Post Date: 07/31/23
Essentially indefinable, [light] is the ultimate food for our planet’s life and allows us to perceive the world in nearly magical detail and diversity.
Sonke Johnsen, The Optics of Life: A Biologist’s Guide to Light in Nature, p. 1
Agreement does exist that more research is needed to allow us to fully understand the impact of light, and until agreement is achieved the use of techniques that exploit the non-visual effects of light should be used with caution.
Arup, “Circadian Lighting – Definition and Strategies”
It doesn’t take a study to understand that light affects us psychologically and physiologically. Anecdotally, each of us knows how we respond to different types of light; from a bright, crisp sunny September morning to a dismal, dank and dreary December evening – even our language is replete with metaphors that harness our physical and emotional response to light, like using a “sunny disposition” to describe somebody who is cheerful and energetic. The same is true of artificial lighting, from the warm glow of candlelight in Wordsworth’s “Prelude,” to the toxic green street-lighting of Kirchner’s antebellum Berlin.
It is thus no surprise that lighting can impact mood in the short term, and health in the long-term. The degree to which it does either is, of course, contingent on the sensitivity of the individual and the duration or regularity of their exposure to any given lighting environment. When one introduces the capacity for light adaptation, or the affects of age, lifestyle, culture, environment, genetics and other variables (like indoor air quality), it becomes clear that while the influence of lighting is indisputable, its net non-visual effect for any one environment on any individual is fairly difficult to quantify.
To an extent, this explains the hesitancy amongst some lighting designers to adopt the Circadian lighting paradigm. Conversely, many lighting designers might be justified in thinking that Circadian design simply represents good, human-centric lighting that provides optimal visual comfort and acuity, while also promoting physical and psychological support through the introduction of life-giving natural light. Equivocation around Circadian design is only exacerbated by the fact that different groups have promoted varying narratives regarding how it is accomplished based on both the available science and technology. The goal of this article is to approach Circadian design critically, to review some of its claims, and its complications, in an effort to encourage a dialog on light and health, and the means of using the former to promote the latter.
What is Circadian light response?
It is impossible to understand Circadian design without understanding the Circadian light response upon which it is formulated. WELL’s WELLology on light provides a fairly nice summation of the history and science behind Circadian non-visual response. Circadian light response is premised on a process of photoentrainment by means of which diurnal animals (like humans) are synchronized with their environments such that they are awake when it is light, and asleep when it is dark in an approximate 24-hour cycle (the same is true for nocturnal animals, although with the opposite sleep / waking cycle). The mechanism behind photoentrainment is complex, but appears to be affected by the action of ipRGC (inherently photosensitive Retinal Ganglion Cells) that respond to narrow wavelength (446 - 483 nm) light.
In the presence of 446 - 483 nm light, ipRGCs produce a photopigment called melanopsin, which suppresses the production of melatonin, signaling the brain that it is light (the appropriate environmental for wakefulness). In the absence of this short-wavelength light (and thus melanopsin production), the pineal gland produces melatonin, which signals the brain that it is dark (the appropriate environment for sleep). Exposure to short-wavelength light during the evening / night, or a lack of exposure to it during the day can result in an asynchronous response, by means of which the body’s Circadian cycle comes out of sync with the environment.
Disruption of the Circadian cycle interrupts sleep patterns, resulting in a variety of ailments ranging from mild to severe. As a consequence, it is important for people to maintain photoentrainment with their environments to ensure appropriate levels of sleep, and thus sustained health. However, today (depending on geographical region and lifestyle) many people can spend over 90% of their lives indoors under artificial lighting conditions that do not necessarily follow diurnal patterns in terms of light spectrometry. In some climates, this figure can be as high as 99% of time spent indoors.
The theory of Circadian design posits that in environments where there is insufficient daytime short-wavelength light, or an evening abundance of it, people are at risk of asynchronous Circadian rhythms, and thus have a higher probability for interrupted sleep and its negative health consequences. To offset this risk, Circadian design encourages the introduction of short wavelength light into indoor environments during the day (whether natural or artificial), and the reduction of it during evening and nighttime hours.
