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In electronics, light emission led is an optoelectronic device that exploits the possibility of some semiconductor materials to produce photons by means of a spontaneous emission phenomenon.
Emission originates from the recombination of electron-gap pairs according to the principle of the junctional led, characterized by presence in the device of two doped zones differently so as to have different charge carriers.
The first Led was developed in 1962 by Nick Holonyak Jr. In 2014 he was awarded the Nobel Physics Prize to Isamu Akasaki and Hiroshi Amano of Nagoya University and Shuji Nakamura of the University of California, Santa Barbara for Led Light Research blue.
In 1907, Henry Joseph Round published a brief description of the Led Led effect. Twenty years later, Oleg Losev investigated the phenomenon and formulated a theory in a Russian publication.
The first light-emitting diodes were only available in red tones. They were used as indicators in electronic circuits, seven-segment displays and optoisolators. Later, some of them emited yellow and green light and devices were constructed that integrated two Led, usually one red and one green, in the same container allowing to display four states (off, green, red, green + red = yellow) With the same device.
There are currently "two-colored" Leds that integrate in the same body two Led anti-parallel, each of different colors; Thus, to vary the color of the LED, it is sufficient to power it with opposite polarity. The only disadvantage is that different colored Leds need different (If) currents to produce a certain luminous intensity; So, for example, in a red / green bicolor led, the green will have a light intensity smaller than that of red, at the same current.
In the 1990s, Led was manufactured with ever increasing efficiency and a growing range of colors, until, with the introduction of blue light led, it was possible to create devices that could generate any color by integrating three Led in red, green and blue. Equally, the amount of light emitted at competitive levels with those of ordinary bulbs has increased. In lighting engineering, the Led is a high-efficiency technology that delivers great energy savings.
P-n junction leds are a particular type of Led formed by a thin layer of semiconductor material. Electrons and gaps are injected into a recombination zone through two Led drug regions with impurities of different type, that is, type n for electrons and p for gaps.
When subjected to direct voltage to reduce the junction potential barrier, the semiconductor conductor band electrons recombinate with the valence band gap by releasing sufficient energy in the form of photons. Due to the reduced thickness of the chip a reasonable number of these photons can abandon it and be emitted as light or optical photons. It can also be seen as an electro-optical transducer.
The color or frequency of the emitted radiation is defined by the distance in energy between the electron energy levels and gaps and typically corresponds to the value of the forbidden band of the semiconductor concerned. The exact choice of semiconductors therefore determines the wavelength of photon peak emission, the efficiency in electro-optical conversion, and hence the output light intensity. The LEDs can be formed from gallium arsenide (GaAs), gallium phosphate (GaP), gallium arsenic phosphide (GaAsP), silicon carbide (SiC) and gallium and indium nitride (GaInN).
The LEDs affected by visible light, infrared or ultraviolet light spectrum, depending on the Led used as a receiver, produce electricity exactly like a photovoltaic module. The blue and infrared LEDs produce considerable voltages. This feature makes it possible to apply LEDs for light pulse reception systems. Around this property many industrial products have been developed such as distance sensors, color sensors, tactile sensors and transceivers. In the field of consumer electronics, the irDA communication system is a good example because it fully exploits this peculiarity.
The LED has a very variable life time depending on the luminous flux, working current, and operating temperature.
The LED can have an output:
The LED spectrum varies greatly depending on the LED. If the LED is used for lighting, it generally has a good coverage of its spectrum, which can also be exploited to 100%; In other applications there are LEDs that emit unseen light.
Depending on the material used, the LEDs produce the following colors:
The need to have a wide variety of color tones in white light, a prevalent need for lighting in buildings, has led manufacturers to significantly differentiate these devices based on color temperature; On the market there are selected devices and subdivided up to 6 temperature ranges, ranging from 2700 K ("hot" shades) to over 8000 K ("cold" light).
The LEDs are particularly attractive for their high luminous efficiency A.U./A and reliability.
The evolution of materials has been the main road to obtain light sources that have the characteristics to replace almost all those used today.
In the earliest mobile phones they were present in the smallest commercial format for keystroke lighting. Currently, the smallest emitting chips constitute the active zone of the Led Chip On Board (COB), tiny DIE strips matched directly on the substrate of the device. On some new models of cars and mopeds there are replacing filament lamps for "position" and "stop" lights. Already there are direct replacement devices for spotlights and halogen bulbs, which have the same dimensional standard. For street lighting there are lamps similar to the traditional ones. The amount of light required for each application is made with die matrices in number.
