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How Light Emitting Diodes Work (LEDs)

By Andrew Fraser on 12.29.2018 in Scotlight Direct , , , , , , , , , , , ,

How Light Emitting Diodes Work

The main function of the Light Emitting Diode is to turn electrical energy into visible light. The history of LEDs stretches back over 100 years, from the first experimental discoveries, to their many uses and applications today.


LEDs come in a few different forms, and there are key differences in how each type works.

This article will attempt to explain how LEDs work, in an easy to follow format, with as little confusing scientific jargon as possible.

Technology of the LED

The Underlying Technology of the Light Emitting Diode

What is a Semiconductor?

Within the context of the study of electronics, understanding the association between matter and electricity is fundamentally important. This is because every electronic device is assembled using parts created from ordinary matter. Therefore, in order to understand electronics at a basic level, it is important to understand the effects of electricity on matter.

For the purposes of accomplishing this, all the elements from which matter is made are separated into three distinct categories.


These are: Conductors, Insulators and Semiconductors.


For the purposes of this article, the focus will be on understanding semiconductors, but it is also important to know how they work in relation to conductors and insulators.


Conductors are elements like copper and silver which conduct the flow of electricity very readily. They are usually formed as wire, and used to transfer electrical energy between two points.


Insulators do not readily conduct the flow of electricity, and are used in practice when it is necessary to prevent the flow of electricity. Materials which fall within this definition include sulphur, rubber and glass.


Semiconductors fall in-between the categories of conductors and insulators, as they don’t perform either of these functions effectively. The characteristics of semiconductors fall between those of conductors and insulators.


Materials which are semiconductors include germanium, silicon and the variety of elements used in LEDs, including; zinc sulphide, gallium arsenide and gallium nitride.

What Is A Semiconductor?

Discovering Electroluminescence

Electroluminescence is both an optical and an electrical phenomenon, where materials emit light as they respond to electrical current, either as a conductor, or when are within range of a sufficiently strong magnetic field.


The mechanism by which electroluminescence works depends on a radiative recombination of charged electrons, and spaces within a semiconductor, which release energy as photons.


We perceive this as light.


In LEDs, before the radiative recombination occurs, there are two main methods by which the amount of light they emit can be enhanced.
These form the basis of the LEDs in commercial usage today.


N-Type and P-Type Semiconductors
The first method is by separating the electrons and spaces in the semiconductor by using what’s known as a ‘doping’ conductor, to form a p-n junction.


In a p-n junction the ‘n’ stands for ‘negative’, and the ‘p’ stands for ‘positive’.
N-type semiconductors can be made by adding some atoms from the element antimony to silicon, which will allow extra electrons to pass through it.


In p-type conductors the atoms of an element like boron can be added, and this will remove electrons from the silicon, leaving holes where the electrons once were. This allows the electrons to move around carrying a positive charge.


Doping, in the context of producing semiconductors, is the synthetic introduction of impurities to an intrinsic (or un-doped) semiconductor, so that its electrical, structural and optical properties can be modulated.


The other method takes place through excitation by causing the impact of highly charged electrons which is accelerated by a strong electrical field. This method is used in electroluminescent displays, such as those used for aircraft instrument panels. In this instance the phosphors are the materials being exposed the electromagnetic field.


Junction Diodes


Things get interesting when p-type and n-type silicon semiconductors are combined.


If you add a piece of n-type silicon, with too many electrons, to p-type silicon, electrons from the n-type side will move across the join, so that they can fill the holes in the n-type side, as the silicon is returning to its normal state again.


As silicon does not readily conduct electricity, and neither does the junction that has been created, a barrier is created between the n-type silicon and the p-type silicon.


This is known as a depletion zone, due to the fact that it contains neither free electrons or holes.


If you were to connect a battery to the newly formed p-n junction, the way in which it has been connected will influence the outcome.


Forward Bias


If the negative side of the battery is connected to the n-type silicon, and the positive side to the p-type, this will cause the size of the depletion zone to be reduced. Electrons and holes will cross the junction in an opposite direction and current flows, causing what is known as a forward bias.


