Influence of Varying Electric Light Distribution on Melanopic Equivalent Daylight Illuminance and Lighting Energy Use

Abstract: Human beings in modern society spend more than 90% of their time indoors to live, work, and socialize. To improve health, quality of life and task performance, integrative lighting is designed to give the right light at the right time at the eye to stimulate circadian entrainment. Current designs for integrative lighting consider rooms as black boxes, overlooking the contribution of daylight to the non-visual stimuli. To meet recommended values of circadian illumination on the vertical, the luminous power output must be three times higher than that needed to meet visual requirements, making it critical to implement daylight to save energy. This study investigated the impact of direct and direct-indirect distributions of electric light combined with daylight on horizontal illuminance, vertical illuminance, melanopic equivalent daylight illuminance, and energy use in a mock-up office in Lund, Sweden. On-site technical measurements, observer-based tests and simulations were carried out to collect data. The on-site measurements were used to calibrate the Rhinoceros 3D and Grasshopper model. Field tests with subjects were carried out to understand whether different lighting scenarios could ensure similar visual performance. Further lighting scenarios with different CCTs and view directions were tested using LARK 2.0 to determine which of the scenarios could reach the visual and non-visual requirements in the most energy-efficient way. The results showed that both direct and direct-indirect electric lighting perform similarly in terms of visual perception, alertness/sleepiness, and cognitive performance. Average horizontal illuminance exceeds visual requirements for all the lighting scenarios, but the non-visual requirements were never achieved with only electric light. Most of the circadian illumination on the vertical is provided by daylight as melanopic equivalent daylight illuminance exceeds non-visual requirements under a clear sky for most of the year. Overall, simulated results for direct electric lighting yielded a higher activation state in people for all the lighting scenarios.