Circadian Lighting Solutions Are Real and Important—Why Aren’t They Being Used?

An ongoing survey of designers reveals the challenges they face and how they can be overcome.
Circadian Lighting Survey

The Honeybrains cafe, located in Manhattan’s Noho neighborhood, features circadian lighting design by Lumen Architecture. Courtesy Magda Biernat/OTTO

Edward Clark, director of design firm CIRCA DIESfocuses on the interface of building occupants and high-performance building strategies. His expertise in the circadian lighting field was honed at ZGF Architects, where he was instrumental in the research and application of circadian lighting strategies for healthcare and workplace environments.

Natalia Lesniaklighting designer at Lumen Architecture, has worked on experiments and research that focus on the impact of light on circadian rhythms, cognitive performance, and on the development of research-based light therapy and design strategies. She works on a range of residential, office, hospitality, retail, and other commercial projects where she advises on the integration of circadian research.


Light is the primary stimulus that synchronizes our body clock with the solar day. Our bodies evolved at a time scale much slower than the rate at which we alter our environment. American spend 95 percent of our time in indoor environments that are novel in comparison to our evolutionary past. At night we are bombarded by light from personal devices, televisions, street lamps, signage, and more. Consequently, we receive too little light during daytime hours and too much light at night. This is exacerbated in northern latitudes where the days are shorter and daylight less intense. Add cloudy or overcast climates, and the daylight resource found in buildings is woefully inadequate at supporting our body clocks.

Electric lighting solutions typically focus on lighting tasks and provide light levels that are not intense enough to stimulate the circadian system. Insufficient light resources and an errant body clock can result in poor sleep, higher stress, lower productivity, Seasonal Affective Disorder, and has been shown to contribute to chronic health maladies such as Type 2 diabetes, cardiovascular disease, and increased occurrence of breast cancer. Circadian impactful lighting solutions seek to provide light resources more aligned with the environment in which we evolved, helping to regulate our body clock and reinforce our relationship with the sun and its daily and seasonal patterns.

The recent award of the Nobel prize in medicine to three Americans “for their discoveries of molecular mechanisms controlling the circadian rhythm” has brightened the spotlight on the connection between light and wellness. Supported by a flurry of media responses and a plethora of supporting evidence, the design industry should feel emboldened to integrate circadian lighting solutions into every project. Although the awarded studies were conducted in the mid-80s, and numerous research results have supported and greatly expanded our understanding of the relationship between light and health, so far the practical application of circadian lighting solutions has been minimal. Despite a market full of such solutions, adoption has been relatively slow. Why is this? What is the current state of practice? Where are the doubts, are they well-founded, and can we move past them?

A recent survey of practitioners, lighting reps, academics, and researchers, helps to answer these questions as well as highlight knowledge gaps and opportunities for improved execution.

The survey was completed by 101 respondents from across the U.S. who have varied levels of experience and a diversity of roles in practice. While this is a small subset, the survey results illustrated a rather sophisticated baseline level of knowledge and highlighted challenges of applying circadian solutions.


What are the largest obstacles you encounter in the design and application of circadian lighting? (Choose as many as apply,)

Circadian Lighting Survey

Outside of cost concerns, client and practitioner skepticism outweigh perceived technical difficulties in employing circadian informed design strategies. Lack of access to research, knowledgeable consultants, and case studies, or doubt in manufacturer claims can be reflective of a very busy practice that has limited bandwidth for deep dives into new solutions and complex ideas.

That said, the greatest hurdle indicated by survey respondents was cost. Color-tunable fixtures do come at a cost premium of an additional 20 percent to 200 percent when compared to a static white LED fixture and may be priced even higher due to “fear-based pricing.” Elevated pricing due lack of familiarity with new concepts and technology is a mechanism for design professionals and contractors to mitigate the risk of the unknown. Connecting professionals with others who have completed similar installations, providing pricing from those installations, as well as being honest with potential challenges can alleviate worry and result in pricing better aligned with the market and the project goals.


When designing a circadian impactful project, which practitioners did you work closest with? (Choose the top three.)

Circadian Lighting Survey

There is a productive opportunity for architects and lighting designer to collaborate more closely with interior designers, commissioning agents, and researchers or medical professionals. Practitioners can significantly benefit from early and deeper discussions with these overlooked collaborators. The whole of the world is a filter for light, with every reflection, passage, or refraction in an interior altering the spectral content of the light source, thereby dramatically altering light’s spectral content emitted from the source and impinging upon the occupant’s eye. This yields potentially unexpected and undesired appearances, and can dramatically alter the light resource and its impact on the circadian system, further reinforcing the need for increased collaboration between lighting professionals and the interior design team.


Which circadian metric do you use in practice?

