The potential of lighting to improve occupant health and well-being is increasingly attracting the attention of project owners and end users. In commercial environments, good design has become synonymous with talent hiring and retention. The benefits of well-lit spaces map across other regularly occupied building typologies, such as residences and schools, as well as patient rooms in healthcare and assisted-living facilities.
“If you don’t get the lighting right, it’s not going to be an environment anyone wants to spend time in,” says Elizabeth O. Lowrey, principal and director of interior architecture at Elkus Manfredi Architects, in Boston. “It all goes back to making people feel good and look good.”
“Clients are increasingly requesting and expecting lighting systems and applications that can support human health and well-being and make an impact on the circadian system,” concurs Mariana Figueiro, director of the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute, in Troy, N.Y., where she is also a professor at its School of Architecture.
In response to demand, lighting manufacturers are launching new products that they allege to be attuned to our circadian rhythm. Yet the skeptical architect and end user have to wonder: How much of this is marketing versus actual science? Is circadian-attuned lighting any better than conventional products?
What You Can’t See
Both daylight, courtesy of Earth’s 24-hour light–dark cycle, and electric light can drive our circadian system, our internal clocks that regulate daily behaviors and the timing of biological processes, such as the release of the hormones melatonin and cortisol, which help control our blood sugar and affect our energy levels.
Several characteristics of lighting, including quantity, spectrum, timing, duration, and distribution, determine its nonvisual effects on our bodies and minds. The influence can be positive, but also negative if, for example, light is delivered at the wrong time. Think screen time on electronic devices before bed or in the middle of the night. The disruption of circadian rhythms has been associated with health problems such as metabolic diseases, depression, and some types of cancer.
“We don’t fully understand everything there is to know about light’s nonvisual effects, but we know enough from the research over the past 30 years to be able to apply light to improve sleep, mood, and well-being in a variety of environments,” Figueiro says.
The LRC, for one, develops metrics and tools to help lighting designers understand and apply circadian light in the built environment. Circadian stimulus (CS) measures the effectiveness of the retinal light stimulus for the human circadian system from threshold to saturation; in other words, this metric allows designers to compare the ability of different light sources to stimulate the circadian system. With funding from the U.S. General Services Administration, the LRC has conducted several studies that found office workers receiving high CS throughout the workday felt more energetic and alert than workers receiving low CS. The former group also experienced better sleep and felt less depressed.
Daylight, Mimicked
Generally speaking, natural is best and lighting is no exception: Daylight is the ideal source for regulating the circadian system. However, people tend to spend most of their day in interior environments, the majority of which Figueiro believes are under-lit: “Due to restrictive energy codes, daytime light levels in buildings are often too low or at threshold for activating the circadian system,” she says. “Even in open offices with many, large windows, workers do not receive enough daylight to stimulate their circadian system, due to factors such as season, cloud cover, desk orientation, and window shade position.”
Supplemental electric lighting is thus a necessity, and recent technologies have enabled and improved the ability of fixtures to work in tandem with daylight. For example, luminaires with integrated photosensors and automatic dimming can maintain consistent light levels regardless of fluctuations in available daylight. Advancements in LED technology have also fostered the creation of tunable white light systems, which mimic daylight patterns by adjusting correlated color temperature (CCT) and brightness levels throughout the day.
“Many manufacturers have made claims of tunable white light fixtures [that can change in CCT] as ‘circadian,’ ” says Keith Yancey, AIA, principal at architectural lighting consultancy Lam Partners, in Cambridge, Mass. “While there is clearly a perceptive difference in CCT, which can make spaces feel warmer or cooler, actually stimulating the nonvisual cortex requires increased light levels in order to be effective.”
Though tunable fixtures may be worthwhile, Yancey cautions that increased lighting levels and sources rich in the blue spectrum (CCT exceeding 5000K) can create eye fatigue and glare if not properly implemented. For lighting to achieve CS and still feel normal and comfortable to our eyes, he recommends focusing on the proper wavelength, and not simply providing high light levels or cooler color temperatures.
To change CS values, Figueiro advises, simply increase or decrease light output while fixing CCT. If energy codes are restrictive, she suggests choosing a source that emits more short-wavelength light and picking a luminaire distribution that provides a higher horizontal-to-vertical ratio for visual tasks, such as surgery or reading paper documents. But that doesn’t mean designers can neglect vertical illuminance, which is what stimulates the brain. “Designers need to think about lighting beyond the ceiling and bring the source close to the eyes,” she says. She advises that designers aim for a distribution of light with a horizontal to vertical illuminance ratio of at least 7:10.
Utilizing LED lighting panels as luminous vertical partitions is another economic way to change occupant energy levels. Saturated blue light can promote alertness in morning, and then transition after lunch to saturated red light, which still stimulates energy levels without raising CS to levels that may affect sleep later.
Painting with Light
More recent design approaches favor using layers of light from a variety of sources to mimic the effects of natural light, rather than simply delivering white light to surfaces via ceiling-mounted fixtures. Natural light is uneven—brighter areas are offset by shadows—and this contrast creates visual interest.
“We are thinking a lot about the changeability and diversity of light, particularly in open plan environments,” Lowrey says. “Consistent lighting can be rigorous and creates fatigue.” She advocates for “painting” surfaces with layers of light, such as task lighting for work surfaces, focused light to highlight artwork or significant architectural features, and a mixture of up- and downlighting throughout.
Currently, Lowrey is exploring the movement of light and shadows in common spaces to match the morning light outside. The lighting patterns will subtly evolve throughout the day, resulting in a dynamic space.
Though fixtures designed to influence the circadian system are more expensive than standard white lights, implementing circadian lighting strategies doesn’t have to be expensive. One economical approach Figueiro suggests is designating a space as a “light oasis,” a room within a commercial space that is bathed in color-tuned light and where occupants can visit in the morning for their daily circadian dose.
The Verdict
While research on the effectiveness of circadian-attuned light reveals several benefits, the bigger picture from a design standpoint is important. “Sleep regularity and quality are very well proven to be connected to mental and physical well-being, but it would be taking liberties to connect a healthy lighting diet directly to these results,” Yancey says. “Light, while the primary time-giver to the body’s master clock in the brain, is only one of many factors,” which also include eating schedule, external stressors, and social stimuli—such as “Instagram at 1 a.m.–sleeplessness.”
“It’s analogous to climate versus weather,” Yancey continues. “We may not be able to predict the weather, but we have a pretty good sense of the climate. Similarly, we don’t see immediate and direct benefit with well-designed lighting for circadian health, but we can measure trends of performance and attribute certain gains to the lighting, at least in the research setting. The variables at play in real-life settings make it notoriously difficult to tease out cause and effect.”
“Providing occupants with proper circadian lighting is similar to providing them with ergonomic chairs or flat-screen computer monitors,” Figueiro says. “Offices with daylight are more valuable and can be sold or rented for higher value. The same can be established for offices with good circadian lighting.”
This article appears in the June 2019 issue of ARCHITECT with the headline "The Merit or Myth of Circadian Lighting."
Editor's note: This article has been edited since first publication to correct Lam Partners principal Keith Yancey's recommendation on achieving CS while remaining a semblance of normalcy and comfort to the human eye.
