Dynamic Simulation on Eye Exposure of In-Vehicle Daylighting in Urban Environments of China

Light has a profound non-visual impact on the human body. It affects people’s mood, alertness, endocrine and circadian rhythm. Most non-visual effects studies focus on built environment. Yet, the non-visual effects of in-vehicle lighting have rarely drawn scholarly attention. Theoretically, by changing the transmittance and reflectance of the windshield, or adjusting the luminaires in vehicles, the physiological and mental state of the driver and the passengers can be intervened. The paper carries out series of dynamic daylight simulations in multiple categories of urban environments in China, summarizes the eye exposure characteristics of in-vehicle daylighting, and proposes new suggestions regarding the lighting design in vehicles.The main results can be summarized as follows: (1) The M/P Ratio, which represents the relationship between the non-visual melanopic illuminance and the visual photopic illuminance, of the in-vehicle daylighting has an average of 1.12 for clear sky, while 1.07 for overcast sky. (2) The back seat passengers receives significant lower eye exposure compares with the driver and front seat passenger when looking ahead. However, if the back seat passengers look outside the side windshield, the eye exposure they receive is mostly higher than that the driver and front seat passenger receive. (3) The floor area ratio (FAR) of the urban environment and the facing direction of the vehicle have an impact on the eye exposure of in-vehicle daylighting. The higher the FAR, the lower the non-visual effects. Facing north receives the least amount of in-vehicle daylighting. (4) The in-vehicle daylighting eye exposure differs significantly throughout China. Of all the seven typical cities selected in the study, annual in-vehicle daylighting resources show the following order: Shenzhen > Lhasa > Kunming > Beijing > Shanghai > Harbin > Chongqing.