Researchers have designed smart, color-controlled white-light devices from quantum dots — semiconductors as small as a few billionths of a meter — that are more efficient, have better color saturation than standard LEDs, and can dynamically reproduce daylight conditions in a single light.
The researchers, from the University of Cambridge, have designed a 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 than three primary light colors used in typical LEDs, they were able to more accurately reproduce daylight. Early tests of the new design showed great color rendering, a wider operating range than current smart lighting technology, and a wide range of white light customization. The results were reported in the journal Nature Communications.
If the availability and characteristics of ambient lighting are related to well-being, then the wide availability of smart lighting systems can have a positive impact on human health because these systems can respond to individual moods. Smart lighting can also respond to circadian rhythms, which regulate the daily sleep-wake cycle, so that the 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 the colors are displayed. Since the color of objects is determined by lighting, intelligent white lighting must be able to accurately express the color of surrounding objects. Current technology achieves 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 color tunability and color purity. Due to its unique optoelectronic properties, it shows excellent color performance in both wide color controllability and high color rendering ability.
Cambridge researchers have developed an architecture for quantum dot light emitting diodes (QD-LEDs) based on the next generation of smart white lighting. They have integrated system-level color optimization, device-level optoelectronic simulation, and material-level parameter extraction.
The researchers produced a computational design framework from the color optimization algorithm used in neural networks in machine learning, along with a new method for charge transfer and light emission modeling.
The QD-LED system uses multiple primary colors – other than the commonly used red, green, and blue – to more accurately mimic white light. By choosing quantum dots of a specific size — with a diameter of between three and 30 nanometers — 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-lighting device architecture. Testing showed excellent color rendering, a wider operating range than current technology, and a wide spectrum of white light shade customization.
The Cambridge-developed QD-LED system demonstrated a correlated color temperature (CCT) range of 2,243 K (reddish) to 9207 K (bright midday sun), compared to current LED-based smart lights with a color temperature of 2,200 K and 6500 kelvin. The color rendering index (CRI) – a measure of color in light compared to daylight (CRI = 100) – for the QD-LED system was 97, compared to current smart bulb ranges, which range from 80 to 91.
The design could pave the way for more efficient and accurate smart lighting. In a smart LED bulb, the three LEDs must be controlled individually to achieve a specific color. In a QD-LED system, all quantum dots are powered by a single common control voltage to achieve the full color temperature range.
“This is a world first: an improved, high-performance intelligent white-lighting system based on quantum dots,” said Professor Jung Min Kim from Cambridge’s Department of Engineering, who co-led the research. “This is the first milestone toward fully exploiting quantum dot-based smart white lighting for everyday applications.”
“The ability to better reproduce daylight with a dynamically varied color spectrum in a single light is what we’re aiming for,” said Professor Jehan Amaratunga, who co-led the research. “We’ve achieved this in a new way through the use of quantum dots. This research opens the way to a variety of new human-responsive lighting environments.”
The QD-LED white light architecture developed by the Cambridge team is scalable on large-area lighting surfaces, as it is made with a printing process, controlled and actuated similar to that of a screen. With point source LEDs that require individual control, this is a much more complicated 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).