By using quantum dots – tiny semiconductors measuring just a few billionths of a meter – the researchers have designed intelligent, color-controlled white light devices that are more efficient, better color saturation and can dynamically reproduce daylight conditions in a single light compared to standard LEDs.
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Researchers from the University of Cambridge have used a combination of nanotechnology, color science, advanced computational methods, electronics and unique manufacturing processes to design the next generation of smart lighting systems.
The team found that by using more than the three main lighting colors used in typical LEDs, they were able to reproduce daylight more accurately. Early tests of the new design showed excellent color rendering with a broader operating range and a broader customized spectrum of white light than current smart lighting technologies. These results have been published recently in Nature Communications.
Because the availability and properties of ambient light are health-related, the spread of smart lighting systems can have a positive impact on human health because they can respond to individual emotions. In addition, smart lighting can respond to circadian rhythms and regulate the daily sleep-wake cycle, so that light is red-white in the morning and evening, and blue-white during the day.
When a room has enough natural or artificial light, good glare control and a view of the outdoors, then it is said to have good visual comfort. In an indoor environment with artificial light, visual comfort depends on how accurately colors are rendered. Since the color of an object is determined by illumination, intelligent white lighting needs to be able to accurately represent the color of surrounding objects. Current technology achieves this by using three different colors of light at the same time.
Because of their high color tunability and color purity, quantum dots have been studied and developed as light sources since the 1990s. Due to their unique optoelectronic properties, they exhibit excellent color performance in terms of both broad color tractability and high color rendering.
Researchers at the University of Cambridge have developed an architecture for next-generation smart white lighting based on quantum dot light-emitting diodes (QD-LEDs). They combined system-level color optimization, device-level optoelectronic simulation and material-level parameter extraction.
The researchers generated a computational design framework from a color optimization algorithm used in machine learning for neural networks, along with a new approach for charge transport and light emission modeling.
The QD-LED system uses multiple primary colors – beyond the commonly used red, green and blue – to more accurately model white light. By selecting quantum dots of a specific size – between 3 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 for white lighting based on QD-LEDs. The test results showed excellent color rendering, which has a wider operating range than current technology and a wide spectrum of white light shade customization.
The QD-LED system developed at Cambridge University shows a relevant color temperature (CCT) range from 2243 K (reddish) to 9207 K (bright midday sun), while current LED-based smart lights have CCTs between 2200 K and 6500 K. The color rendering index (CRI) of the QD-LED system – a measure of the color illuminated by the light compared to daylight (CRI=100) -is 97, while current smart bulbs range between 80 and 91.
The design could pave the way for more efficient and accurate smart lighting. In an LED smart 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 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 University of Cambridge’s Department of Engineering. This is the first milestone in the full exploitation of quantum dot-based smart white lighting for everyday applications.”
Professor Gehan Amaratunga, who co-led the research, said, “The ability to better reproduce daylight dynamically through its different color spectra in a single lamp is our goal. We have achieved this in a new way by using quantum dots. This research opens the way for a variety of new human-responsive lighting environments.”
The structure of the QD-LED white illumination developed by the Cambridge team can be extended to illuminate large surfaces due to the fact that it is made using a printing process with controls and drivers similar to those found in displays. This is a more complex task because standard point source LEDs need to be controlled individually.