The increase in efficiency is constantly increasing.
The LEDs are fed with a polarized constant current, the value of which is indicated by the manufacturer in its datasheet. This can be achieved by using a current generator or more simply by setting a suitable value resistor in the Led array, with the task of limiting the current flowing to it. In this case the excess power is dissipated into heat in the led-connected limiting resistor (this solution penalizes the system's efficiency and, due to the resistive variation of the system according to the temperature at which it works, does not accurately guarantee the LED A current flow corresponding to the manufacturer's specifications).
If they are powered by alternating current, it is necessary to protect them by placing them in parallel with a Led with an inverted polarity with respect to the Led ("antiparallel").
Rarely, you can use a four-lane bridge to ensure that a direct current always runs through the led.
If you want to power a Led with the mains voltage without the circuit dissipating too much energy in the series resistance, you can use a circuit consisting of a condenser connected in series to a section that consists of the Led parallel to a protection Led , Still in series, a protective resistor used to limit the discharge at power-on.
The maximum amount of light that can be emitted by a LED is essentially limited by the maximum bearable media current, which is determined by the maximum power dissipable by the chip.
They are characterized by three main parameters: power in W, current supplied in mA on one or more outputs, and output voltage. The output voltage is not fixed, but is between a minimum and a maximum, to ensure that the current is kept constant at its nominal value. The voltage supplied will depend on the type of Led used and their number.
Usually the longer terminal of a led indicator (diameter diameter 3 mm, 5 mm or higher) is the anode (+) and the shortest one is the cathode (-).
If the LED is already welded to the plate or the terminals have been cut to the same size and / or it is not possible to recognize the polarity from the terminals, if you observe closely inside the plastic casing you will notice a larger cathode terminal (-) and one Smaller anode (+) exactly the opposite of what happens to the external terminals.
To properly polarize a led we can also take advantage of a particular feature of the package: if you look at the led from above, you may notice that the side of the package is not regular, but square on the one hand: this "squaring" Cathode (-). In the case of 3 mm led, a tester should be used as such "sign", if present, is almost unseen.
If you use a tester after selecting the resistance scale with factor 1 (X1), if you put the positive on the anode and the negative cage on the cathode, the tester will mark a resistance value of a few hundred Ohm, if the tester was an analog model with a 3 volt power battery, if the LED is efficient, being directly polarized, the small current stream that will cross it will turn it on, turning the tips, instead, the tester will not have to Mark any continuity.
The input power supply in the device varies greatly depending on the type of LED: they are smaller in normal LEDs used as indicators than high brightness (flash and power LEDs).
The Led in these years have spread to all applications where it is needed:
Some major uses:
Since 2006, the city of Raleigh - North Carolina - is considered the first Led city in the world for the technological renewal to promote the use of lighting in Led.
The Led's commercial strength is based on its ability to achieve high brightness (many times greater than that of tungsten filament lamps), low price, high efficiency and reliability (the lifetime of a LED is one-two orders Of greater magnitude than that of classic light sources, especially under mechanical stress). Led works low voltage, has high switching speed and construction technology is compatible with that of silicon integrated circuits.
A Led SMD module is a type of Led module that uses surface mount technology (SMT) to mount Led Chips on PCBs.
Led is increasingly used in lighting technology to replace some traditional light sources. The use of home lighting, instead of incandescent lamps, halogen lamps or compact fluorescents (energy saving calls), is now possible with remarkable results achieved thanks to innovative techniques developed in the field.
At the beginning of the research the luminous efficiency of light / consumption (lm / W) was calculated in the minimum ratio of 3 to 1, after which it was greatly improved.
As a comparison term, think that an incandescent lamp has a luminous efficiency of about 10-19 lm / W, while a halogen lamp is about 12-20 lm / W and a fluorescent linear about 50-110 lm / W.
Led manufacturers are semiconductor manufacturers, silicon factories, and bulbs are mainly manufactured by other manufacturers, so there is a delay between the date of placing a new Led device on the market and the market availability of a bulb that Use it.
The advantages of Led from the lighting point of view are:
The disadvantages are:
