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It's A Blue Worl(e)d - MyScience [archived]


It's A Blue Worl(e)d

LEDs. We’ve all heard about them. In our TVs, in our computer monitors, and in our homes. It’s a word we hear often – but do we really know what it means?
We sent Vitória Barim Pacela, our light emitting diode correspondent, to find out how LEDs revolutionised our world’s light

LEDs. Photo: Wikimedia Commons/Afrank99

LEDs. Photo: Wikimedia Commons/Afrank99

Light has always been vital for life. Nowadays, it also means advances in science and technology, for example in the fields of photonics and optoelectronics – light has become another way to transmit information.

LED stands for Light Emitting Diode. A diode is an electronic component, which only allows current to flow through it in one direction. If enough positive voltage is applied to the LED, a current will flow through it and the LED will send out – emit – light. This effect is known as electroluminescence.

But exciting electronic circuitry aside, LEDs are immensely useful and consume a lot less energy than the traditional light bulbs. They are very energy efficient, have longer lifetime, and give more adjustable lighting than regular light bulbs. Needing much less energy to provide the same amount of light as traditional light bulbs, emitting less heat as well – you’re probably getting the point. This means if you use LEDs for your home, your electricity bill will be smaller, and who doesn’t want that?

How LEDs work. Photo: Wikimedia Commons/J Navas
How LEDs work. Photo: Wikimedia Commons/J Navas

If you read the last paragraph, I hope you agree with me that LEDs are cool.
So cool, in fact, that you might wonder if you could make them yourself. Well, no. It is much easier to buy them ready-to-go, as they are are cheap, but it’s still good to understand how they work.

Two very thin layers of a semiconducting matter, one that has a lot of electrons (N-type) and one that has very little electrons (P-type), called a PN­-junction, make up the basic structure. To create a PN­-junction, atoms of another material need to be added to the semiconducting material. This process is called doping (so don’t sign up your LEDs for the Olympics). The unique position of holes and electrons that move in the crystal lattice allows for the flow of current in only one direction. In all PN-junctions of the semiconductor part of the energy is emitted partly as heat and partly as photons. While in silicon and germanium most of the energy is emitted as heat and the light emitted is negligible, in other materials, as gallium arsenide phosphide (GaAsP) or gallium phosphide (GaP), the number of photons of luminous energy can create light strong enough to be efficient.

Depending on what kind of substrate is used to make the LED, the color of light can be different. The first diodes emitted only one color of light, but the ones used now have a broader spectrum, producing light that looks white. So let’s take a look at the history of these curious sources of light.

Shuji Nakamura and blue LEDs. Photo: Ladislav Markuš
Shuji Nakamura and blue LEDs. Photo: Ladislav Markuš

Electroluminescence was discovered in 1907 by H. J. Round, and the first LED was created in 1927 by Oleg Losev. At that time, LEDs could emit light from infrared to green wavelengths, but not the blue one.

In 2014, Shuji Nakamura, Isamu Akasaki and Hiroshi Amano were awarded the Nobel prize in physics for the invention of efficient blue light-emitting diodes. Finally, scientists had the domain of all the light spectrum, and the “white” LED became a reality. The blue LED does deserve the Nobel Prize, since it has enabled bright and energy-saving white light sources. Nakamura was also awarded the 2006 Millennium Technology Prize for his continuing efforts to make cheaper and more efficient light sources. As impactful as it sounds, LEDs are making the world much more smart, and now we are ready to see the details of how this happens.

Expensive vs. cheap LED arrays. Photo: Dave Dugdale (CC BY-SA)
Expensive vs. cheap LED arrays. Photo: Dave Dugdale (CC BY-SA)

From the manufacture point of view, many different kinds of metals and other elements need to be used to produce a LED. In the traditional light bulb, one has to use different kind of metals to produce light, therefore in this aspect both have disadvantages.
A traditional incandescent light bulb is often advertised as having a lifespan of 1,000 hours, while for CFL bulbs it is said to be up to 10,000 hours, which would translate to about 416 days of always-on burn time. For LEDs, that time is 50,000 hours, or about 2,083 days. Almost incomparable.

Furthermore, according to US Department of Energy testing of LED lamps from 2009, a typical 13-watt LED lamp emitted 450 to 650 lumens, the equivalent of a 40-watt incandescent bulb. The total cost of a LED lamp for 50,000 hours is $69.00, while for CFL bulbs it is $105.00, and $352.50 for incandescent ones. Considering that lighting consumes around 20% of all the electricity produced in the world, substituting all the light bulbs for 150 lm/Watt LED bulbs would save 10% of all the electricity produced. That is the equivalent of 2,000 TWh, which is the same as 250 nuclear reactors.

The new manufacturing techniques have also brought down the cost of LEDs, and now they are widely used in households all over the world as a highly efficient source of light. In combination with other renewable energy sources, LEDs have all the potential to save the planet, and it up to us to take advantage of these technology and move towards a green ever after future. Right now, I’m enjoying the lighting from my LED light bulb while I feel that I’m contributing to the planet. Have you bought yours yet?

Further Reading
All About Circuits: Electrons and holes

Vitória Barim Pacela is a Millennium Youth Camp alumna studying at the University of Helsinki and an undergraduate researcher at the Accelerator Laboratory. She is passionate about science, technology and sustainable development.