What is Circadian Lighting?

Circadian lighting, also referred to as human-centric lighting (HCL), is lighting that mimics the natural progression of sunlight throughout the day. ‘Circadian,’ refers to the circadian rhythm, the biological clock that runs on a 24-hour day/night cycle for rest and activity. When we talk about circadian lighting, it’s referring to light designed to retrain circadian rhythms for a better night’s sleep.

This is based on how the body reacts to the progression of sunlight throughout the day. The eyes respond to specific lighting conditions at specific times and in turn relay information to the brain to perform specific functions needed at that time. For instance, sunlight moving from bright to dim tells the body it’s time to begin winding down for the evening. Think ‘brighter days and darker nights.’ Circadian lighting aims to create a strong daytime signal during the day while greatly reducing it at night.

Because circadian lighting aims to simulate daylight most of its benefits can be traced back to the general benefits of being exposed to natural lighting. As a result, over the years, circadian lighting and its applications have been explored by healthcare, senior living, commercial office and residential spaces to either pick up the slack in locations where lighting is limited or fix many of the negative effects associated with how buildings are currently being lit.

But What’s Wrong with Traditional Lighting in Buildings?

The body still uses the cycles of the sun in order to regulate many of its processes. Without it, these functions gradually grow more and more out of whack. (Image by Rudzan/Adobe Stock)

The issue with the way most buildings are lit relates to how traditional lighting was first conceived. Artificial lighting was always meant to keep humans operating well into the night for the sake of productivity, and for all that its worth, it does its job well. Often operating on a fixed color temperature (CCT) and brightness, an average fluorescent bulb is designed to keep people active well past the sun’s departure.

The problem is that in the grand scheme of evolution, human exposure to artificial lighting has been short, not nearly long enough to allow for adaptation to this new stimulus, so our bodies still rely on cues from the sun in order to figure out when certain bodily functions should occur. Because of this, and because of many people’s constant exposure to artificial lighting, the body receives no reference point of when to stop or slow down like it does with natural lighting. This then leads to disruptions in the body’s circadian rhythm, which in turn leads to a disruption in one’s sleep schedule.

For instance, blue spectrum light, which is commonly produced by computer and phone screens has been found to suppress melatonin (the hormone that helps regulate sleep). Meanwhile, another study, this time looking at how the brightness of lighting affects us, found that, when exposed to a bright stimulus in the evening, the body will halt melatonin production for up to an hour.

And once the circadian rhythm is off kilter, it can lead to issues such as fatigue, obesity, diabetes, depression, mood disorders and sleep disorders. Certain immune functions, once regulated by the circadian clock, can even be disrupted. Overall, it can make it exceedingly difficult to focus throughout the day and thus make general navigation of one’s environment markedly more difficult.

Wait, What’s Color Temperature?

Much like the light of the sun, circadian lighting operates on a spectrum of color temperatures that change throughout the day. (Image by Macro Vector/Adobe Stock)

Correlated color temperature (CCT) relates to how ‘warm’ or ‘cold’ white light is when perceived by the eyes. Red and yellow tones are perceived as ‘warm’ while blue and white are perceived as ‘cold.’ These variations are then conveyed inversely in degrees Kelvin, with warmer temperatures being lower and cooler temperatures being higher.

Cooler color tones are associated with daytime lighting conditions while warmer tones are associated with the early morning and late evening times. As such, the body usually becomes more active with cooler CCTs and more relaxed with warmer CCTs (which might be why candlelight or the light of a campfire can be such a comforting sight). Generally, the average CCT throughout the day ranges from 3500K (dawn) to 5500K (high noon) before cycling back down to ~3000 (dusk). A fluorescent bulb, meanwhile–like the ones commonly used in office buildings–usually sits at 6500K.

So How Does Circadian Lighting Work Then?

Sunlight does more than change its color temperature and brightness throughout the day. Its positioning changes over time as well. (Photo courtesy of USAI Lighting)

Circadian lighting works through entrainment, or stimulating the body at the right time consistently over a long enough period of time to generate a specific response. Put more simply, it trains the body to act like its being exposed to sunlight. And there’s a variety of ways in which this is accomplished, often targeting both visual and non-visual stimuli. Changing the brightness and color temperature are two common methods, however, other factors that circadian lighting targets include:

• Saturation (how much light is filling a space)
• Positioning (where the light is coming from)
• Timing (when the transitions in lighting occur)
• And spectrum (like color temperature but more focused on non-visual wavelengths)

Through manipulation of these elements, circadian lighting systems better mirror the characteristics of natural sunlight, which in turn helps trigger a stronger circadian response. It might not be an immediate fix, but over time, with lighting in the home set to change on a specific schedule, the body will align itself to a more natural sleep/wake cycle guided by the lighting system. It’s in this way that circadian lighting helps correct many of the underlying health issues associated with fixed lighting.

Where Can I Learn More About Circadian Lighting?

This particular category of lighting is one of excitement and innovation. Research is constantly being conducted into its applications, and manufacturers are using that research to better inform their products, which already constitute a broad range of fixtures and systems to accommodate a broad range of budgets and environments.

Meanwhile, organizations focused on the development of healthier building environments, like the International WELL Building Institute and the Centers for Active Design, continually refine and tune their own guidelines to help architects, interior designers, lighting designers and CI professionals better tune their systems via an established framework. We also have plenty of examples of circadian lighting systems at work here on DesignWell, so professionals have a better understanding of how these types of installations can be set up and appear within a space.

Ultimately, circadian lighting provides a multifaceted solution that can be adapted to fit a variety of budgets and outcomes. At its simplest, it’s a tool to assist occupants in achieving a better night’s sleep. At its most complex, it is a proactive system geared towards occupant wellbeing guided by elements of design and technology working in unison, creating a beautiful, healthy and functional space.