Beyond Energy Efficiency: What Healthcare Sustainability Should Measure Next

Healthcare buildings must reduce operational carbon without treating human experience as a secondary outcome. All-electric systems, efficient envelopes, and certification are meaningful achievements. They do not, on their own, describe the light reaching occupants' eyes across the day, the glare or visual conditions they experience, or whether evening and nighttime lighting supports rest.

The design problem is not energy versus health. It is how to evaluate energy, carbon, visual performance, and time-varying light exposure together, then communicate the trade-offs clearly enough for design teams, owners, clinicians, and occupants to understand.

A recently completed all-electric, LEED Gold outpatient oncology center in Southern California offers a useful example. Public project materials describe a low window-to-wall ratio and high-performance glazing as envelope strategies, while also documenting natural light in treatment suites, abundant daylight in imaging areas, exterior connections in radiation-treatment spaces, and a net-zero target.

Those facts do not support the claim that daylight was simply ignored. They reveal a more useful question: what performance information is missing from public sustainability narratives? The available project descriptions do not report eye-level melanopic equivalent daylight illuminance, exposure by time of day, glare, or post-occupancy circadian outcomes. Absence from public documentation is not proof that these analyses were omitted. It does mean that a reader cannot evaluate them.

Illuminance on a horizontal workplane remains important for visual tasks, but it is not a complete proxy for non-visual light exposure. CIE S 026/E:2018 provides SI-compliant alpha-opic quantities, including melanopic equivalent daylight illuminance, for describing retinal photoreceptor stimulation associated with ipRGC-influenced responses. The standard is a metrology framework, not a clinical outcome model or application-specific mandate.

An expert consensus published by Brown and colleagues in 2022 recommends, for healthy adults, at least 250 lux melanopic EDI at the eye during daytime when possible, less than 10 lux during the three hours before habitual sleep, and less than 1 lux in the sleep environment. These are evidence-informed targets rather than universal healthcare codes, and patients, shift workers, clinical tasks, age, medications, safety, and care schedules may require different strategies.

Healthcare evidence supports attention to light timing and spectrum, but it does not justify sweeping guarantees. A 2024 systematic review of 21 healthcare-lighting studies found promising relationships among daylight, timed electric light, sleep, mood, and circadian alignment, while also reporting heterogeneous interventions and outcomes. Earlier systematic work similarly found that light can improve some sleep-related outcomes, but the strength and consistency of evidence vary by population and protocol.

A 2025 study of 87 hospitalized cardiology patients associated dynamic lighting with a 160-minute advance in rest-activity phase, 66 additional minutes of overnight sleep, and improved perceived alertness. The authors also called for confirmation in larger and more diverse clinical populations. That is the appropriate level of claim: light is a modifiable environmental exposure with credible mechanisms and encouraging field evidence, not a substitute for clinical care and not a guaranteed recovery intervention.

Circadian-supportive design can increase electric-light demand if it relies only on higher light levels. U.S. Department of Energy studies show why distribution, spectrum, daylight, controls, surface reflectance, glare management, and cooling loads must be evaluated as one system. Better optical distribution and targeted eye-level exposure can reduce the need to flood horizontal surfaces with unnecessary light.

For healthcare projects, a stronger performance brief would report annual daylight and glare, vertical photopic illuminance, melanopic EDI by time and occupied position, lighting and cooling energy, nighttime safety lighting, control sequences, commissioning results, and post-occupancy feedback. The point is not to maximize one metric. It is to make competing needs visible before they become operational problems.

UL DG 24480 is a voluntary design guideline for promoting circadian entrainment with light in day-active people. It should not be described as a mandatory code. WELL also provides circadian-lighting criteria, while CIE S 026 supplies a common measurement language. These resources can strengthen project briefs, but their application still requires judgment, verification, and a clear statement of who the lighting strategy is intended to support.

A sustainable healthcare building should be able to explain both what it saves and what it provides: carbon and energy reductions, visual quality, access to daylight, time-appropriate light exposure, operational flexibility, and evidence from use. Certification can organize part of that work, but transparent performance reporting makes the design accountable.

The next step is not to choose between efficient buildings and healthy buildings. It is to stop treating those outcomes as separate ambitions.

Brown, T. M., et al. (2022). Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults. PLOS Biology, 20(3), e3001571. https://doi.org/10.1371/journal.pbio.3001571

Commission Internationale de l'Eclairage. (2018). CIE S 026/E:2018: CIE System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light. https://doi.org/10.25039/S026.2018

Hadi, K., Du Bose, J. R., and Choi, Y.-S. (2019). The effect of light on sleep and sleep-related physiological factors among patients in healthcare facilities: A systematic review. HERD, 12(4), 116-141. https://doi.org/10.1177/1937586719827946

Hosseini, S. N., Walton, J. C., SheikhAnsari, I., Kreidler, N., and Nelson, R. J. (2024). An architectural solution to a biological problem: A systematic review of lighting designs in healthcare environments. Applied Sciences, 14(7), 2945. https://doi.org/10.3390/app14072945

Dunn, A. S., Fastman, B. R., Weinberg, A., et al. (2025). The impact of dynamic lighting on sleep timing and duration for hospitalised patients. Journal of Sleep Research, 34(6), e70041. https://doi.org/10.1111/jsr.70041

U.S. Department of Energy. (2023). Daylighting and electric lighting integration: Research on lighting energy and circadian-effective design.

Underwriters Laboratories. (2020). Design Guideline for Promoting Circadian Entrainment with Light for Day-Active People (DG 24480).

Public owner and architect project briefs for the completed Southern California oncology center were used to verify the case-study claims.