Move over Alexa, These Smart Lights Don’t Need You to Tell Them When to Shine

New research published in Optical Engineering figures out how to keep temperature changes and age-based deterioration from impacting an LED light emission's strength, consistency, and color.

04 April 2019

The role that light plays in regulating the 24-hour circadian rhythm is well understood by scientists, and so broadly accepted by the mainstream population that there is increasing commercial demand for more human-centric lighting in residences and offices.

Human-centric lighting (HCL) can be used to create dynamic indoor environments that mimic daylight patterns with respect to human circadian rhythms and physiology. For example, the stimulating effects of bluer frequencies are welcome during daytime hours, whereas amber and red frequencies are relaxing, and therefore more desirable in the evenings. HCL is enabled by the maturity of LED lighting, which enables finely tuned control over the color temperature of the light, as well as spectral power and brightness.

In addition to enhancing our sleep and wellbeing, solid-state lighting benefits are evident in the ongoing development of applications in medicine, imaging, agriculture, communication, transportation, and museum lighting. Some of these applications require highly precise light spectra that don't produce optical power variations or shifts in color over time.

But as a bulb ages or a junction heats up, the spectral distributions fluctuate. The amber spectrum may weaken before the blue spectrum. But wouldn't it be great if a bulb could recognize, by itself, that its amber channel was fading? And if, after recognizing this fact, it could increase the pulse-width modulation weight of the amber channel so that it continues to meet the spectral power distribution required for a specific setting?

Researchers Aleix Llenas from Catalonia Institute for Energy Research (Spain) and Josep Carreras from Ledmotive Technologies (Spain) have done just that. Their work, recently published in the SPIE journal Optical Engineering, addresses two lighting challenges: how to keep temperature changes and age-based deterioration from impacting a light emission's strength, consistency, and color, as well as providing a reliable, internal, self-monitoring method.

They use a fast-computation annealing algorithm to determine channel weights of a targeted SPD, such as one designed for optimal lighting at 5 p.m. In conjunction, a microprocessor in the light provides a closed-loop control system that monitors and corrects the spectral output, compensating for shifts due to temperature changes or wear and tear on the LED. In effect, the light can keep an emitted spectrum constant and stable over time.

Daniel LeMaster, associate editor for Optical Engineering, believes that the research showcases significant advances in terms of lighting technologies. He says, "This method to monitor and quickly compensate for the colorimetric issues that arise from junction heating and LED aging will be of great utility in the global LED lighting market."

The intelligence and spectral awareness of these LEDs create new possibilities for healthier living spaces by giving lighting designers complete control over the visible spectrum, at any time of day.

Read the original article online: Llenas and Carreras, "Arbitrary spectral matching using multi-LED lighting systems," Opt. Eng. 58(3), 035105 (2019).

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