LED – Light Beyond Compare

Christmas streets in Helsinki were lit by nearly 170,000 LED lights in 2015. The energy saving compared to electric bulbs is a huge 85 percent.
Photo: Jussi Hellsten / Visit Helsinki.

LED lights have become a mass product from ten years ago when the innovation that led to their development won the Millennium Technology Prize. As LEDs remain far from their maximum output rating, the future looks bright indeed.

Visitors to Helsinki last Christmas were treated to the sight of street decorations twinkling to the tune of nearly 170,000 LED lights. Christmas streets of the Finnish capital are a prime example of the proliferation of LEDs in lighting in recent years. The reason: LEDs are superior both in terms of lifetime and energy efficiency.

LED technology has taken huge leaps forward since Japanese Shuji Nakamura’s innovation of a blue and white LED light was awarded the Millennium Technology Prize in 2006. LEDs give us more and higher-quality light at clearly lower cost. Improvements in efficiency have brought prices down, and in ten years LEDs have moved from specialized applications to the mass market.

“Each year new LEDs are about ten percent more efficient than the previous ones.”

“Each year new LEDs are introduced to the market which are about ten percent more efficient than the previous ones,” says staff scientist Sami Suihkonen from Aalto University Department of Micro and Nanosciences.

One important step has been the achievement of a warmer colour tone.

“The coldness of early LED lights put off consumers in the West, unlike in Asia, for example. Today the colour can be made very warm indeed, but ten years ago the main consumer LED applications were flash lights with a pale cold white beam”, Suihkonen compares the past with the present.

It was precisely the development of the lights’ tone that made Helsinki replace old-fashioned light bulbs with a few thousand LEDs for the Christmas decorations in Aleksanterinkatu thoroughfare in 2009.

“We had looked into the possibility of using LEDs before, but we only accepted them when we could have lights with the same tone as old light bulbs. For the 2015 Christmas decorations we had no trouble finding 160,000 suitable LEDs for the entire Esplanadi park,” says Riitta Lassander, Executive Director at Helsinki City Marketing.

The switchover to LEDs carries environmental benefits as well: the energy consumption of Christmas lights in Helsinki dropped to one fifth from what it used to be.

Staff scientist Sami Suihkonen from Aalto University specialises in LED materials. He regularly collaborates with the Millennium Prize winning inventor of the LED light. Photo: Laura Manas / TAF

 

Responsibility for product development rests with companies

LED or Light Emitting Diode is a semiconductor component that thanks to its layered structure emits coloured light when electric current passes through. Sami Suihkonen from Aalto University is a leading semiconductor material researcher in Finland. Three years ago he worked in the research team under Millennium Prize winner Nakamura at University of California, Santa Barbara, and he still keeps in touch with the team on a weekly basis.

Since Nakamura won the award, much of the development of existing types of commercial LEDs has been taken over by private companies. The UC Solid State Lighting and Energy Center led by Nakamura SSLEEC is also funded almost entirely by corporations.

“The process chain in LED production is so long that the most efficient LEDs can only be produced by companies, not universities. Large industrial reactors can make the necessary materials for hundreds of thousands of LEDs at one go,” Suihkonen says.

The technology for the manufacture of commercial LEDs is nevertheless the same that Nakamura and his research colleagues Isamu Akasaki and Hiroshi Amano used 30 years ago in their breakthrough. Companies use the same technology but utilize several different platforms and focus on their optimization.

“None of the production platforms the companies use has proved yet to be superior and the competition is intense. However, there is little scientific novelty involved with the production chain development itself,” says Suihkonen.

Full efficiency still to come

Companies have their work cut out for them, because consumer LEDs are nowhere near their maximum theoretical efficiency. LEDs yield more light per unit of area than fluorescent tubes or incandescent bulbs, but their manufacture is still expensive compared to the quality of their light and their energy efficiency.

“A few decades from now all new lights will be LEDs.”

“Nakamura, Akasaki and Amano won the 2014 Nobel Prize for showing in the 1990s that LED materials could be manufactured with at least satisfactory quality – that at least some light could be produced from the diodes. Scientifically, however, the diode material is still full of crystalline defects and far from ideal,” Suihkonen explains.

Current LED lights compete with fluorescent tubes in terms of their energy efficiency, but the price of LEDs is about five times higher. For example, the 160,000 plus LED lights in Helsinki cost 200,000 euro fully installed.

Because of overhaul costs, LED lights have not yet taken over streets and shops or large public spaces. High-quality LEDs can today compete with fluorescent lights only with their superior lifetime, which means considerably smaller service needs.

The present shortcoming of LEDs will in the future be their greatest competitive asset, however. According to Suihkonen, the efficiency of the electric bulb and the fluorescent tube have been taken “as far as nature allows,” but the limit imposed by physics on LEDs is still far away. In the laboratory, LEDs are already vastly more energy efficient than other types of light sources.

“A few decades from now all new lights will probably be LEDs,” Suihkonen believes.

The Esplanadi park in Helsinki was lit by nearly 170,000 LED lights for Christmas 2015.
Photo: Sylvain Manas.

 

Towards a green LED and water purification

Universities may play a decisive role in the improvement of the efficiency of LEDs. Where companies refine existing technologies, universities study new structures, materials and methods to improve LEDs.

Because the manufacturing cost of LEDs varies with the surface area of the diode, better materials can potentially lower the cost of LEDs to a fraction of their current price. A bright white LED is today produced by adding a coating of phosphor over a blue LED, which turns part of the blue light into red and yellow. The combination has the appearance of white light, but because of the phosphor some of the light is lost and the efficiency is thereby decreased.

One answer to the dilemma could be to combine a green LED with a blue and a red one, rendering phosphor unnecessary. Manufacturing methods for green LED are currently under development in Aalto University and other places, but according to Suihkonen it remains the weak link in the process.

“We have many ideas for developing a green LED and we know the materials that can be made to emit green light, but the efficiency is still far from what is needed in practical lighting applications.”

While the light emitting properties of LEDs are refined, entirely new applications for LEDs are also being developed. For instance, Nakamura’s technique is today used to make water purification equipment. Short wavelength ultraviolet LEDs can be used to kill bacteria, and there are already battery-operated water purification pens for consumers.

Purification of water with LED light has been studied in Finnish universities as well, but the technique is not yet ready for commercial exploitation.

“There are still great challenges in material manufacturing techniques and efficiency. We need a new Nakamura to develop a viable production method,” Suihkonen chuckles.

Text: Laura Manas

The 2016 Millennium Technology Prize will be awarded on 24 May 2016 in Helsinki.

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