Circadian Lighting Survey

Nearly a third of the respondents expressed confusion over which circadian lighting metric to use for assessing a circadian resource. This is a very hot topic in the industry and red hot in the academic world, at least the world that revolves around circadian light. There are two distinct camps: circadian stimulus (CS) developed at the Lighting Research Center at Rensselaer Polytechnic and melanopic lux (ML) developed at Manchester University, which has been adapted as equivalent melanopic lux (EML) and incorporated into the WELL Standard. While there is plenty of contention in academia over the details of the metrics, both party’s end goals are the same: to bring awareness to the impact that light has on human physiology and to provide a framework for understanding how the characteristics of light (spectrum, intensity, and duration) impact human physiology. The authors of both metrics have created spreadsheets, both free for download (see links above), that quantify CS or ML from a few standard inputs: the spectral lighting distribution (SPD) and the illumination level at the occupant’s eye in lux. One can design a circadian impactful lighting solution with either metric, yielding results that rival a conventional lighting design.


What strategies were included in those projects? (Choose as many as apply.)

Circadian Lighting Survey

Using a tunable LED fixture, one that changes spectral composition (color) from warm to cool, or specifying a static correlated color temperature (CCT) of a LED fixture (2700 being warm, and 6500 being cool) are the most common circadian electric light solutions employed by survey respondents. A static fixture can be used to impact the circadian system but is accompanied by a few challenges. Keep in mind that the higher the CCT, the greater potential impact on the circadian system. Without tunable fixtures, you lose the ability to modulate the circadian resource without dramatically altering the illumination level. Some solutions might not warrant variability of color temperature due to occupant demands or occupant schedules. Schools, for instance, might not be occupied in the evening and could use a static cool CCT along with slight variances in illumination to achieve the desired stimulus in the morning hours and a reduced stimulus prior to leaving for the day. Although CCT has been referenced for the ease of understanding, the spectral power distribution of the light source should always be scrutinized to understand the potential impact on the circadian system.


Do you test/simulate the circadian light installation during the design process?

Circadian Lighting Survey

Most respondents never or rarely simulate the circadian resource during the design phase. This may be a result of a very limited or complete lack of simulation scope or perhaps the design team lacks the skill set required for complex simulation. It is advisable to simulate both the electric and daylight sources iteratively as the design advances to yield an integrated and thoughtful design response to ensure that the design intent is met. There are several methods to simulate the circadian impact of lighting during the design process that could be readily integrated into the standard analysis workflow. Often analysis is completed for daylight distribution, glare, or visual comfort, or to inform the lighting design. Simulating the circadian resource is a logical extension. Be aware that not all analysis pathways yield the same level of fidelity. Some pathways treat light and materials as neutral (whites or shades of grey) and therefore fail to capture the interaction of light spectra and material spectral qualities. This deficiency can be partially rectified through either the CS or ML/EML excel calculators which will account for the color of light, but this process can be insufficient if a broad color pallet is used within the designed space. For example, understanding the interaction of light and color becomes pertinent with the use of indirect fixtures within a space clad with wood or other warm-toned materials.


How important is it to commission the lighting system?

Circadian Lighting Survey

Is a photospectrometer or similar device used during commissioning?

Circadian Lighting Survey

While nearly everyone agreed that commissioning is important, very few people use a photospectrometer or similar tool to verify if the installed system meets the design intent. The design intent is not solely the illumination level at a task surface, but specified in circadian stimulus or melanopic lux at the occupants’ eye during specific intervals throughout the 24-hour cycle. A photospectrometer measures the intensity (lux or foot-candles) and spectral content of light (SPD). CS or ML/EML cannot be calculated without this information and thereby the design goals cannot be validated. If proper testing is not completed in the field, you cannot verify that the proper stimulus has been provided, and risk providing a benign solution that came at additional cost to the client or–even worse–a negatively impactful solution.


Circadian Lighting Survey

We are at the beginning of a lighting evolution driven by the convergence of technical opportunity and the revived awareness of the impact of buildings upon occupant health and wellness. Providing light solely for visual needs and tasks does not leverage the full capability of the lighting systems of today and tomorrow. The science is understood and the technology is available, but we as an industry adopt change slowly, for several understandable reasons. The status quo allows us to minimize risk through “known quantities and processes” and provide our projects on time and on budget, but are we missing something essential along the way. Focusing on maximizing the benefit for occupants and shifting cost/benefit analysis to be occupant centric will push the design process and the solutions away from the status quo and towards truly nurturing environments.

Please follow this link to participate in the survey.

You may also enjoy “Blue Light is ‘Catnip’ For Our Physiology, But Designers Need to Control It Says ZGF’s Daylighting Specialist.”

Categories: Design, Interiors, Lighting

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