How LEDs work, the cheapest and most resistant light source on the market

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Credits: Zishan khan, via Unsplash.

Miniaturizablelight, durable and powerful: from the screen of our phones to public lighting, I LED (Light emitting diode) have now crowded out all other sources of light, offering intense lighting and bright colors with Low consumption.

The interest in this technology is such that even institutions, such as the European Union, have decided to encourage its diffusion, by banning the sale of old incandescent bulbs from 2012 and following the same path for halogen lamps, partially banned from 2018.

Where do these virtues of LEDs come from and why did their diffusion only begin in the 2000s?

The origins of LEDs

Electric lighting originated in the early 1800s, but did not become established until the 1879with the entry into the market of incandescent bulbs Of Thomas Edison. In the early 1900s, new light sources, such as neon or LED lights fluorescencethey provided a more effective alternative, a energy saving and long-lasting compared to traditional bulbs, but they have never managed to replace them due to defects such aslight emission (measured in lumens) reduced light and more “artificial” for the human eye.

Also at the beginning of the 20th century, the English engineer Henry Joseph Round discovered theelectroluminescence of the semiconductor diodesthat is to say the capacity of certain materials to emit light if it is subject to a Electric power. LEDs are special diodes developed to exploit this phenomenon and were born in 1961 with the introduction of led a infraredstill widespread today in remote controls or photocells.

Already the following year, Nick Holonyak Jr. invented the first Red LEDtherefore capable of emitting visible light to the naked eye. Studies on these diodes and possible applications (for example in laser) focused on the materials used in order to obtain different colors or shades, working with several sources at once.

Among the main protagonists of these studies, the American engineer Mr George Craford (former student of Holonyak at the University of Illinois) at 1972 I managed to create first yellow LEDs distributed commercially by the company for which he worked, the Monsanto. Crafrord has devoted his entire career to the world of LEDs: it is also thanks to his studies that we owe the first large-scale distribution of these light sources, used for example in traffic lights and public light signaling.

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LEDs have been used for decades in road signs and are also becoming widespread in our cars. Credits: Mark Boss, via Unsplash.

The final turning point has come 1994 by the Japanese engineer Shuji Nakamura and his studies on High intensity blue LED: upgrade the light Source and use it to trigger the phosphorescence Using the substances deposited on the diode, LED bulbs suitable for lighting buildings were eventually created, often reducing the energy required by 7 to 10 times.

How LED works

But how is an LED made? Since their birth, these devices have been based on the use of semiconductorsthat is, materials (such as Silicon oldGallium arsenide) That normally not I am good current conductors but they can still become so thanks to external energy sources such as heat or light.

What makes a material a conductor is the characteristic it possesses “free” electrons“, capable of moving along the material following a potential difference (called more simply ddp). The electrons possessed by each atom have in fact different energies, the higher the further they are from the nucleus: when one of them has a sufficiently high energy to reach the conductive tapebecomes free to circulate and is no longer linked to its atom.

In the metalseven without external intervention the electrons of valence band they can move on to conductive tape because these are superimposable. Conversely, a insulating has significant energy jumps, it therefore does not conduct electricity under normal conditions.

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In semiconductors, a small amount of energy is enough to make the valence electrons “jump” to the higher energy band. The reverse path will see the electron lose excess energy, such as light or heat, depending on the jump.

In the case of semiconductors, the energy jump And down. The energy required for the jump depends on the material used, but also on doping, that is to say the introduction of elements such as phosphorus or boron into the crystal structure of the material: this causes an abundance of negative (n) or positive (p) charges in the “drugged” material.

Posing two semiconductors in contact negative and positive charges accumulate at the junction: THE electrons in the conductive tape they go from the material richest in electrons (n) to the positively charged one (p) and here they decompose At valence bandreleasing excess energy in the form of light.

This process is much more efficient than that of incandescent bulbs, because greatly reduces loss of heat or infrared rays invisible to the naked eye: if a traditional bulb the energy transformed into light is a maximum of 5%, in the case of LEDs theefficiency is generally 15% or more, always from an already lower consumption.

Losses in the form of heat are, however, high: this means that for higher power LEDs (such as those in car or motorcycle headlights, which can consume tens of W), measures are necessary to dissipate it, generally with metal fins Or Fans to force cooling. A poor dissipation increased to reduction of light emission it’s at defaultsand is the primary cause of failure of the cheapest bulbs, given the simplicity and robustness of LEDs.

The energy saving of LEDs

The low consumption characteristic is the characteristic that has most interested institutions interested in energy saving for environmental reasons but also infrastructural: this is the reason which led the EU to ban incandescent bulbs.

Despite a higher but constantly decreasing price, an LED lamp consumes up to 60% less than a fluorescent lamp and up to 95% less than incandescent lamps: a saving that is certainly significant for us consumers, but even more significant for Municipalities, whose public lighting can be responsible for up to 25% of energy consumption.

In a world of energy crisis and waste, LEDs now represent a valuable ally in reducing greenhouse gas emissions and electricity consumption, helping us get closer to the Kyoto targets and strengthening our efforts against climate change .

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