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. LEDs are now used in a range of applications and light fittings such as outdoor wall lights, bedroom ceiling lights, and even
This article will attempt to explain how LEDs work, in an easy to follow format, with as little confusing scientific jargon as possible.
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
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
Insulators do not readily conduct the flow of
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.
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
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
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
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
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
This basically explains the function of an ordinary diode, and why electric current is only able to travel through them in one direction.
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.
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
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
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
He referred to this type of luminescence as ‘Losev Light’, in reference to the Russian scientist who was giving
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
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
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
Kurt Lehovic also cited the work of Oleg Losev in his work, as he explained the first light emitting diodes together with Edward
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
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
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
The doping agent used in the first LEDs was gallium arsenide phosphide, and this produces a red
This part of the reason that red became the default
Modern processes for creating doping agents mean that LEDs are now available in choices from across the
For the first decade of their working life, LEDs were available only in red.
The Many Jobs an LED Can Do
LEDs are
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.
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,
This provided for a whole variety of new applications, and they could now illuminate the world. In particular, the commercial and domestic lighting industry was transformed. Items such as outside wall lights and many domestic lights could be used with LED lamp bulbs instead of traditional halogen lamps.
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
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.
Lighting Your Home
Many households have benefited from this as common lights sources such as ceiling spotlights which you find in many kitchens and living rooms had previously consumed a large amount of electricity. With the change over to LED lighting, this has drastically reduced the running cost for this type of low ceiling lighting
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.
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
Solving Light Loss
As mentioned earlier in the article, one of the major problems of LED lighting is
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.
Author Profile
- Adam is an in-house technical writer for Scotlight Direct, a website dedicated to providing the latest and most accurate information on lighting topics. With a passion for writing and a deep understanding of various lighting concepts and designs. Adam has been a valuable asset to the team since joining in 2019.
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