In December 2019, UL published Design Guide 24480, which provides guidance on how to design lighting systems that support circadian entrainment. To learn more, I talked to Adam Lilien, Global Business Development Manager, Lighting, UL, LLC. The resulting interview informed an article I wrote for the May issue of ELECTRICAL CONTRACTOR.

DiLouie: Please describe the new UL Design Guideline 24480: What is it? Who was involved in its development? What was the process of development? When was it published?

Lilien: The title of the document is: Underwriters Laboratories Inc. 24480 Design Guideline for Promoting Circadian Entrainment with Light for Day-Active People. I’ll refer to it in this interview as DG 24480. It was published in December of 2019. Underwriters Laboratories, Inc. is the not-for-profit entity. UL, LLC. Is the for-profit entity. As an employee of UL, LLC, with industry experience as a lighting manufacturer, lighting designer, and manager of electrical contractors, I served on the Task Force.

DG 24480 is a science-based design guideline, intended for use by those who design and specify lighting in buildings and wish to provide light for vision and for non-visual circadian entrainment for typical day-active and night-inactive people. As we have specified indoor lighting for vision for over 100 years, designing for health and wellbeing is a new practice that will take some getting used to. This document is a start. It intersects with Well Building Institute lighting guidelines, and as organizations such as IES and CIE prepare to publish their viewpoint on circadian lighting, this document will become one of the important tools for the industry.

In the end, DG 24480 is important as it introduces design guidelines based on the Circadian Stimulus (CS) method for lighting specifiers, manufacturers, electrical contractors and building owners to understand.

Underwriters Laboratories formed a task force, Chaired by Mark Rea, Ph.D, of the Lighting Research Center. Mark is a Professor of Architecture and Cognitive Sciences at the Lighting Research Center (LRC), and served as LRC Director from 1988 to 2017. Dr. Rea is well known for his research in circadian photobiology, mesopic vision, psychological responses to light, lighting engineering, and visual performance. He is the author of more than 250 scientific and technical articles related to vision, lighting engineering, and human factors and was the editor-in-chief of the 8th and 9th editions of the Illuminating Engineering Society (IES) Lighting Handbook. He has been elected Fellow of the Society of Light and Lighting (UK) and Fellow of the IES. In addition, he is recipient of the IES Medal.

The makeup of the Industry Task Force developing the Design Guidelines relied on a cross section of expertise from SSL industry, academia, medicine, the US government, the military and more. Diverse industry participation and feedback enabled the Task Force to produce an industry-leading document that lighting designers can use as an option in their design work. Underwriters Laboratories managed the Task Force procedures, including two Public Comment processes where lighting design professionals, facility owners, lighting manufacturers, sleep scientists, academia, scientists and other industry stakeholders from around the world provided constructive input.

While this is an evolving field, it should be emphasized that the recommendations in this document have been tested in field studies, and those studies have demonstrated that light that promotes entrainment will lead to better sleep, mood and behavior.

As a design guideline, now lighting designers and building owners and operators can pursue healthier spaces through lighting. Healthier spaces attract businesses to properties, and employees to businesses. This is due to the common understanding that spaces that are healthier are good: good for our wellbeing; good for our communities; good for business.

Perhaps a note, as this is a document published by Underwriters Laboratories. This is an optional design guideline… optional in that it’s not a UL Safety Standard. UL Safety Standards often become requirements when adopted by municipalities or states.

DiLouie: What was the general rationale for UL’s interest? Did UL do any market analysis indicating current or future adoption? Did UL see a problem that needed to be solved?

Lilien: The rationale for our involvement in this design guideline was directly related to our mission of working for a safer world.

UL employs exacting scientific processes and the highest ethical principles to help accomplish this. As technology challenges and concerns expand to include sustainability, well-being, connected technologies and security, we provide broad leadership, deep expertise and vital services to guide these transformations. Fueled by our mission of working for a safer world, we are trusted partners in solving our customers’ and stakeholders’ most critical challenges. We believe that when choices are empowered by insight and opportunity, the potential to realize responsible innovation and better living is endless. To fulfill our mission, UL delivers business solutions and our nonprofit conducts independent research and shares scientific knowledge broadly.

The opportunity here was to advance the market place’s understanding of the non-visual effects of illumination, and its impact on human circadian systems. UL does not see this document as an “end goal”; rather, we see this as a critical starting point where achieving the design goals will predictably improve building occupants health an wellbeing.

Over time, as other organization publish their positions on the science and the practice of circadian-effective lighting, the field will evolve based on deeper learning from case studies.

DiLouie: What does UL hope will be achieved with this publication?

