What is Circadian Lighting?
Over the years, circadian lighting and its applications have been explored by healthcare, senior living, commercial office and residential spaces, so even if you’re not deep into wellness design, there’s a chance you’ve heard about it. In asking what circadian lighting is, it’s important to note what the name is referencing.
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.
What’s Wrong with Traditional Lighting in Buildings?
The issue with the way most indoor spaces are lit comes in when considering how most modern lighting works. An average incandescent or fluorescent bulb often operates on a fixed color temperature, and in many cases a fixed brightness as well.
The problem is that in the grand scheme of evolution, human exposure to incandescent lighting has been short, not nearly long enough to allow for adaptation to this new stimulus. For all that its worth, modern lighting was made to keep humans operating well into the night for the sake of productivity, and it does its job well. However, because of this, the body often has no reference point of when to slow down or stop, which can in turn lead to disruptions in the circadian rhythm which then leads to disruptions in sleep.
Research helps back up this claim, with a litany of studies exploring the ways in which modern lighting impacts the circadian rhythm. Timing, intensity, color temperature and even the spectrum of light fixtures can potentially affect the circadian rhythm for the worse.
For instance, blue light, which is more commonly put off by computer and phone screens has been found to suppress melatonin (the hormone that helps regulate sleep) in humans. Another study, this time looking at intensity, found that, when exposed to a bright stimulus in the evening, the body will halt melatonin production for up to an hour.
A poor sleep schedule, or lack of sleep in general, then transfers into other issues such as fatigue, obesity, diabetes, depression, mood disorders and sleep disorders. It can make it exceedingly difficult to focus throughout the day and thus make general navigation of one’s environment markedly more difficult.
How Circadian Lighting Works
Circadian lighting works through entrainment, or, stimulating the body at the right time consistently to correct its circadian rhythm. In order to adequately influence the body’s circadian rhythm, circadian lighting manipulates a combination of both visual and non-visual stimuli, which can be listed off as:
- Color temperature (CT)
Color temperature relates to how white light is perceived by the eyes. Red and yellow tones are perceived as being warm while blue and pure white are perceived as cooler. These variations are 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. To paint a better picture, the average CT throughout the day ranges from 2700K (dusk and dawn) to 6500K (high noon), with bodies being the least active during the lower ranges and most active during the higher ranges.
With circadian lighting, the CT of light fluctuates in much the same way. Likewise, intensity starts low and rises up before dropping back down in the evening, delivering the same messages to the eyes that they would receive from the sun. However, these elements won’t be as effective if something like the spectrum, timing or positioning is off.
Each light fixture has the capacity to behave vastly different from each other due in part to their varying spectral output, however, this can be measured through a light’s color rendering index (CRI). Measured 1-100, CRI relays how close a light comes to mimicking the sun’s spectral output, with lighting at or above 95, coming very close to natural daylight, which naturally has a CRI of 100.
Lighting fixtures are then positioned in ways that best represent the location where they would normally be seen. Warmer lighting is positioned closer to the horizon, and cooler lighting is positioned about, with the timing of each accurately representing the movement of the sun on a regular 24-hour cycle.
Through manipulation of these elements, designers, integrators and architects develop environments that help actively readjust the circadian rhythm of occupants to healthier schedules, which in turn, leads to improvements of many of the aforementioned issues.
How Modern-Day Technology Helps Even Further
Combining these principles with newer building technologies, professionals can and have crafted some incredibly unique and powerful solutions. Automated lighting control allows the implementation of schedules and scenes and make adjustments to the environment without a second thought. Many prominent manufacturers even have a default ‘circadian schedule’ pre-programmed into their systems to run out of the box.
Light sensors have also been gaining prominence, with their use being twofold. One records the current intensity and color temperature of the sun so that the control system can then replicate it, while the other helps pair artificial with natural lighting. Depending upon the saturation of natural light, the system can then increase or pare back artificial light. This last part is key as circadian lighting shouldn’t aim to replace natural light in buildings, only supplement and work with it.
With that in mind, the role motorized window treatments play comes into focus as well. During the day, shades can lower to help minimize solar glare while in the evening, they can keep out bright, intrusive exterior lighting. Not only does it play a strong role in triggering circadian responses, but it also provides tremendous visual comfort.
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.
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.