Spatial and spectral illumination design for energy-efficient circadian lighting

Daily light-dark patterns incident on human eyes play an important role in maintaining a healthy circadian rhythm. The lack of daytime light in indoor spaces could negatively impact the occupants’ health and well-being in the long term. Therefore, applying circadian lighting in certain built environments is attractive. In this work, we introduce innovative methods for circadian lighting design and investigate the potential of efficacy improvement by comparing these methods with traditional lighting design approaches. For the spatial aspect, we show that the regular lighting design approach focusing on horizontal workplane illuminance could lead to a very inefficient delivery of indirect corneal illuminance compared with the proposed method of distributing initial flux to a highly reflective room surface; for the spectral aspect, it is shown that the traditional approach of pursuing high luminous efficacy could potentially lead to the worst-case scenario for circadian efficacy based on a four-component color-mixing analysis. Two leading spectral sensitivity models for the circadian system (i.e., the CLA model and the EML model) are compared, each of which leads to different trends of spectral circadian efficacy versus color temperature but the same strategy for spectral optimization. Based on the analysis in both the spatial and spectral aspects, a framework of efficient circadian lighting solutions is proposed to guide new good lighting design with health benefits. It is shown that the proposed new approaches can potentially improve the overall circadian lighting efficacy by up to 3.6 times. •A framework of energy-efficient circadian lighting solutions is proposed.•Overall efficacy improvement potential up to 3.6 times is demonstrated.•Indirect lighting can be very efficient in delivering corneal illuminance.•Two leading spectral sensitivity models for the circadian system are compared.•Traditional spectral optimization method may lead to a low circadian efficacy.