Lilien: Through this deeper understanding of these design guidelines and the science behind them, we know that several stakeholders will see opportunities:

• Property owners will see healthier indoor spaces as an opportunity to distinguish their properties, increase property values and provide a meaningful improvement to building occupants’ lives;
• Lighting specifiers will see an opportunity to have a deeper impact on the ultimate users of the spaces that they design, and will have an opportunity to advance their careers in meaningful ways;
• Electrical contractors will see an opportunity for deeper partnerships with lighting specifiers and building owners to ensure that the designs are implemented properly, while growing their business
• Building occupants will see greater alertness, less reliance on stimulants, better sleep quality, and the resulting improvements in health.

DiLouie: Why did UL publish this guideline rather than wait for the Illuminating Engineering Society to produce an ANSI publication?

Lilien: Through the process of UL’s task force developing these design guidelines, our collaborative discussions with IES, CIE and WELL Building institute have deepened.

Through those discussions, we understand that the goals that we defined —to explore an optional design guideline that delivers benefits that are backed by scientific studies — employ a different approach and methodology. For example, IES has stated that they committed to an ANSI-based process. UL’s Design Guideline is not based on American National Standard Institute’s requirements. Multiple approaches are beneficial, and the industry should look forward to the upcoming options that other organizations provide.

While not all organizations agree, it is difficult to argue that creating a baseline for delivering more light during the day, and less light at night, is too early given the current understanding of the science.

UL looks forward to the work that associations, institutes, commercial entities and non-profit organizations can do collaboratively to advance the understanding of science-based illumination, especially as it related to human centric lighting and its impact on health and wellbeing.

DiLouie: The WELL Building Standard uses a different metric and possibly a different resulting design objective. How should designers reconcile the UL guidance with WELL?

Lilien: We believe that WELL Building Standard and UL’s resulting design approach — more light during the day and less light at night — are very consistent.

According to WELL, “WELL is a performance-based system for measuring, certifying, and monitoring features of the built environment that impact human health and well-being, through air, water, nourishment, light, fitness, comfort and mind.” Their website further states: “Light: Minimize disruption to the body’s circadian rhythm. Requirements for window performance and design, light output and lighting controls, and task-appropriate illumination levels are included to improve energy, mood and productivity.”

DG 24480 Design Guideline focuses specifically on promoting circadian entrainment with light for day-active people.

One difference is the method. By focusing on the Circadian Stimulus (CS) method, UL was able to define six specific steps to achieve the resulting design objective. These appear in the Design Guideline as a two-page “Quick Guide”.

As found on the WELL website: “WELL uses EML as a metric to evaluate the circadian impact of both natural and artificial light. Equivalent Melanopic Lux (EML) is a measurement of the effect of light on the human circadian rhythm. It is similar in concept to the more widely-used Circadian Stimulus metric, but computed in a different manner.”

DiLouie: In a nutshell, what does UL DG 24480 encourage as a guideline for designing circadian-friendly lighting systems?

Lilien: The process, perhaps oversimplified here but well thought out in the DG 24480 Design Guideline, has six steps:

1: Select a circadian-effective lighting design goal. Deliver a Circadian Stimulus of 0.3 (the rationale is found in the Design Guideline)
2. Select a luminaire type with the desired horizontal distribution. A higher vertical to horizontal ratio delivers a higher CS result
3. Select a light source Spectral Power Distribution (SPD). The amount of illumination across the spectrum of visible light in considered here
4. Perform CAD software measures of the light delivered in the plane of the occupant’s eyes
5. Calculate Circadian Stimulus (CS) using the calculator
6. Ensure that the CS is equal or greater than 0.3. If not, consider other luminaires or more local lighting near the work station

These rationale for these six steps are best understood after reading DG 24480, which is comprised of over 50 pages of worked examples, research overviews, and calculation procedures.

DiLouie: What are typical design approaches and equipment used to achieve DG 24480, and how do they different from typical current approaches?

Lilien: The approach requires the industry to not only consider the visual effect of lighting (the horizontal measure of illumination at the task level, such as a desk), but to newly consider the vertical illumination delivered to the eye.

As mentioned here, designing with knowledge of the vertical to horizontal ratio, SPD, and the resulting Circadian Stimulus are all new to this approach.

The use of a spectroradiometer capable of measuring SPD in the field is suggested here, which is also new to the lighting specifier.

The use of CAD software is a common tool for the lighting specifier.

The new practice that we have to get used to is that more lighting is required during the day, and less lighting during the night. Where a space is measured and falls short of the desired goal of 0.3 CS, the lighting designer would consider modifications to the existing system, and possibly adding layers of light. The DG 24480 Design Guideline provides direction and the scientific rationale throughout the document.

DiLouie: What are the market drivers for circadian-supportive lighting, and when is the market going to shift to these new practices?

Lilien: We already see the shift taking place.

