An investigation of atrium luminous environment: Integrating effects of surface reflective properties and shape variations.

Abstract

The luminous effects in atrium spaces illuminated by daylight are affected by the dynamic, directional characteristics of daylight and the architectural features such as fenestration systems, atrium surfaces, atrium geometries, and so on. Most previous research has avoided the directional effects by concentrating on overcast sky conditions and ideally diffuse reflectance from atrium surfaces. This study addresses and combines three interrelated factors: directionality of daylight, bidirectional reflectivity of surfaces, and atrium shape variation. Since the directional reflectance values of surface materials are least available in the literature, this research starts with exploration and measurement of selected materials representative of architectural application. Some of these measurements utilize narrow beams of plane polarized light to resolve directional attributes of specular and diffuse reflectance. Other measurements of directional reflectance utilize broad distributions of illumination such as simulated uniform and non-uniform (overcast) sky conditions. Then interior illumination distributions are investigated in simplified scale model atria constructed of measured surface materials and in several geometrical configurations. Two types of exterior illumination are used: a simulated C.I.E. standard overcast sky which is weakly directional, and the natural clear blue sky with direct sun which is highly directional. The amounts and distributions of interior illumination are investigated across the floor and up the side wall of the atria and, in some cases, further resolved into sky and internally reflected components. The model studies have successfully incorporated those three interrelated directional factors. The observed patterns of internally reflected component (IRC) change in consistent, complicated ways; the highly directional clear sky condition yielding the more varied results. The scope of these model studies are thought to encompass, in realistic fashion, the diverse range of features likely to be encountered in most atrium buildings. The results enhance understanding of luminous environments produced by daylight in atria and can be particularly useful during architects' preliminary design stage.