Dec 11, 2020

Circadian Lighting Recommendations Yield Potential Energy ImpactsA Pacific Northwest National Laboratory (PNNL) study, funded by the U.S. Department of Energy evaluated the potential energy impacts of circadian lighting design recommendations detailed in WELL v2 Q2 2019, UL Design Guideline 24480, and Collaborative for High Performance Schools Core Criteria 3.0. Published in the journal Energy & Buildings, the study found significant increases in indoor light levels and corresponding lighting energy use as the result of meeting current circadian lighting design recommendations.

An open office and a classroom were modeled, with the luminaire lumen output, spectral power distribution, surface reflectance distribution and desk orientation varying between the simulations in order to explore the magnitude of the different parameters. The authors found that meeting current IES illuminance recommendations did not satisfy existing equivalent melanopic lux and circadian stimulus values for any of the office and classroom circadian lighting recommendations. In some cases, meeting the circadian metric recommendations required an average illuminance that was more than double the IES recommendations, which may negatively affect lighting quality and increase energy use.

Using results from the two models and 45 unique simulation conditions, the study estimates that lighting energy use may increase by 10% to 100% because of the higher luminaire light levels used to meet the circadian lighting design recommendations listed in current building standards.

Further research may show more efficient ways to meet design recommendations through varied light distribution or optimized spectral characteristics, as well as advanced control systems. Until circadian lighting design metrics and effective delivery of light stimulus are better understood in realistic settings with recognizable health and well-being benefits, the tradeoffs between design recommendations and energy efficiency goals cannot be fully expressed.