Researchers have developed smart, color-controllable white-light devices made from quantum dots — tiny semiconductors just a few billionths of a meter in size — that are more efficient and have better color saturation than standard LEDs, and can dynamically reproduce daylight conditions in a single light.
University of Cambridge researchers designed the next-generation intelligent lighting system using a combination of nanotechnology, color science, advanced computing methods, electronics and a unique manufacturing process.
The team found that by using more than the three primary illumination colors used in typical LEDs, they were able to more accurately reproduce daylight. Early testing of the new design showed excellent color reproduction, a wider operating range than current smart lighting technology, and a wider range of white light adjustments. The results are published in the journal today (3 August). nature communication.
Since the availability and properties of ambient light are linked to well-being, the widespread availability of intelligent lighting systems can have a positive impact on human health, as these systems can react to individual moods. Smart lighting can also respond to circadian rhythms that regulate daily sleep-wake cycles, so light is reddish-white in the morning and evening and bluish-white during the day.
If a room has sufficient natural or artificial light, good glare control and a view of the outside, it is said to have good visual comfort. In indoor environments with artificial light, visual comfort depends on how accurately colors are rendered. Since the color of objects is determined by lighting, smart white lighting must be able to accurately reproduce the color of surrounding objects. Current technology achieves this by using three different colors of light at the same time.
Quantum dots have been studied and developed as light sources since the 1990s because of their high color tunability and color purity. Due to their unique optoelectronic properties, they show excellent color performance in terms of both broad color controllability and high color rendering ability.
Cambridge researchers developed an architecture for quantum dots-based light-emitting diodes (QD-LEDs) for the next generation of smart white lighting. They combined system-level color optimization, device-level optoelectronic simulation, and material-level parameter extraction.
Researchers created a computational design framework from a color optimization algorithm used for machine learning neural networks, along with a new method for charge transport and light emission modelling.
The QD-LED system uses multiple primary colors – beyond the commonly used red, green and blue – to more closely mimic white light. By choosing quantum dots of a specific size – between three and 30 nanometers 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 team then validated their design by creating a new device architecture with QD-LED-based white illumination. The test demonstrated excellent color reproduction, a wider operating range than current technology, and a wide range of white light tone customization options.
The Cambridge-developed QD-LED system showed a correlated color temperature range (CCT) from 2243K (reddish) to 9207K (bright midday sun), compared to current LED-based smart lights, which have a CCT between 2200K and 6500K. The color rendering index (CRI) – a measure of the colors illuminated by light compared to daylight (CRI = 100) – of the QD-LED system was 97, compared to current smart bulb ranges which are between 80 and 91.
The design could pave the way to more efficient and accurate smart lighting. In a smart LED light bulb, the three LEDs must be controlled individually to achieve a specific color. In the QD-LED system, all quantum dots are driven by a single common control voltage to achieve the full color temperature range.
“This is a world first: a fully optimized high-performance quantum dot-based smart white lighting system,” said Professor Jong Min Kim of the Department of Engineering in Cambridge, who co-led the research. “This is the first milestone towards full utilization of quantum dot-based smart white lighting for everyday applications.”
“The ability to better reproduce daylight dynamically in a single light through its varying spectrum of colors is our goal,” said Professor Gehan Amaratunga, who co-led the research. “We achieved it in a new way by using quantum dots. This research paves the way for a variety of new human-responsive lighting environments.”
The structure of the QD-LED white illumination developed by the Cambridge team is scalable to large-area luminous areas because it is manufactured using a printing process and its control and activation is similar to a display. For standard point source LEDs that require individual control, this is a more complex task.
Reference: “Optoelectronic System and Device Integration for Quantum-Dot Light-Emitting Diode White Lighting with Computational Design Framework” August 3, 2022, nature communication.
The 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).