Disentangling Narratives of Health & Alertness, Circadian Lighting and Color Tuning
One of the issues confronting the adoption of Circadian design is that the current discourse contains several separate narratives that have become conflated, and not all of them support the health imperative. Similarly, even those that do support the health imperative may be overly simplistic in their approach. For example, in the WELL description of Circadian design mentioned above, the WELLology tends to conflate the purported health benefits of Circadian design with economic benefits that accrue to institutions and corporations who adopt Circadian principles in terms of the increased productivity and focus of individuals.
Improved cognitive function and focus are natural consequences of better sleep. Their affects benefit both the individual and the institution in environments where improved productivity results in positive yields. The inducement of improved sleep through Circadian design thus aligns with the stated goals of WELL, while the effects of improved sleep align with the interests of prospective clients (for example, schools). However, in instances where the alerting effect of high intensity, short wavelength light is sought solely for the sake of stimulating individuals during working hours, the prescription can have deleterious effects on visual acuity and health, resulting in fatigue, stress, anxiety and hypertension. In the latter, the principles of Circadian design are being employed, but in a way counter to the health imperative that supports the paradigm.
Likewise, the initial industry response to early Circadian research was the development of tunable white solutions that purportedly mimicked the ambient outdoor lighting environment. These technologies were promoted as supporting Circadian photoentrainment by increasing levels of short wavelength light during daylight hours, and reducing them during late afternoon and early evening hours. However, if a tunable white solution does not provide or eliminate the appropriate wavelengths of light at the correct time, then it would have little to no effect on photoentrainment, or could exacerbate asynchronous Circadian response.
In this instance, mimicking natural environments as an aesthetic goal became conflated with the Circadian interest in returning the body to natural waking/sleeping cycles. However, it is not purely the color of light that governs Circadian response, rather it is how that color is composed photometrically. A cool light that lacks the critical spectrum will be no more successful in stimulating the Circadian response than a warm light that includes it. Thus, when evaluating Circadian fixtures, changes in CCT are less important than the inclusion or exclusion of 446 – 483 nm light, and the time at which these wavelengths are introduced or removed.
In both instances, more research needs to be done regarding appropriate intensity and exposure levels of the critical wavelengths throughout the day, and a more pointed and clear articulation of both benefits and means provided. Variables like visual acuity and comfort, and the holistic health of the individual, should also be addressed, as well as the fundamental physiological and psychological differences between individuals, and thus their responses to light, which might involve a more individually defined system with nuanced local control. Finally, more research needs to be done regarding the cost / benefit of these types of solutions over time across a broader base of variables than those currently being tracked. Many WELL and LEED initiatives involve measuring and monitoring to determine ideal use-cases, and this should apply to Circadian design as well.
Technology is not the only solution, and not always the best solution
In a well-known installation, the artist Laurie Anderson plastered the walls of the Hirshhorn Museum with the quote, “If you think technology will solve your problems, you don’t understand technology – and you don’t understand your problems.” The ability of technology to fix problems that it often poses has rarely (in my experience) manifested results that do not themselves involve new problems. While there are many things about contemporary buildings that can and should be improved to advance the health and well-being of occupants, the solutions can embrace a broad range of high- and low-tech strategies, understanding that whatever solutions are proposed will invariably have limitations in application and efficacy.
For example, in much of the current literature on Circadian design, the assumption appears to be that the subject is inherently static. While it is true that for many who work in American offices (for example), the norm may be a sedentary experience governed by hours localized in a small space in approximately the same position, perhaps the issue with the paradigm isn’t the lighting (although it can contribute) but rather how offices are designed, and the expectations of the workplace. These are, of course, as much cultural issues as they are design ones, which makes them more difficult to study and address than simply adding a tunable white desk lamp or complex sensor network.
