Enhancing the Spatial Visual Brightness of Multi-Stories Underground Space by Optical Material Integrated Daylighting Wells

The purpose of this study is to solve the problems of underground space lighting, such as insufficient lighting in deep areas and the insufficient use of daylight, and to propose a new type of underground space daylighting wells integrating optical materials to optimize the distribution of daylight in the underground space, thereby enhancing the perceived brightness for users in underground levels. After theoretical analysis, an optical material with light deflection is designed. And the performance of three different daylighting well designs integrating this optical material was compared with conventional wells and optimized accordingly. The experiments were carried out in an artificial sky platform by means of a scaled-down physical model, using Lav, B40 (average luminance of horizontal band width 40° centered on the normal view height) as the evaluation index of spatial visual brightness, and comparing the light-gathering effects of different forms of daylighting wells with the spatial visual brightness data. The results show that: The integrated optical material improves the spatial visual brightness of underground space by 40% ~ 60% compared with the through-well, in which the inverted cone daylighting wells in the first basement level have a better collection effect, and in the second and third basement levels away from the skylight, the closer the plane size of the daylighting wells is to the size of the skylight, the better the dispersion of the daylight is. It is concluded that: (1) daylighting wells integrating optical materials have significant lighting optimization effect in underground space, which can provide users with circadian rhythm sensation and reduce the energy consumption of artificial lighting; (2) the form of daylighting wells has a greater impact on the optimization of the light environment in underground space, that is preferable to adopt inverted cone form in the basement floor close to skylights, and it is preferable to use daylighting wells near skylight dimensions in the basement floor far away from skylights.