Reverse Bias


If the poles of the battery are connected in the opposite way, so that the positive side is connected to the n-type silicon, and the negative side to the p-type silicon, this will cause the electrons to travel to the opposite end of the from the holes, which travel in the other direction. No current can flow in these circumstances, this is called a reverse bias.


This basically explains the function of an ordinary diode, and why electric current is only able to travel through them in one direction.

Terms Used in LED Technology


How LEDs Work (in a nutshell)


LEDs are basically diodes which are designed in a way which allows them to give off light.


A forward bias diode which allows the electrons and holes to pass through the depletion zone in opposite directions will allow them to combine and thus eliminate each other.


After a certain amount of time, when an electron moves from the n-type to the p-type silicon, it will find a hole to combine with and disappear.


This process completes an atom, also making it more stable, and as this happens it will give off a small burst of energy in the form of a single photon of light.

Inventors Of The LED

Early Inventors of the LED

H. J. Round


In 1907 H. J. Round discovered electroluminescence.


He investigated what would happen if he unsymmetrically passed current through silicon carbide using a cat’s whisker detector.


When he applied an electrical potential of 10 volts between two points on the silicon carbide, he noticed that the crystals gave off a yellowish light.


He also introduced 110 volts, and it was at this point that some of the crystals gave off green, orange and blue light instead of yellow.


He noted that in every test he conducted, the glow appeared at the negative pole.


H.J Round published these finding in the journal Electrical World and made an appeal at the end of the article for “references to any published account of an investigation of this or any allied phenomena.”


Oleg Losev


The next step in the evolution of LED lighting is attributable to the Russian Scientist, Oleg Losev, who was the first to properly investigate their effects, provide a detailed theory of how they could work, and he also described the possible practical applications. He published these findings in a Russian Journal in 1927.


Losev’s major contribution was to explain the function of a solid-state light source, which could generate light by electroluminescence.

Georges Destriau


It was almost twenty years before Georges Destriau took the next step in the evolution of LEDs.


In 1936 Destriau observed that he could produce electroluminescence by suspending zinc sulphide in an insulator, and then introducing an alternating electrical field.


He referred to this type of luminescence as ‘Losev Light’, in reference to the Russian scientist who was giving more scientific basis to the findings of H.J Round, as well as discovering the possible applications of his inventions.


Kurt Lehovec


Kurt Lehovic also cited the work of Oleg Losev in his work, as he explained the first light emitting diodes together with Edward Jamgochain and Carl Accardo.


Along with his colleagues, Lehovic explained early Light Emitting Diodes in 1951.


They used an apparatus which employed silicon carbide crystals with a battery as a source of current, or a pulse generator and they also created a comparison with a variant, pure silicon crystal.


James R. Biard


It was in 1961 that James R. Biard and his colleague Gary Pittman made the discovery of near infra-red light being emitted by a tunnel diode while working for Texas Instruments.


Following this discovery, the US patent office awarded a patent to what was the first practical LED.


Nick Holonyak Jr.


In 1962 Nick Holonyak Jr. invented the first visible spectrum LED while he was working at General Electric.


Kurt Lehovic also cited the work of Oleg Losev in his work, as he explained the first light emitting diodes together with Edward Jamgochain and Carl Accardo.


Along with his colleagues, Lehovic explained early Light Emitting Diodes in 1951.


They used an apparatus which employed silicon carbide crystals with a battery as a source of current, or a pulse generator and they also created a comparison with a variant, pure silicon crystal.


James R. Biard


It was in 1961 that James R. Biard and his colleague Gary Pittman made the discovery of near infra-red light being emitted by a tunnel diode while working for Texas Instruments.


Following this discovery, the US patent office awarded a patent to what was the first practical LED.


Nick Holonyak Jr.


In 1962 Nick Holonyak Jr. invented the first visible spectrum LED while he was working at General Electric.

Inventors Of The LED
LED Lighting Explained

What is LED Lighting?

The First LEDs


Early versions of the LED, as invented by Nick Holonyak Jr, were red. This was not out of choice.


LEDs are made by layering semiconductor materials onto a wafer-like surface. As the layers are built up, doping materials are added, and these will determine the colour of the LED.


The doping agent used in the first LEDs was gallium arsenide phosphide, and this produces a red colour naturally.


This part of the reason that red became the default colour indicator lights, though the fact that red is also natures colour for danger must have helped their adoption.


