Multi-channel SSL system enhances health and wellbeing in residential retrofit - Part 1 (MAGAZINE)

April 23, 2018
Tunable lighting and programmatic controls can deliver a natural-light experience in a residential setting that enhances human wellbeing. In Part 1 of a series, Maury Wright explains the human-centric lighting technology deployed in an actual home remodel for a resident that suffers from heightened sensitivity to light and sleep issues.

Tunable lighting and programmatic controls can deliver a natural-light experience in a residential setting that enhances human wellbeing. In Part 1 of a series, MAURY WRIGHT explains the technology deployed in an actual home remodel for a resident that suffers from heightened sensitivity to light and sleep issues.

The concept of lighting for health and wellbeing or human-centric lighting holds great promise to positively impact people in terms of enhanced productivity, more restful sleep, faster healing, general wellness, and more. Indeed, differing spectral power distribution (SPD) and CCT can both please or disrupt the human visual system, and impact physiology through non-visual receptors. While researchers and manufacturers are still studying the science behind such lighting and the effects of different SPDs and light levels on humans, it’s increasingly clear that tunable LED-based systems have a bright future. LEDs Magazine was able to chronicle firsthand the installation of such a lighting system from Ketra during a major home remodel project. In this first article of a series, we will examine the science behind the project and the solid-state lighting (SSL) and controls installed. A follow-on article will detail the results and the impact on the homeowner living with the new lighting every day.

FIG. 1. A control panel in a dining area allows an occupant to simply change scenes, while programmatic controls can automatically set the light environment as well based on time of day, and day of year.

We have written about lighting for health and wellbeing or human-centric lighting extensively. Still, we acknowledge that the lighting industry lacks conclusive medical evidence that documents a positive impact on people. There are certainly plenty of case studies that associate a positive outcome with the use of tunable lighting delivering cooler light with more blue spectral energy early in the day, and warmer light with less blue energy in the evening. For background on the topic, you might peruse the commercial-office lighting installation we wrote about late last year. It appears that the lighting industry is feeling more comfortable in experimenting with tunable lighting aimed at wellbeing. But we will always advocate for caution as well, and indeed one of the lighting designers behind the project mentioned before has advocated for caution in our pages.

Science of lighting and health

Indeed, there is no precise science when it comes to optimal light recipes for health. The subject of light exposure relative to SPD, dose, time, space, and more is being constantly studied. Even the subject of metrics for characterizing the impact of light on the nonvisual system remains contentious, with reputable researchers championing different concepts.

The two prevalent metrics are melanopic lux and circadian stimulus (CS). Melanopic lux is similar to the standard lux metric, except that the former is defined relative to the nonvisual intrinsically photosensitive retinal ganglion cells (ipRGCs), while the latter is defined relative to the rods and cones and the accepted spectral band of the human visual system. We will provide more details on CS, but it is a metric intended to quantify the effectiveness of a light source in activating the circadian system.

The details of that metric debate are beyond our scope here. Both have some viability and have smart people behind them. But here we will focus on CS because that’s the basis of the programmatic tunability of Ketra’s SSL platform and was developed by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute. The LRC is one of the foremost organizations researching lighting for health. Mariana Figueiro is the current LRC director and the longtime leader of the Light and Health Program at the LRC, and Ketra is one of the members of the program’s Light and Health Alliance.

FIG. 2. Replacement lamps include the company’s tunable A-lamp (inset) and a directional lamp installed in a traditional recessed housing (main).

In her research, Figueiro relies on measuring the spectral irradiance distribution of light at the cornea and correlating that distribution to measured melatonin suppression. Gathering data over scores of tests enabled Figueiro and her team to develop a calculated value of circadian light, which is weighted to the spectral sensitivity of the circadian system based on a one-hour exposure to the light. CS is then calculated as a fractional value expressing the effectiveness of the light in impacting the circadian system. The LRC even offers a CS calculator for free download and updated that calculator in October 2017. Furthermore, Figueiro’s research can guide lighting specification as to appropriate CS values over the course of the day.

Ketra bases its control strategy on the LRC work and the CS metric. Tom Hamilton, vice president of solutions and services at Ketra, said, "We take the LRC work and translate the experience that can be deployed into the built environment." The result is an SSL system that delivers constantly-changing intensity and SPD based on the time of day and LRC dosage concepts — and even changes in spatial elements such as the position of the apparent light source in space enabled by layering of light.

Scenes and spaces

Working from the CS baseline, Ketra approaches different areas of a commercial or residential space based on the application of a usage model of the space. In a home, for example, the kitchen area would get a different lighting experience than a living room or bedroom, yet all are implemented based on the CS recommendation as a guiding metric. And in each separate space, proper specification of a Ketra system would take into account the optimal layered light approach. At any given point in time, people need different light output from ambient, decorative, and task lighting.

Ketra considers its value proposition of delivering natural light to people in artificially-lit spaces more as perhaps a media company would as opposed to how traditional lighting companies have contemplated the challenge. Hamilton describes what a Ketra system outputs as "curated content." The control system delivers the content stream throughout the house programmatically over the course of a 24-hour day, with input from the people in the space to further change the settings based on preference.

FIG. 3. A control panel in a living space includes the typical scenes that might be set via the Ketra software along with a legacy dimmer that can work with an incandescent or halogen lamp.