Speaking with Gayathri Unnikrishnan, Director, Standard Development at WELL Building Institute, over 800 WELL Building projects are underway.

Since a lot of the circadian research has been conducted in healthcare facilities, we are seeing movement in healthcare spaces first.

Attending events like LightFair, it’s amazing to see how many lighting manufacturers are addressing circadian-effective solutions, or “human-centric lighting” as some call it.

We see lighting designers learning the principles of DG 24480.

We see building owners and operators seeking ways to distinguish their properties competitively wanting to learn more, and ready to consider a test.

Building owners will look for the ROI to justify the expense. As case studies are published, and the costs to implement are positively compared to the results, adoption will follow.

DiLouie: Circadian lighting may involve higher light levels than may be possible with today’s strictest energy codes. What can designers do?

Lilien: With DG 24480 Design Guideline, designers can now do a lot.

Addressing this question is rather complex, as one needs to be aware of the nature of building energy codes, how they are formed, how they are adopted, and how they are updated.

My comments here are focused on the energy codes in the 2018 IECC Commercial Electrical Power and Lighting Systems. The section of the codes your question refers to is: Interior Lighting Power Allowances, measured in watts/ft2.

Today, the lighting power allowances make no specific accommodation for projects addressing circadian-effective lighting in, for example, office buildings.

In the meantime, let’s look at the current requirements for energy conservation, as well as how exceptions to these requirements have been handled.

For office spaces, the Lighting Power Density ranges from .93 to .81 w/ft2 for enclosed and open floor plans, respectively. While my observations are over simplified, where a fluorescent space in the past might use 1.2 w/ft2 an upgrade to LED would typically reduce this 50%, to .6 w/ft2. Occupancy sensors or advanced controls would reduce this even further, say by 33% to .4 w/ft2.

Following this mathematical logic, a circadian lighting design that employs an energy-conservative approach has some room to fall within the current energy requirements.

What’s unique about DG 24480 Design Guideline is that it informs the lighting specifier how they would address solving for circadian entrainment with both a fixed, as well as a dynamic lighting system. Fixed is, for example, fluorescent lighting on a light switch. Dynamic includes color-shifting (typically 2700K to 6500K) luminaires or lamps that could be on IoT controlled systems.

In both cases, the document points out that solving for circadian entrainment using color-shifting luminaires on IoT controls is more efficient.

Regarding today’s strict energy codes not addressing circadian effective projects, my personal opinion is that this is likely to change soon. Why? With documents like DG 24480, the committees considering updates to the energy codes can now include the research approach, the findings, and the design guidelines as a factor in upcoming updates.

Just one way that this might be accomplished in the short term is for an exception allowance, like today’s code requirements make for the following project types:

• Retail spaces
• Lighting for occupants with special needs (visual impairment and other medical and age-related issues)
• Casino gaming areas
• Task lighting for medical and dental purposes
• Display lighting for exhibits in galleries, museums and monuments
• Plant growth or maintenance
• Approved because of safety considerations

Perhaps we can anticipate an addition such as: Lighting that addresses Circadian Entrainment

DiLouie: What’s in it for electrical contractors? Why should they care? Why should they get behind this?

Lilien: This is a great question.

Building owners and operators rely on their internal expertise as well as trusted partners when considering if a technology advancement is “ready” or “just a trend”.

While Return On Investment is critical to the building owner, if the service providers are not convinced that they can deliver the result, the decision maker is not going to move forward.

For new buildings, designing for circadian effectiveness will likely be adopted quickly.

For existing spaces, it’s more challenging.

While lighting designers need to take the lead and be able to ensure a prospect that their current space can be modified successfully, electrical contractors who learn about circadian-effective projects will add a level of certainty to the decision-making process.

For these firms, establishing a circadian lighting book-of-business for both new construction and retrofits will move them to the top of the list, as this reduces the uncertainty of the project costs related to delays and re-work.

DiLouie: Is there anything else that contractors should do or know concerning DG 24480?

Lilien: Other organizations have chosen to pursue an ANSI-based process for publishing new lighting standards related to health and wellbeing.

With over a century of experience in the development of more than 1,500 Standards, UL is an accredited standards developer in the US and Canada.

When the situation calls for it, Underwriters Laboratories (the not-for-profit) also publishes documents such as Outlines of Investigation (OOI), Technical Guidance Documents (TGD), Recommended Practices (RP) and Design Guidelines (DG).

DiLouie: If you could tell all electrical contractors just one thing about circadian-supportive lighting and DG 24880, what would it be?

Lilien: As a lighting industry, we have provided illumination for vision for over 100 years. Over the past several decades, we have come to know that we are under-illuminating our indoor spaces during the day, and over-illuminating them at night.

While there is certainly more for us to understand, science-based studies concur that new lighting design practices can improve human health and wellbeing today.