Modern processes for creating doping agents mean that LEDs are now available in choices from across the colour spectrum, leading to many more applications than just as power indicators or warning lights.


For the first decade of their working life, LEDs were available only in red.


The Many Jobs an LED Can Do


LEDs are a one of the most widely used components in electronic circuits. They do scores of jobs and are found in a wide variety of devices.


This includes the numbers on digital clocks, sending information from remote controls and as indicator lights which tell us when appliances are turned on.


They can also be combined in a matrix, and used as a jumbotron type television screen, or as the illumination for traffic lights.


The LEDs used for these types of jobs are basically just small lamps which can be easily applied to an electrical circuit.


They are preferred over incandescent light sources because they are longer lasting and emit less heat. The key feature in this is that they do not have a filament which can burn out or be easily damaged.

Uses for LED Lighting In The Modern Age


Modern Uses of LEDs


White Light


LEDs made the advance from indicators light or information displays to becoming light sources in 1993. Shuji Nakamura made a breakthrough when he discovered a doping process which led to bright blue LEDs.


Following this, yellow phosphor was used to coat the blue LED and this is how we got white LEDs.


This provided for a whole variety of new applications, and they could now illuminate the world.


One of the first jobs white LEDs did was in flashlights, and now it would be near impossible to find a flashlight with an old incandescent light source.

Lighting Up the Road


Replacing car headlamps can be difficult. Different types of enclosures, proprietary clips and lack of space between engine components can all block access to the lamp.


In modern cars, the old incandescent type bulbs have been replaced by LEDs, meaning that they will probably never need to be replaced, and may even outlast the car.


By 2010 nearly every car was fitted with LED headlamps, with a combination of long life-spans and low energy usage making them ideal for use in vehicles.


Besides all the practical upside, they look great as well.


Replacing the Light Bulb


Compact fluorescents were a big step forward in terms of energy efficiency when compared to incandescent light sources. However, they created a horrible ambiance, and were not very adaptable or aesthetically pleasing.


It was inevitable that incandescent lights would be replaced, but compact fluorescents are not capable of creating the warm light required to create a comfortable environment.


LEDs have the flexibility to create warm light, and they can do so using a lot less electricity, though they do create a lot of heat.


They can also be expensive, but this hasn’t stopped huge companies like Philips and General Electric from investing in the development of new and more efficient types of LED lighting, and they are have become the dominant light source over the last number of years.

Uses For LED Lighting In The Modern Age


A Guide To How LED Light Bulbs Work

How Do LED Light Bulbs Work?

Replacing Traditional Light Sources


Over the last number of years LED bulbs have been replacing traditional incandescent light bulbs and the more modern compact fluorescent light bulbs.


LED bulbs can be screwed into the same sockets as incandescent light bulbs and CFL’s.


Early versions of LED replacements could appear not as bright as the bulbs they were replacing. While LED bulbs have always produced a lot of light, the tendency in the early days was for that light to get trapped inside.


However advancements in LED technology means that this is no longer a problem, and it is easy to find LED bulbs which can emit as much light as a 60 watt incandescent bulb while using only 10% of the energy.

How LED Light Bulbs are Improving


The top lighting companies like Philips and General Electric are investing a lot of money into researching and improving LED lighting.
This investment is leading to many breakthroughs in efficiency and reductions in the cost of producing high efficiency bulbs which will last for a very long time.


Solving Light Loss


As mentioned earlier in the article, one of the major problems of LED lighting is light loss. This is being solved by putting microscopic holes in the casing of the bulb to help with releasing the light. This process can be expensive, however a new technique using nano-imprint lithography which can put billions of holes in the tiny LEDs is solving this problem.


Reducing Production Time


There are also advancements being made in the production of the LEDs themselves. Newer more cost-effective techniques of creating the gallium nitride semiconductors, using silicon wafers instead of the more expensive sapphire wires which were used in early versions of LED lighting. This has led to a dramatic reduction in the costs of producing LEDs.


This is good news for consumers of LED lighting, as they are getting better quality lighting at a reduced cost. When this is added to the savings which are possible from the reduced energy usage, there is not much of an argument for using any other light source.

A Guide On How LED Light Bulbs Work