency of 100 lumens / watt, while the latter made in the green LED area (λp = 530nm) light efficiency can reach 50 lumens / watt.
Application of monochromatic LED The initial LED as the instrumentation of the light source, and later a variety of light color LED traffic lights and large area display has been widely used, resulting in a very good economic and social benefits. To 12-inch red traffic lights, for example, in the United States would have been using long-life, low-efficiency 140-watt incandescent light source, which produces 2000 lumens of white light. The red filter, the light loss of 90%, leaving only 200 lumens of red light. In the new design of the lamp, Lumileds company uses 18 red LED light source, including circuit losses, including a total power consumption of 14 watts, can produce the same light efficiency.
Automotive light source is also an important area of ​​application of LED light source. In 1987, China began to install high-speed brake lights in the car, because the LED fast response (nanosecond), you can let the driver of the trailer as early as possible to know the driving conditions, reduce the car rear-end accidents.
How to improve the LED drive power factor?

The ENERGYSTAR Solid State Lighting (SSL) specification of the US Department of Energy (DOE) mandates power factor correction (PFC) at any power level. This standard applies to a range of specific products, such as downlights, cabinet lights and table lamps, where the LED driver power factor for residential applications must be greater than 0.7 and commercial applications greater than 0.9; however, this standard is a voluntary standard. The IEC61000-3-2 Harmonics Standards of the EU specifies total harmonic distortion (THD) performance for lighting applications with powers greater than 25 W, with a maximum limit of THD <35% and a power factor (PF )> 0.94. While not all countries are absolutely mandated to improve the power factor in lighting applications, some applications may require such utilities to vigorously promote the commercial use of products with high power factor in the utility, and utilities Organizations that purchase / maintain streetlights can also decide whether to require a high power factor (usually> 0.95+) depending on their wishes. “Read the full article”
1 led high-brightness single-color light-emitting diodes
High-brightness monochrome light-emitting diodes and ultra-high brightness monochrome light-emitting diode semiconductor materials used in ordinary monochrome light-emitting diodes, so the intensity of light is also different. Typically, monochrome high-brightness light-emitting diodes using arsenic gallium arsenide (GaAlAs) and other materials, ultra-high brightness monochrome light-emitting diodes using phosphine indium gallium arsenide (GaAsInP) and other materials, and ordinary monochrome light-emitting diode gallium phosphide (GaP ) Or gallium arsenide (GaAsP). Commonly used high-brightness red light-emitting diode of the main parameters in Table 4-29, commonly used ultra-high brightness monochrome LED’s main parameters in Table 4-30.
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2 led color change light-emitting diodes
A color-changing light-emitting diode is a light-emitting diode capable of converting an emission color. Color light-emitting diode light-emitting color types can be divided into two-color light-emitting diodes, three-color light-emitting diodes and multi-color (red, blue, green and white four colors) light-emitting diodes. Color-changing light-emitting diodes can be divided according to the pin number of two-color light-emitting diodes, three-color light-emitting diodes, four-color light-emitting diodes and six-color light-emitting diodes. Commonly used two-color light-emitting diodes with 2EF series and TB series, commonly used three-color light-emitting diodes are 2EF302, 2EF312, 2EF322 and other models.
3 AC welding machine with a steep drop in voltage characteristics
General electrical equipment requires the power supply voltage does not change with the load changes, the voltage is constant, such as 380V (single phase) or 220V. Although the voltage of the welding transformer is fixed, such as 380V or 220V, the voltage outputted by this transformer can change with the change of output current (load), and the voltage decreases rapidly with the increase of load. Called the steep drop characteristic or the descending characteristic. This accommodates a variety of voltage requirements for soldering:
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4 led flashing light-emitting diodes
Flashing light-emitting diode (BTS) is a CMOS integrated circuits and light-emitting diode consisting of special light-emitting devices can be used for alarm indication and under-voltage, over-voltage indication. Flashing light-emitting diode in use, no external components, as long as the pin at both ends with the appropriate DC voltage (5V) to flash light.

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