The Flow of Light into Buildings

A knowledge of angular relationships is essential for studying the view through a window and for calculating daylight factors. A perspective drawing contains information about the various angles subtended at a chosen view-point and thus lends itself to the study of natural lighting. However the traditional method of specifying daylight—in terms of a horizontal working plane—can give a misleading impression of the lighting conditions, which depend largely on light reaching vertical surfaces. Similarly the advent of luminance design in artificial lighting has created the need for some three-dimensional concept to replace horizontal illumination as a criterion of adequate lighting. Illumination can be analysed in scalar and vectorial terms. The calculation of scalar and vector illumination is discussed; for natural lighting each can be determined from perspective drawings. For artificial lighting the scalar illumination can be calculated from British Zonal data; this provides an index of adequacy for many li...