In Seattle, Washington, the new Swedish Medical Behavioral Health Unit (BHU) in the Ballard neighborhood serves patients dealing with mental health conditions. ZGF Architects and their design collaborators supervised the design and building of the new BHU, including the design of the lighting. The architects wanted the lighting to help create an environment that connected staff and patients to nature and offered the beneficial health effects of light.
As part of this GATEWAY evaluation, ZGF invited the U.S. Department of Energy Solid-State Lighting program to document the performance of the LED lighting systems. For the DOE, this project was an opportunity to study how LED systems deliver value to end users, and how these
systems can be enhanced to offer increased efficiency and improved quality.
ZGF design team created the lighting system for the corridors and dining/activity space to operate according to a daily
schedule. The schedule included a shift in the spectral power distribution (SPD) of the downlights throughout the day. The correlated color temperature for the lights ranged from 2400 K at night to 6000 K midday. This color variation is analogous to the color variation of sunlight throughout the day. The schedule also varied the light intensity levels. Lower levels of light were delivered through the evening and night, and higher levels were provided in the morning and early afternoon.
In May 2016, an initial set of SPD and illuminance measurements were taken. The measurements revealed that the design team did not achieve their goals. The schedule delivered higher than desired illuminance levels and showed a constricted SPD range. The designers went through a second and third round of commissioning to meet the biophilic and circadian design goals.
Optimizing a tunable white lighting system for biophilic and circadian goals, even on a small-scale, necessitates a thorough understanding of the latest research related to circadian photobiology and an understanding of LED technology. Unfortunately, the commissioning agents may not have the proper meters needed for measuring both the SPD and illuminance.
Detailed Specification of Control Sequences and Outcomes Required
The lighting designers had to develop a detailed specification of the desired control sequences and outcomes because estimating and measuring the SPD of light at expected eye locations is important for achieving circadian design goals. However, so far, there is no easy way to estimate the effects at possible eye positions in an architectural space.
The DOE also points out that scientific evidence relating the medical effects of tunable lighting in architectural spaces to emerging lighting metrics has not been established. Furthermore, the DOE notes that the metrics themselves have not been standardized for use in lighting. The testing revealed that this tunable system increased estimated annual energy usage by 19%.
Biophilic and Circadian Design Goals Needed System that Could Vary Intensity and Spectrum
This application with biophilic and circadian design goals needed a tunable lighting system that could vary both intensity and spectrum.
They found that the reduced intensity levels specified for extended periods of the day and night from the downlights offered an estimated annual energy savings of 41% compared to a non-tunable downlight system with the same number of luminaires.
However, when compared to a non-tunable system designed to only meet visual task illuminance criteria using half the quantity of luminaires, the tunable system increased estimated annual energy usage by 19%.
The DOE noted that achieving design goals related to circadian and other biological and behavioral effects of lighting
sometimes necessitates higher intensities than those recommended for visual tasks. Such intensities may increase the energy use of lighting during the hours when those high illuminances are needed.
During this project, 74% of the estimated annual energy use of the tunable lighting system occurred in the six hours each day when the control settings were created to achieve the desired circadian stimulus. While the energy reductions that occur during the hours when the lighting was dimmed to lower intensity levels may offset the increases during the high-intensity hours, it may be difficult to justify the increased cost and complexity of tunable systems while the evidence of the non-energy-related benefits is still not fully established.
Some Manual Control Helped Save More Energy
The DOE noted that giving the building occupant some degree of manual control can increase energy savings. The original specification for the downlight system that was first programmed into the automatic controls kept the downlights at a dimmed level during the night. However, the nursing staff decided to use the manual dimming option to turn off the downlights at night based on their observation that adequate lighting from the cove system was provided in the space during the low-usage nighttime hours.
Allowing such manual user behavior reduced system energy use and was subsequently programmed into the automatic controls. The demonstration found that commissioning of the tunable systems remained a challenge given current field practices and capabilities.
Field commissioning today often requires establishing scene settings based on control settings and/or visual assessment of the scenes, rather than confirming with measured spectral and illuminance data.
They also found that developing a detailed specification of the desired control sequences and outcomes including spectral distributions, illuminances, circadian, and other metrics early in the design process can help identify potential shortfalls with the specified control solution, and can make the commissioning process more efficient. While the initial control specification for this project was more detailed than usual, the
resulting variations in commissioning, measurement, calculation, and system adjustments showed the
need for even more specificity in the original specification.
No Easy Way to Estimate SPD at Possible Eye Locations
They also noted that estimating and measuring the spectral power distribution of light at expected eye locations is important for attaining circadian design goals. However, there is currently no easy way to estimate the SPD at possible eye positions in an architectural space. Notably, SPDs at eye locations can vary based on position, viewing direction, furnishings, architectural surfaces, and the location of luminaires.
Scientific evidence proving the medical effects of tunable lighting and the related lighting metrics have not been established.
Overall the demonstration project found that future projects would greatly benefit from design and research teams with expertise in lighting, biophilic design, and medical research.