Spatial efficiency: An outset of lighting application efficacy for indoor lighting

Electric lighting plays a critical role in buildings, not only impacting the well-being, satisfaction, and performance of building occupants but also accounting for a significant portion of energy consumption. The commonly used efficiency metrics for lighting, such as luminous efficacy or lighting power density, fall short of quantifying the effective light in architectural spaces. To address the shortcomings of existing efficiency measures, lighting application efficacy that characterizes the efficient delivery of light from the source to the target should be utilized. Lighting application efficacy can account for efficiencies in temporal, electrical, sensory, and spatial dimensions. This study outlines a method to quantify the spatial efficiency of electric lighting in buildings. As proof of concept, simulated spatial efficiency data are analyzed for two targets (horizontal work plane level and occupant field of view) based on the primary characteristics of the built environment and lighting systems. The findings indicate that design variables (e.g., room size, luminaire distribution type, reflectance of the surfaces, and field of view) can significantly affect the spatial efficiency of lighting in the specified settings. Therefore, spatial efficiency values can exhibit considerable variation among distinct lighting systems and architectural spaces and should be customized to suit the unique requirements of each design setting. Future research will investigate and establish the complementary components of the lighting application efficacy framework.