̽��ֱ�� of Cambridge - lighting

Smart lighting system based on quantum dots more accurately reproduces daylight

sc604 — Wed, 03 Aug 2022 09:00:00 +0000

̽��ֱ��researchers, from the ̽��ֱ�� of Cambridge, designed the next-generation smart lighting system using a combination of nanotechnology, colour science, advanced computational methods, electronics and a unique fabrication process.

̽��ֱ��team found that by using more than the three primary lighting colours used in typical LEDs, they were able to reproduce daylight more accurately. Early tests of the new design showed excellent colour rendering, a wider operating range than current smart lighting technology, and wider spectrum of white light customisation. ̽��ֱ��results are reported in the journal Nature Communications.

As the availability and characteristics of ambient light are connected with wellbeing, the widespread availability of smart lighting systems can have a positive effect on human health since these systems can respond to individual mood. Smart lighting can also respond to circadian rhythms, which regulate the daily sleep-wake cycle, so that light is reddish-white in the morning and evening, and bluish-white during the day.

When a room has sufficient natural or artificial light, good glare control, and views of the outdoors, it is said to have good levels of visual comfort. In indoor environments under artificial light, visual comfort depends on how accurately colours are rendered. Since the colour of objects is determined by illumination, smart white lighting needs to be able to accurately express the colour of surrounding objects. Current technology achieves this by using three different colours of light simultaneously.

Quantum dots have been studied and developed as light sources since the 1990s, due to their high colour tunability and colour purity. Due their unique optoelectronic properties, they show excellent colour performance in both wide colour controllability and high colour rendering capability.

̽��ֱ��Cambridge researchers developed an architecture for quantum-dot light-emitting diodes (QD-LED) based next-generation smart white lighting. They combined system-level colour optimisation, device-level optoelectronic simulation, and material-level parameter extraction.

̽��ֱ��researchers produced a computational design framework from a colour optimisation algorithm used for neural networks in machine learning, together with a new method for charge transport and light emission modelling.

̽��ֱ��QD-LED system uses multiple primary colours – beyond the commonly used red, green and blue – to more accurately mimic white light. By choosing quantum dots of a specific size – between three and 30 nanometres in diameter – the researchers were able to overcome some of the practical limitations of LEDs and achieve the emission wavelengths they needed to test their predictions.

̽��ֱ��team then validated their design by creating a new device architecture of QD-LED based white lighting. ̽��ֱ��test showed excellent colour rendering, a wider operating range than current technology, and a wide spectrum of white light shade customisation.

̽��ֱ��Cambridge-developed QD-LED system showed a correlated colour temperature (CCT) range from 2243K (reddish) to 9207K (bright midday sun), compared with current LED-based smart lights which have a CCT between 2200K and 6500K. ̽��ֱ��colour rendering index (CRI) – a measure of colours illuminated by the light in comparison to daylight (CRI=100) – of the QD-LED system was 97, compared to current smart bulb ranges, which are between 80 and 91.

̽��ֱ��design could pave the way to more efficient, more accurate smart lighting. In an LED smart bulb, the three LEDs must be controlled individually to achieve a given colour. In the QD-LED system, all the quantum dots are driven by a single common control voltage to achieve the full colour temperature range.

“This is a world-first: a fully optimised, high-performance quantum-dot-based smart white lighting system,” said Professor Jong Min Kim from Cambridge’s Department of Engineering, who co-led the research. “This is the first milestone toward the full exploitation of quantum-dot-based smart white lighting for daily applications.”

“ ̽��ֱ��ability to better reproduce daylight through its varying colour spectrum dynamically in a single light is what we aimed for,” said Professor Gehan Amaratunga, who co-led the research. “We achieved it in a new way through using quantum dots. This research opens the way for a wide variety of new human responsive lighting environments.”

̽��ֱ��structure of the QD-LED white lighting developed by the Cambridge team is scalable to large area lighting surfaces, as it is made with a printing process and its control and drive is similar to that in a display. With standard point source LEDs requiring individual control this is a more complex task.

