Luminous intensity solid of tubular light guide and its characterization using “asymmetry parameter”

The luminous intensity solid of hollow light guide is determined using an extended HOLIGILM solution. The solution concept enables to simulate luminous intensity solids for various light guides and sky luminance patterns. Angular distribution of light emitted from bottom interface of the light guide strongly depends on how the illumination system is designed. Any beam undergoes many reflection events which influence significantly its direction below the optical interface. As a consequence, the computed luminous intensity solid may show many peak during sunny days. After interaction with tube the light beams suffer from imperfect reflections resulting in non-uniform luminous intensity solid even if the sky luminance is constant. The directionality of the light below the pipe is characterized by asymmetry parameter which is a cosine-weighted integral of luminous intensity. Such a single-value can serve as supplementary parameter that quantifies a measure of downward luminous emissions.

► Luminous intensity solid of tubular light guide has a complex form under sunny conditions.
► Luminous intensity solid under overcast conditions is a function of reflectance of the inner surfaces of the light tube.
► The concept of asymmetry parameter typically applied in optics of random media is applicable in modeling the light-guides.
► Asymmetry parameter is used to quantify a portion of luminous energy propagated downward.