The Rhythm Behind Design

By Craig DiLouie | Apr 15, 2020
Shutterstock / magic pictures / Lightspring / panimoni / istock / Yuriy Mazur




Lighting Roundtable: circadian-supportive lighting

Lighting systems are designed for vision and visual comfort, but science tells us light can also modulate circadian rhythms. The growing understanding of the relationship between light and health has fueled a new lighting trend in circadian-supportive lighting.

The lighting industry offers numerous products and has supported research and metrics development. Underwriters Laboratories recently published design guidance, and the WELL Building Standard recognizes the importance of circadian-supportive lighting, which is now actionable.

Some lighting professionals are embracing circadian-supportive lighting while others are taking a wait-and-see approach. Many manufacturers seem to be fully on board. While there may be debate about implementation, there is widespread agreement that sufficient light falling on the eye for an adequate amount of time during the day is supportive of circadian health. The question now is should practitioners wait for more research, or should they begin implementing circadian-supportive lighting strategies based on what is known today?

Mariana Figueiro

Mariana Figueiro, director of the lighting research center at Rensselaer Polytechnic Institute, Lighting Research Center: Our research over the past 20 years—both lab and field studies in populations such as office workers, U.S. Navy submariners, older adults living with Alzheimer’s disease and children in schools—has shown that lighting designed to maximally impact the circadian system will significantly improve sleep quality, depressive symptoms, daytime alertness and more. It is important to use, deliver and measure the right lighting to experience the positive effects. Although responses to circadian-­effective light do vary from person to person, a lighting system that delivers a circadian stimulus (CS) greater than 0.3 during the day—particularly in the morning—and less than 0.1 in the evening is a great starting point.

UL recently published the “Design Guideline for Promoting Circadian Entrainment with Light for Day-Active People,” DG 24480. The overarching goal of DG 24480 is to encourage practitioners to provide daytime levels of illumination in buildings that help people return to the more natural pattern of bright days and dim nights under which we evolved—i.e., sunlight during the day and firelight at night. Developed for public benefit, DG 24480 provides the foundation for lighting innovations and practices that serve the public better than is common today. We are hopeful that lighting designers, specifiers and other practitioners will begin to apply current research to help people live better right now.

Many manufacturers have taken the position that circadian-supportive lighting is now actionable and have a variety of products that enable changing light intensity and color spectrum. On the product side, there are potentially three elements: the light source itself and how it tunes, the control that enables or automates the tuning and possibly information, either generated by the system for analysis or fed to the system for a more tailored response. What does the ideal circadian-supportive lighting system look like, and what is its full capabilities?

David Ciccarelli

David Ciccarelli, vice president—dynamic lighting at Acuity Brands Lighting: Ten years ago, the focus for circadian-­supportive lighting was squarely on tuning color temperature to mimic what we perceive as a standard daily and seasonal cycle. With those color-tuning systems, there were limitations on how to engineer spectra. LED systems struggled to go beyond the classic die-phosphor profile, and adding additional discrete colors fell short due to complexity.

The focus on just color-tuning technology was shortsighted, but it provided a much-needed benefit: the expansion of control systems to include color as a main attribute and breaking away from simple on/off and clumsy dimming behaviors.

Meanwhile, university-level spectrum and timing research has matured and begun reaching into our industry. The WELL Building Institute, for example, has included circadian-supportive lighting to its recommendations, adding a spectrum component weighting to our familiar lux calculations. While the institute and other like-kind models don’t completely overlap, they do support the idea that lighting is a main contributor to our circadian systems and our built environment can play a larger role.

Further, the industry has advanced on spectral engineering using multicomponent phosphors and sometimes blended with nontraditional pump wavelengths. These engineered devices offer simplification of the system to produce tailored spectra, with the goal to be combined with regular drive circuits without complexity of multichannel systems.

Combining the advanced control systems developed for tunable white with the new spectrum gets us almost all the way there—the last bit needed is the sequence of operations based on clinical research. This is underway now by several universities and some startups with the ambition to change lighting again.

Color-tunable lighting can play a role in circadian-supportive lighting strategies, with spectral composition working in concert with the amount of light falling on the eye’s photoreceptors. How effective are these products? And is it enough to simply adjust to a cooler correlated color temperature in the morning and taper to warm toward the evening, or are more sophisticated products needed to enact recipes of specific wavelengths? Is there a good, better, best approach?

Bonnie Littman

Bonnie Littman, president and CEO at USAI Lighting: Each project is unique and may have completely different design goals in terms of circadian support. The effectiveness of circadian lighting is dependent on several factors, some of which are based on the fixtures themselves, some on the design of the space, and others by the individual themselves. Intensity, spectrum, time of day of the exposure, length of exposure and the light exposure throughout the day all play a part in whether the light impacts someone’s circadian cycle.

Today, a variety of standards and guidelines are available to help specifiers determine what is best for their project, from the circadian stimulus metric out of the Lighting Research Center, the WELL Standard, UL’s new Circadian Design Guide and more.