̽��ֱ��research was supported in part by the European Union and the Engineering and Physical Sciences Research Council (EPSRC), part of UK Research and Innovation (UKRI).

Reference:
Chatura Samarakoon et al. ‘Optoelectronic System and Device Integration for Quantum-Dot Light-Emitting Diode White Lighting with Computational Design Framework.’ Nature Communications (2022). DOI: 10.1038/s41467-022-31853-9

Researchers have designed smart, colour-controllable white light devices from quantum dots – tiny semiconductors just a few billionths of a metre in size – which are more efficient and have better colour saturation than standard LEDs, and can dynamically reproduce daylight conditions in a single light.

This research opens the way for a wide variety of new human-responsive lighting environments

Gehan Amaratunga

Yaorusheng via Getty Images

Long exposure light painting

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Atom swapping could lead to ultra-bright, flexible next generation LEDs

sc604 — Mon, 07 Jun 2021 15:25:23 +0000

̽��ֱ��researchers, led by the ̽��ֱ�� of Cambridge and the Technical ̽��ֱ�� of Munich, found that by swapping one out of every 1,000 atoms of one material for another, they were able to triple the luminescence of a new material class of light emitters known as halide perovskites.

This ‘atom swapping’, or doping, causes the charge carriers to get stuck in a specific part of the material’s crystal structure, where they recombine and emit light. ̽��ֱ��results, reported in the Journal of the American Chemical Society, could be useful for low-cost printable and flexible LED lighting, displays for smartphones or cheap lasers.

Many everyday applications now use light-emitting devices (LEDs), such as domestic and commercial lighting, TV screens, smartphones and laptops. ̽��ֱ��main advantage of LEDs is they consume far less energy than older technologies.

Ultimately, also the entirety of our worldwide communication via the internet is driven by optical signals from very bright light sources that within optical fibres carry information at the speed of light across the globe.

̽��ֱ��team studied a new class of semiconductors called halide perovskites in the form of nanocrystals which measure only about a ten-thousandth of the thickness of a human hair. These ‘quantum dots’ are highly luminescent materials: the first high-brilliance QLED TVs incorporating quantum dots recently came onto the market.

̽��ֱ��Cambridge researchers, working with Daniel Congreve’s group at Harvard, who are experts in the fabrication of quantum dots, have now greatly improved the light emission from these nanocrystals. They substituted one out of every one thousand atoms with another – swapping lead for manganese ions – and found the luminescence of the quantum dots tripled.

A detailed investigation using laser spectroscopy revealed the origin of this observation. “We found that the charges collect together in the regions of the crystals that we doped,” said Sascha Feldmann from Cambridge’s Cavendish Laboratory, the study’s first author. “Once localised, those energetic charges can meet each other and recombine to emit light in a very efficient manner.”

“We hope this fascinating discovery: that even smallest changes to the chemical composition can greatly enhance the material properties, will pave the way to cheap and ultrabright LED displays and lasers in the near future,” said senior author Felix Deschler, who is jointly affiliated at the Cavendish and the Walter Schottky Institute at the Technical ̽��ֱ�� of Munich.

In the future, the researchers hope to identify even more efficient dopants which will help make these advanced light technologies accessible to every part of the world.

Reference:
Sascha Feldmann et al. ‘Charge carrier localization in doped perovskite nanocrystals enhances radiative recombination.’, Journal of the American Chemical Society (2021). DOI: 10.1021/jacs.1c01567

An international group of researchers has developed a new technique that could be used to make more efficient low-cost light-emitting materials that are flexible and can be printed using ink-jet techniques.

