Researchers have designed controllable color white light smart devices from quantum dots (tiny semiconductors a few billionths of a meter) that are more efficient and have better color saturation than standard LEDs, and can dynamically reproduce conditions of daylight in a single light
The researchers, from the University of Cambridge, designed the next-generation smart lighting system using a combination of nanotechnology, color science, advanced computational methods, electronics and a unique manufacturing process.
The team found that by using more of the three primary lighting colors used in typical LEDs, they were able to more accurately reproduce daylight. Early tests of the new design showed excellent color rendering, a wider operating range than current smart lighting technology, and a broader spectrum of white light customization. The results are published in the journal nature communications.
If the availability and characteristics of ambient light are related to well-being, the widespread availability of smart lighting systems can have a positive effect on human health, as these systems can respond to individual mood. Smart lighting can also respond to circadian rhythms, which regulate the daily sleep-wake cycle, so 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 to the outside, it is said to have good levels of visual comfort. In indoor environments under artificial light, visual comfort depends on the accuracy with which colors are represented. Since the color of objects is determined by lighting, smart white lighting must be able to accurately express the color of surrounding objects. Current technology accomplishes this by using three different colors of light simultaneously.
Quantum dots have been studied and developed as light sources since the 1990s, due to their high tuning ability and color purity. Due to their unique optoelectronic properties, they exhibit excellent color performance in both wide color controllability and high color rendering ability.
Cambridge researchers developed an architecture for quantum dot light-emitting diodes (QD-LEDs) based on next-generation smart white lighting. They combined system-level color optimization, device-level optoelectronic simulation, and material-level parameter extraction.
The researchers produced a computational design framework from a color optimization algorithm used for neural networks in machine learning, 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 accurately 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 QD-LED-based white light fixture architecture. The test showed excellent color rendering, a wider operating range than current technology, and a broad spectrum of white light tone customization.
The Cambridge-developed QD-LED system showed a correlated color temperature (CCT) range of 2243K (reddish) to 9207K (bright midday sun), compared to current LED-based smart lights that 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 the ranges of smart light bulbs, which are between 80 and 91 .
The design could pave the way to more efficient and precise smart lighting. In a smart LED bulb, all three LEDs must be individually controlled to achieve a certain color. In the QD-LED system, all quantum dots are controlled 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 Cambridge Department of Engineering, who co-led the research. “This is the first milestone towards fully exploiting quantum dot-based smart white lighting for everyday applications.”
“The ability to better reproduce daylight through its dynamically varying color spectrum in a single light is what we are after,” said Professor Gehan Amaratunga, who co-led the research. “We achieve this in a new way by using quantum dots. This research paves the way for a wide variety of new human-sensitive lighting environments.”
The structure of the QD-LED white lighting developed by the Cambridge team is scalable to large-area lighting surfaces, since it is made with a printing process and its control and operation is similar to that of a display. With standard point source LEDs requiring individual control, this is a more complex task.
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).