HOLIGILM: Hollow light guide interior illumination method – An analytic calculation approach for cylindrical light-tubes

A physical model for interior illuminance calculation HOLIGILM applied to cylindrical skylights was developed. Based on the ray-tracing between the diffuser of a tubular skylight and the sky vault including the Sun, the light transmission coefficient of the cover dome and of the interior diffuser with the high light-guide reflection, as well as taking into account the geometry of the interior, the resulting illuminance of the working plane can be analysed. As the model is strictly physical it allows to study influences of optical properties of tubular skylights (dome, tube and diffuser) on the interior daylight illuminance distribution specifying the luminance distribution on the hollow light-guide diffuser. The standard sky luminance distributions adopted ISO 15469:2004 and the new solar luminance and constant were included into the evaluation concept of tubular skylight. In addition to the original formulae some practical examples of the predicted illuminance on the working plane are also presented in this paper.