Tunable Lighting Put to the Test

By Craig DiLouie

Following the renovation of two floors of an existing hospital wing, the new Swedish Medical Behavioral Health Unit (BHU) opened to provide mental health services to the public. The nearly 15,000-square-foot BHU features 22 beds. ZGF Architects produced the design, which includes state-of-the-art lighting.

For the lighting, the designers wanted to blend the best of old and new based on biophilic/circadian design principles. They retained an existing outdoor space and a large skylight in the common area. They also specified downlights in BHU’s corridors and dining/activity space that provide both color tuning and dimming.

LED technology is capable of controlling the spectrum, intensity, and distribution of light in a way that is easier than with traditional fluorescent lighting. BHU’s common area lighting is programmed to change in spectral power distribution and intensity throughout the day to achieve a positive circadian and psychological response. Correlated color temperature (CCT) changes to align with a daylight cycle, ranging from as high as 6000K midday to 2400K at night. Similarly, the intensity varies from higher light levels in the morning and early afternoon and lower levels at night.

The DOE evaluated the project as part of its GATEWAY program and found some significant lessons:

• Tunable LED lighting can provide satisfactory energy savings. When intensity is reduced, energy is saved. Dimming the downlights resulted in an estimated 41 percent annual energy savings relative to non-tunable luminaires.
• Achieving circadian lighting may require higher light levels than currently recommended for visual tasks. This may result in a tradeoff in energy consumption during periods when higher light levels are needed. In this case, 19 percent more energy use during periods when a circadian stimulus was being achieved.
• Manual control may increase energy savings. The control system was programmed to enact a low intensity level at night. However, the nurses decided the cove lighting provided adequate illumination and turned the downlights off.
• Tunable systems may require more commissioning depending on the project goals. The BHU project required two rounds of commissioning to achieve the right range of CCTs and intensity levels and produce desired energy savings. For this type of control system, it is important to develop a detailed control sequence of operation (narrative) and include it in the specification.
• Regarding the circadian effect, it is important to estimate and measure spectral power distribution at expected eye locations, but it is difficult to do so for every possible combination of position, orientation, luminaire location, and surfaces and furnishings. The DOE called for new techniques to predict circadian effects during the design process. Mockups may be necessary.
• The DOE further noted that scientific evidence continues to connect tunable lighting’s health effects to proposed metrics, but no such metrics have yet been formally adopted as standards. A collaborative design approach integrating biophilic experts in the team may be beneficial.

Learn more about the BHU project here.

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Craig DiLouie, LC, principal of Zing Communications (zinginc.com), is a lighting industry journalist, analyst, marketing consultant, and author. Reach him at cdilouie@zinginc.com.