The Ketra control system generally supports four scenes in any given space. The four scenes might have different names and vastly different operational profiles in different spaces. Generally, the top scene on a Ketra control panel is Natural and that scene is utilized most frequently. Fig. 1 shows a typical Ketra control panel in this case installed in a dining area of the home retrofit project we followed. In a common area such as a living room or kitchen, the other scenes might be Entertain, Relax, and Energize.

So at any given point in time, in a Ketra-controlled and -lit space, there are three vectors that are in play resulting in the lighting SPD, intensity, and spatial distribution (let’s call it the lighting environment) being produced by the system. First, an occupant of the space may have selected one of the four preset scenes for the space using either a wall-mounted panel or a smartphone app. Second, the chronological program for the selected scene would adjust the lighting environment based on the time of day and day of the year. Third, an occupant in the space may have overridden one or more setting elements that comprise the lighting environment.

Technology stack

Having covered the operational basics of the system installed in the home retrofit, let’s consider the underlying technology. Ketra supplies all the key technology elements that comprise the system. When Ketra emerged on the SSL scene, its business plan was to supply control technology in IC form that would enable lighting manufacturers to more easily develop and deliver tunable systems. We covered the company first back in 2012 after an off-the-show-floor meeting at LightFair International when the company said it could use LEDs to both produce light for a tunable system while also using the modulated LEDs as color sensors that would ensure accurate mixes of spectra.

Ketra continues to utilize that original intellectual property today, but evolved to a business model of delivering the entire system. Hamilton has said the company evaluated technology elements from others, but found that the company could only deliver its vision of natural light by controlling every element of the system. You might think of it as a vertically-integrated company, although back in the day that term implied manufacturing everything — for example, IBM made microprocessor and memory ICs, hard disk drives, displays, and the computer. Ketra doesn’t manufacture its own LEDs, but has partnerships that afford it a fully-customized light engine. The company is vertically integrated in terms of intellectual property.

The light engines in its lamps and luminaires still produce and sense light, according to Ketra. The sensing element allows precise control of SPD that doesn’t waver over time as the LEDs age. Ketra will not specify how many channels of LEDs and drivers it employs in its natural-lighting offerings. Many white-point-tunable products simply use warm- and cool-CCT LED channels. Ketra’s system can produce colors as well, so certainly more channels are in play. However, the goal wasn’t a color-changing system per se, but rather Ketra believes that more channels are needed to hit the white SPDs that are necessary to deliver on the CS work of the LRC and Ketra’s ideal of achieving natural light.

FIG. 4. The lights deliver rich red and high CRI across the full range of CCT options as seen in this SPD graph.

The company also utilizes a proprietary wireless network. It is actually based on the same IEEE 802.15.4 wireless mesh network that underlies ZigBee and Thread networks (based on IPv6 protocols). But Ketra added security and other functionality to its system. The company supplies its own network gateways and other elements. Ketra said it has installed systems with as many as 10,000 nodes and that it had to bolster the capability of the standard network stack.

The lighting portfolio includes a variety of replacement LED lamps in various form factors along with some luminaires. In Fig. 2, the inset shows the company’s A-lamp while the main photo depicts the S30 directional lamp installed in a recessed housing at the project home. In terms of luminaires, the company has downlights meant both for retrofit and new construction projects, linear fixtures in recessed and pendant form factors, linear wall washers, and track lights.

The Ketra platform can also support legacy lamps that use phase-controlled dimming. Such products can only be dimmed, as opposed to tuned, but the Ketra controls can automatically set dim levels or allow a legacy dimmer to override the system setting. Fig. 3 shows a Ketra panel that also includes a manual switch/dimmer that can work with an incandescent or halogen lamp.

Light quality

Having discussed the technology stack, let’s take a technical look at the light produced (in Part 2 of the story we will get to the visual look of the lighting in the space). Fig. 4 is an SPD graph of a Ketra lighting product that is programmed for maximum CRI mode. The graph depicts the light source performance over the range of 1500K to 6500K CCT.

The graphs are very interesting and truly demonstrate that CCT is not a very good way to characterize light output. You will regularly hear that cool-CCT lights have too much blue spectral energy and no red. But Ketra’s multi-channel system adds red energy even in the cool settings and delivers outstanding CRI. Moreover, all of the settings deliver a smaller blue peak and more uniform SPD than does the typical phosphor-converted white LED, with the exception of the 1500K setting where clearly it’s primarily the red channel of the system producing light.

Stay tuned for Part 2 in an upcoming issue. We will explore the project visually, learn about the installation and commissioning process, and discuss the experience of the homeowner.

Get more in-depth, in-person education on human-centric lighting science and applications at our upcoming Lighting for Health and Wellbeing Conferences. Visit for program information.

About the Author

Maury Wright | Editor in Chief

Maury Wright is an electronics engineer turned technology journalist, who has focused specifically on the LED & Lighting industry for the past decade. Wright first wrote for LEDs Magazine as a contractor in 2010, and took over as Editor-in-Chief in 2012. He has broad experience in technology areas ranging from microprocessors to digital media to wireless networks that he gained over 30 years in the trade press. Wright has experience running global editorial operations, such as during his tenure as worldwide editorial director of EDN Magazine, and has been instrumental in launching publication websites going back to the earliest days of the Internet. Wright has won numerous industry awards, including multiple ASBPE national awards for B2B journalism excellence, and has received finalist recognition for LEDs Magazine in the FOLIO Eddie Awards. He received a BS in electrical engineering from Auburn University.