Understanding the effect of daylight on circadian rhythms through High Dynamic Range (HDR) measurements and simulations

Abstract

A growing body of research suggests that the built environment affects the circadian rhythms of building occupants inhabiting indoor spaces. This stems from the fact that the average modern human being spends about 90% of their lives indoors, which presents a need for architectural design to take into consideration how indoor spaces are able to support human health and well-being. Having a means to predict melanopic light levels through digital simulation will greatly facilitate the conversation of how design choices affect indoor circadian entrainment. LARK is a multi-spectral lighting simulation tool that can simulate indoor circadian lighting. It was developed in 2015, which makes it a relatively new tool and it is still under development. Validation is required to assess its accuracy in simulating the spectral qualities of the sky and indoor material spectral properties to give a quantitative value of circadian entrainment. This thesis compares real-world measurements with simulation results to assess LARK’s circadian lighting simulation capabilities of indoor environments and identify shortcomings that require further development. Field measurements of the spectral characteristics, Correlated Color Temperature (CCT), and photopic lux of the sky and indoor data collection site are taken. The Equivalent Melanopic Lux (EML) values are derived from spectral measurements. Year-long measurements recorded one day a month between 9:00 am to 5:00 pm are analyzed to understand the dynamic patterns of photopic and melanopic daylight availability. The field measurements also serve as inputs for LARK simulation. Comparative analysis of the simulation results against measurement values shows that LARK performs well in predicting melanopic light levels under clear sky conditions with high CCTs, but discrepancies start to arise for skies with cloud cover and low CCTs. False color analysis of the sky luminance distribution shows a difference between the LARK simulation sky model and real-world skies. This highlights a need for sky models that are better able to represent the full spectral characteristics of real-world skies as it affects the resulting simulated EML values. With further validation and development, LARK has the potential to be extensively utilized by researchers and designers to identify architectural design strategies that can satisfy both visual and circadian needs of occupants in indoor spaces.