LED lighting with capabilities for changing light intensity and
 color spectrum is key to circadian-supportive lighting and many other lighting strategies. What are ideal applications for circadian-supportive lighting, and can the lighting use its capabilities for other concurrent task needs? What are examples of how this might occur, and what type of solution would be needed?

David Venhaus

David Venhaus, manager, training and curriculum development at the Lighting Solutions Center, Hubbell Lighting: At Hubbell Lighting, we’re seeing the most interest for tunable-white lighting in both healthcare and education. In the healthcare arena, there are multiple studies showing promising results in elderly patients suffering from dementia and Alzheimer’s disease. Tunable-white lighting systems have shown to improve sleep, treat depression and have a positive impact on overall mood. Additionally, in education applications, studies indicate students perform better, participate more, and all occupants of the space enjoy a more pleasant learning environment. This is especially apparent in special education applications where early adoption of these systems is showing very promising results.

With tunable-white luminaires available in multiple form factors like downlights, troffers and linear suspended forms, lighting designers have more design freedom than ever.

The advent of controls into lighting systems means that tunable-­white systems can be integrated seamlessly into either of these applications as part of the general lighting package. Preset scenes plus the ability to manually override and set lighting in the space allows lighting designers to meet design specific criteria like the WELL Building Standard, the new UL Design Guide 24480 or other prescriptive settings that healthcare and education professionals deem best for those occupying the space. We’ve also noticed that the best user experience requires proper training throughout the sales channel, from the manufacturer, to the lighting designer, contractor and ultimately the users of the space. Note that since electrical contractors are crucial link in this chain, proper training on the installation and commissioning of these systems is crucial to a good end-user experience.

The DesignLights Consortium (DLC) now recognizes color-tunable LED lighting in its Qualified Products List, which is used by many utilities to qualify LED lighting products for their rebate programs. How do the technical requirements for color-tunable LED lighting differ from static-color general LED lighting? What is the acceptance of color-tunable LED lighting among utility rebate programs, and how will this impact adoption of color-tunable lighting save energy while potentially being used in circadian-supportive lighting strategies?

Kasey Holland

Kasey Holland, technical manager at DesignLights Consortium: Color-tunable LED lighting products, as stated in the DLC Technical Requirements, are defined as products whose correlated color temperature (CCT) can be adjusted by an input control and provide white light at all input configurations. This differs from products that can deliver colored light—or full-color-tunable products­—a category of lighting the DLC does not qualify.

Unlike the typical DLC Technical Requirements that list multiple luminaires with a static CCT variation, this policy allows single luminaires capable of delivering consistent light output across a wide range of CCTs to be listed. For utilities, this single, color-­tunable luminaire can be incented for a broad range of applications or spaces that can be tuned in the field. This not only enables occupants to have more control over their lighting but can also be used in building-level applications, such as those desiring circadian-­supportive lighting designs, for example.

Generally, color-tunable products are acceptable in utility rebate programs but are not incrementally incented above non-color-­tunable products. As the industry standardizes on non-energy-specific lighting metrics, it is very likely that utility programs will incent highly efficacious, tunable lighting products such as those used in applications that require task-specific levels of light and must avoid impacting circadian rhythms. It is important to remember that timing, duration, amount and spectrum all play an important part in circadian-sensitive lighting designs.

UL recently published a guide enabling lighting practitioners to implement circadian-supportive lighting strategies in buildings, signaling UL believes circadian lighting is now actionable. In a nutshell, what are the benefits of electrical contractors getting on board with this trend, what is the process, and what new skills do they need to ensure the right systems are installed?

Adam Lilien

Adam Lilien, global business development manager, lighting at UL: The newly published UL 24480 design guideline helps specifiers implement lighting schemes to promote circadian entrainment for day-active and night-inactive people occupying indoor commercial, educational and industrial spaces. In short, this means more lighting during the day and less at night. The guideline addresses both design for static lighting, without controls, as well as color-tuning, dynamically-controlled lighting schemes.

Under these guidelines, existing and new spaces will be designed not only to meet current expectations—designing illumination for horizontal surfaces—but also for vertical illumination that enters the human eye. By delivering better sleep and the benefits that come with it, the building owner will want lighting that is highly sought after by businesses that want healthier spaces for their employees and building occupants.

As an electrical contractor, knowing how to work within these new design guidelines will make your firm more relevant to the lighting specifier as well as the building owner. As the industry adopts lighting for health and wellbeing, marketing your firm’s knowledge regarding human-centric lighting is important to growing your business.

I recommend selecting one person in your firm to study UL 24480, especially someone eager to learn a new set of skills. Focusing on the two-page, quick guide is a great start. Then, working with lighting specifiers you already know, partner to identify a customer, build a project and publish a case study on your website. Your inside expert should attend association meetings where circadian topics are discussed, and they should share their experience. Once people know that you are capable of delivering circadian lighting projects, 

About The Author

DiLouie, L.C. is a journalist and educator specializing in the lighting industry. Learn more at and

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