In addition to enabling vision, light-dark patterns reaching the back of our eyes are the major synchronizers of circadian rhythms to the local position on Earth. Light can also elicit an acute alerting response in humans similar to a cup of coffee. Since the discovery of the intrinsically photosensitive retinal ganglion cells (ipRGCs) in 2001, a series of studies depicting how this novel photoreceptor interacts with the classical rods and cones to convert light signals into electrical signals to the biological clock, a process called circadian phototransduction, have been made available to the lighting community.
The scientific community – while not necessarily in agreement on the metrics nor the neurophysiological details of circadian phototransduction – does agree that bright days and dark nights are essential for maintaining synchrony between the external environment and the internal biological master clock in our bodies. That synchrony, in turn, results in better sleep, health and wellbeing. As such, there is a growing call for application engineers and lighting designers to begin translating this scientific knowledge from controlled laboratory conditions to real-world applications.
This is not to say that there won’t be challenges. For starters, we need more light to affect our biological clock than we need for vision, and our beloved Vλ does not represent the spectral sensitivity of the circadian system. (Footnote: as a reminder to readers who may not be familiar with it, Vλ is the spectral sensitivity function that is used to define the lumen).
The timing and duration of light exposure are also critical for the circadian system, so knowing when to deliver and when to remove bright light in the environment becomes essential. Additionally, glare, energy consumption, aesthetics, and cost remain critical components of sustainable, effective design.
Through collaboration, outside-the-box thinking, and a clear understanding of the design factors that are most important, circadian-effective lighting can be achieved while maintaining established design and energy efficiency standards and without being impossibly complicated. Exemplary design projects can help grease the gears of this process and guide the way for the design community. The recently completed IESNYC Lumen Award-winning lighting design for the flagship office of a financial services firm located in New York City serves as one such project that is a significant step towards the normalization of circadian-effective lighting in commercial office spaces.
The Design Process and its Challenges
It began like many other large LEED-Gold projects: corporate standards required Lighting Power Densities (LPDs) at least 35% below ASHRAE while maintaining 30 fc on the workplane using 3500 K correlated color temperature (CCT) lighting. Mockups were reviewed and approved at the conclusion of Design Development for the two signature lighting elements in the workspaces: a) the backlit, faceted ceiling at the trading floors, and b) custom 30”×30” luminaires utilized throughout the project.
At the beginning of the Construction Documents phase, however, the client pulled the lighting designers aside and asked what it would take to incorporate “circadian lighting” into the approved design.
The lighting designers investigated evidence-based circadian lighting strategies and drafted a feasibility report determining that the design targets for circadian effective light could be achieved while maintaining the energy efficiency, visual comfort, and aesthetic requirements of the project. However, deviations from the corporate standards for light level (30 fc) and CCT (3500 K) would be required. The designers also insisted that a team of light and health scientists serve as technical partners to verify that the proposed design would deliver the targeted circadian-effective light. For this project, the circadian stimulus (CS) metric was utilized. For more information go to CS Calculator (2.0) | Light and Health Research Center (light-health.org)
Occupant schedules in the space posed a design challenge. Because of the client’s hours of operation, some workers arrived in the office as early as 6:00 am while others worked as late as 10:00 pm. The goal was to deliver high circadianeffective light in the morning (circadian stimulus (CS) = 0.3 at eye-level starting at 6:00 am) and gradually transition, by changing light level and CCT, to a circadian-ineffective light (CS = 0.1 at eye-level) after 10:00 pm while maintaining enough illuminance for visual performance. See Table 1.
The technical team performed on-site measurements including vertical and horizontal illuminance, CS, and spectral power distribution of the various light settings. This revealed a slight spectral shift of the LEDs due to interreflected light, which reduced the predicted CS values and required an increase in light levels during commissioning to compensate; underscoring the importance of performing site measurements.
• Diligence and attention to detail are needed to achieve the design targets, not only in computer simulations, but after the installation is complete.
• Do not rely on computer simulations alone if you want to make sure your CS design targets are achieved in the field.
• Implementation of circadian-effective light in the field can be done without sacrificing energy efficiency, visual comfort, and aesthetics.
• The collaboration between owners, designers, and scientists is key to success.
In summary, circadian-effective lighting should not be a luxury item and is achievable through creative problem-solving, collaboration, and a clear understanding and communication of the value of light to the owners and the users of the space. The more projects we have like this one, the more mainstream these ideas are going to be.
Acknowledgements: The authors would like to thank their colleagues for a successful collaboration on the project. The technical team: Mariana G. Figueiro, PhD and Kassandra Gonzales, and the design team: Meryl Sell, Maggie Judge, and Jackson Ning.
This article was originally featured in the August issue of designing lighting (dl)