Sky classification respecting energy-efficient lighting, glare and control needs

Most sophisticated energy trade-off programs, glare studies, and energy-efficient daylighting or supplementary lighting design methods need a set of sky luminance patterns which could characterize the typical changes of exterior conditions. In every climate zone a general year-round weather pattern exists and seasonal changes produce a certain probability in the frequency of often occurring skies under definite insolation circumstances. Such sky frequency occurrence can be expressed and visualized in a parametric ''P-G-D'' diagram defined by the ratios of global, diffuse and/or horizontal direct illuminance normalized to extraterrestrial illuminance, if these illuminances are available, e.g., measured hourly or higher frequency steps for a particular locality such as for the IDMY station, a monthly or yearly classification of illuminance conditions and sky types is possible. The occurrence frequency is expressed by the number of cases in the square elements/bins of the P-G-D diagram. When this selection is clone within a small range of solar altitudes, a sky cluster system results suggesting the influences of turbidities with light diffusion-transparency reflection interaction in/on clouds. These influences are interrelated with the uneven space distribution of various cloud types on the sky vault which are detectable by scanning luminance measurements. The indicatrix and gradation function analysis can help in the classification process and reveal basic functions for modeling standard skies.