Ella Maru Studio

Artist’s impression of glowing halide perovskite nanocrystals

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Lighting for the 21st century

bjb42 — Sat, 01 Aug 2009 14:41:07 +0000

A revolution in lighting is under way. Thanks to advances in the technology, efficiency and cost of light-emitting diodes (LEDs), these devices are ready to take over in the very near future from conventional forms of incandescent lighting. ̽��ֱ��potential energy savings are huge: statistics from the US Department of Energy estimate that, by 2025, solid-state lighting such as LEDs could reduce the global amount of electricity used for lighting by 50% and, in the US alone, could eliminate 258 million metric tons of carbon emission, alleviate the need for 133 new power stations, and result in cumulative financial savings of over a hundred billion dollars. At the forefront of research underpinning this new lighting paradigm is a focus on the semiconductor gallium nitride (GaN) at the Cambridge Centre for Gallium Nitride in the Department of Materials Science and Metallurgy.

Why use GaN for LEDs?

LEDs based on GaN, which emits brilliant light when electricity is passed through it, are extremely energy efficient and long lasting. Traditional incandescent light bulbs are only 5% efficient at converting the electricity they consume into light, and, although low-energy light bulbs are 20% efficient, they contain hazardous mercury. Compare this with white GaN LEDs, which are already 30% efficient and have a target efficiency of 60%. GaN LEDs are also incredibly long lasting: an LED can burn for 100,000 hours. In practical terms, this means it only needs replacing after 60 years of typical household use.

In the UK, lighting consumes over a fifth of all the electricity generated at power stations, and GaN LEDs have the potential to reduce this figure by at least 50% and possibly by 75%.

̽��ֱ��Holy Grail for GaN is home and office lighting. Research directed at reducing manufacturing costs and improving the quality of light is bringing this goal closer.

Materials and devices

Research at the Cambridge Centre for Gallium Nitride, directed by Professor Colin Humphreys, the Director of Research in the Department of Materials Science and Metallurgy, stretches from fundamental materials studies through to applications and devices.

̽��ֱ��Centre has world-class GaN growth and characterisation facilities and has recently developed an innovative technique for growing GaN on large silicon wafers, instead of the more expensive sapphire wafers; this could deliver a tenfold reduction in LED manufacturing costs. ̽��ֱ��Centre is also working on improving the quality of light by coating blue LEDs with phosphors to produce white light. This will be improved still further through the use of novel phosphors produced by Professor Tony Cheetham in the Department of Materials Science and Metallurgy.

̽��ֱ��future

GaN LEDs have hit the market rapidly and are already widely used in flashlights and front bicycle lights, as backlighting for mobile phones and interior lighting in cars and aeroplanes, and even to light up landmarks such as the façade of Buckingham Palace and the length of the Severn Bridge. Looking ahead, the timescale for the widespread adoption of GaN LEDs in homes and offices is probably as short as 5–10 years.

Other applications also look promising. Research at the Centre is investigating the possibility of using GaN LEDs to mimic sunlight, which could have important benefits for sufferers of seasonal affective disorder (SAD). And other studies are investigating how UV LEDs, created by adding aluminium to GaN, could be used for killing bacteria and stopping viruses from reproducing, either to purify water in the developing world or to ‘sweep’ hospital wards to eradicate superbugs.

For more information, please contact the author Professor Colin Humphreys (colin.humphreys@msm.cam.ac.uk) at the Cambridge Centre for Gallium Nitride. ̽��ֱ��Centre’s research is funded by the Engineering and Physical Sciences Research Council (EPSRC), the Technology Strategy Board (TSB), Aixtron Ltd, Sharp Electronics Europe, QinetiQ, Forge Europa, Philips, Imago Scientific Instruments and RFMD (UK) Ltd, and is performed in collaboration with the ̽��ֱ�� of Manchester and Sheffield Hallam ̽��ֱ��.

A remarkable light-emitting material, gallium nitride, could slash electricity consumption, purify water and kill superbugs.

In the UK, lighting consumes over a fifth of all the electricity generated at power stations, and GaN LEDs have the potential to reduce this figure by at least 50% and possibly by 75%.

Colin Humphreys

Green LEDs

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