Quantum dots offer efficient, colour accurate alternative to LEDs

Developed by University of Cambridge researchers, the quantum dots are formed from tiny semiconductors just a few billionths of a metre in size and were created using a combination of nanotechnology, colour science, advanced computational methods, electronics and a unique fabrication process.

The team found that by using more than the three primary lighting colours, the system 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.

With the amount of ambient light often 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, because of their high colour tunability and colour purity. Due to their unique optoelectronic properties, they show excellent colour performance in both wide colour controllability and high colour rendering capability.

The Cambridge researchers developed an architecture for next-generation smart white lighting based on quantum-dot light-emitting diodes (QD-LED). The 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.

The QD-LED system was able to output a much broader colour temperature (CCT) range than current LED-based smart lights.

The 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.

Professor Jong Min Kim, who co-led the research, said: “This is the first milestone toward the full exploitation of quantum-dot-based smart white lighting for daily applications.”