However, some companies have already adopted alternative cultural models, and alternative office and campus plans that incorporate a variety of spaces, or reconfigurable spaces that allow individuals or groups to choose between optional environments for work throughout the course of the day. These cultures and designs encourage movement, interaction and choice, and show strong benefits in terms of employee morale, retention, collaboration and creativity. Thus, while Circadian photoentrainment might be a contributing factor to health, it is only one amid a plethora of other variables impacting wellbeing, and there are a broad range of other tools available to mitigate some of the ills of our current cultural paradigm. Similarly, designs that encourage movement and focus on morale show that different values can be at play in the design of space, like encouraging creativity and supporting comfort (rather than enforcing alertness).
Even an “ideal” office design has its limitations, insofar as immersion in this kind of environment (in most instances) has definitive beginning and end points. Since one of the more significant contributing factors to sleep cycle issues seems to be exposure to short wavelength light at night, this means that Circadian strategies in homes or neighborhoods might be more important than their implementation in office environments, where either individuals are no longer working, or if they are, they need to be alert to complete tasks. High levels of blue-light trespass in the form of electrified signage, streetlights, exterior / landscape lighting or even headlights, blue-light from appliance indicators, alarm-clocks or other devices, and of course nighttime screentime can all have greater impact on Circadian photoentrainment than Circadian strategies adopted at the office.
One of the more compelling aspects of the Circadian lighting paradigm is the advocation for natural daylighting strategies, although in this regard (as in all others) one should be wary of employing the same strategy universally regardless of climate, culture and geographical location. Daylighting strategies appropriate for the Northeastern United States may not be appropriate for Abu Dhabi or even Arizona, much less cities like Reykjavik which experience seasonal periods of white night during which the sun doesn’t set. While one should always be wary of designing to the exception rather than the rule, the variability in climate, ambient lighting conditions, and cultural values suggests that “global” or solipsistic approaches to this type of design can be as harmful as they might be healing.
Conclusion – where do we go from here
There is an extensive and compelling body of research that shows that there is a non-visual response to short wavelength light that is critical to photoentrainment, and thus the maintenance of Circadian cycles of waking and sleep. Furthermore, the mechanisms behind Circadian photoentrainment are fairly well understood and documented. There is also a compelling body of research that documents the ill health consequences of poor sleep which can occur in instances where an individual’s Circadian rhythm is out of sync with their environment. Much of this research originates in the biological, neurological and medical fields, and little of it is prescriptive in terms of design standards.
Studies explicitly focused on lighting or architectural design in relation to Circadian photoentrainment have thus far been inconclusive. In some instances, prescriptions resulting from these studies ignore fundamentals of good lighting design, including the requirements of visual acuity and comfort, in others, the studies’ limited foci do not account for real-world variables that could impinge upon their results. The variables affecting individual sleep and health may be so numerous, various and complex that localizing cause to the effects of artificial lighting will require carefully constructed studies that account for such variation, while determining the extent to which design strategies focused on photoentrainment improve health may require large scale implementation and prolonged study.
Does this mean that manufacturers should entirely ignore Circadian design? No. Understanding non-visual response to light can, and perhaps should, inform product design decisions, but not at the expense of visual acuity and comfort, nor necessarily at that of other important quantifiable metrics, like energy consumption. More importantly, the purported health benefits of Circadian design should be separated from and carefully balanced against claims regarding alertness or other ancillary benefits used to prove RoI for expensive lighting infrastructures.
For lighting designers, any artificial lighting systems that purports to support the goals of Circadian photoentrainment should be thoroughly vetted. There are a number of really good manufacturers who have invested considerable resources into understanding Circadian photoentrainment, and developing technologies to help support it. These manufacturers have extensive documentation on their websites, and many partner with local researchers and institutions to create research of their own (although, in this regard, study parameters and structure should be evaluated, and it is best if the study has been through peer review).
In the end, Arup’s position of cautious adoption perhaps best acknowledges our current level of knowledge, especially where other variables may inform decisions around the adoption of Circadian design principles, including cost and environmental performance. Conversely, if there is an opportunity to improve the lives of building inhabitants through the intelligent design of building systems, then that opportunity should at least be explored, if not tested, especially in instances where the benefits may outweigh the harm. Finally, Circadian design should be disentangled from the discourse of tunable white solutions; the artificial introduction or removal of the action spectra is only one solution among many.