Feb. 22, 2022 - It's a stat that comes up a lot, especially when smart buildings are being discussed: Human beings in the 21st century spend roughly 90% of their lives indoors. It's not a surprising number, but it's inarguably unnatural — people evolved over centuries spending the bulk of their time outside, following the cycles of daylight. Light suppresses melatonin, the hormone that plays a role in triggering sleep. (It's a big factor in the advice you'll hear from folks in the medical field when they remind you to put down the smartphone well before bedtime.)

But indoor light has evolved over the decades, too, from a binary on/off selection to the development of the dimmer to today's tunable fixtures. Those fixtures — including those most recently introduced by Crestron — give the occupant of any building full control of the color of their lights, including hue, saturation, color temperature, and intensity.

The ultimate goal is creating spaces that are illuminated in a "biocentric" manner, a way that matches what's called the circadian rhythm: "Circadian rhythms are 24-hour cycles that are part of the body's internal clock, running in the background to carry out essential functions and processes," notes this definition by the nonprofit Sleep Foundation. Furthermore, "One of the most important and well-known circadian rhythms is the sleep-wake cycle." All of this means that there's a staggering number of variables to take into account when tunable lighting becomes part of a smart home design.

One of Crestron's Residential Products Managers, Victor Menendez, has been studying the topic for years. He's got advice on how to simplify one's initial approach: "In the world of tunable white light, the two terms to focus on first are temperature and color rendition."

"You illuminate everything and anything that you can with daylight and then you supplement light based on the needs for those areas." – Victor Menendez, Crestron

Kelvins and CRI — Temperature and Rendition

The U.S. Department of Energy has some useful definitions on the energy.gov website, including an excellent explainer on color temps:

By convention, yellow-red colors (like the flames of a fire) are considered warm, and blue-green colors (like light from an overcast sky) are considered cool. Color temperature is measured in Kelvin (K) temperature. Confusingly, higher Kelvin temperatures (3600–5500 K) are what we consider cool and lower color temperatures (2700–3000 K) are considered warm. Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing.

In fact, the bright white light you'd get from clear conditions at high noon is a "cool" K temperature, and that triggers the alertness and productivity that's optimum in the middle of a workday, while those warmer K temperatures match the sunrise/sunset colors that tell the body to either wake up or wind down.

Color rendition is measured by CRI, the "color rendering index," which tells the user how well an artificial light can mimic the sun on a 1-100 scale. "A CRI of 80% or better is decent, but today's best fixtures strive for a CRI above 90 — and that's important for a variety of reasons," Menendez explains. "If you're in the kitchen, you want to see the color of your meats, produce, or fruits. If you're hanging a painting, you want that artwork to be lit so that it's true to the creator's intent." Menendez has a favorite demo that he's brought to a number of Crestron NEXT events: a painting that changes dramatically as a variety of lighting factors are adjusted.

What's the Lamp Supposed to Do?

Understanding how people interact with light is truly key to creating effective architectural lighting solutions. Is it ambient light, providing general luminescence? Is the fixture used to illuminate a task — is it lighting the space where you cook, for example? Or is it accent lighting that draws attention to a special vase or traces the lines of a dramatic feature of the building, like a staircase?

Determining what the light's function is informs placement of a fixture — locating a kitchen light so that the countertops aren't cast in shadows by objects like cabinets or people working in the space, for example. For ambient light, likely the bulk of most installations, automating the functions of tunable fixtures can create what's called "biomimicry" — in this case, imitating the cycles of daylight.

"We've developed a really elegant solution for mimicking changes in natural color temperature," adds Menendez. "It's been dubbed the Crestron SolarSync sensor, and it matches the light outside." Simply put, it's an outdoor sensor that communicates the outside color temperature to the Crestron Home™ platform in real time.

Getting Daylight in the Mix

Of course, these advancements all work best when there's some kind of actual daylight in a building. Ludwig Mies van der Rohe — one of the best-known Bauhaus architects — once said, "The history of architecture is the history of man's struggle for light — the history of the window." It's what informs the Bauhaus-inspired glass-and-steel office and apartment buildings that can be found from New York City to Chicago's Lake Shore Drive to the urban centers of the West Coast.

When Menendez speaks to residential tech professionals about their options, he says, "I very much talk about the importance of the connectivity to the outside. I sit next to a window all day, and I'm very connected to it. I feel the sunlight — it's incredibly important." When Menendez is talking about holistic building solutions, he begins with allowing as much daylight into the structure as is possible — and that's an area where shading solutions come into play.

"When you're doing a design, you first start with daylighting. You illuminate everything and anything that you can with daylight and then you supplement light based on the needs for those areas." Does the space demand ambient, task, or accent light beyond the daylight coming in?

Another factor that affects the design is a simple one: paint. Menendez quotes a paper titled Circadian Effects of Daylighting in a Residential Environment: "While it is not new knowledge that white paint leads to a brighter space, it is notable that white paint alone can result in an increase in daylight …," so much so that it's akin to adding no less than 55 circadian "days" to a building's daylight cycles.