Daylight is important for a human organism mainly in the physiological and psychological respect. These days, however, the economic aspect is also becoming a non-negligible parameter. Due to the lack of daylight eye strain occurs that may lead not only to eyesight damage, but also to various related health disorders studied by numerous experts. In places not directly neighbouring on the exterior environment a suitable means of lighting are daylight guidance systems which may transmit light over long distances. Their installation belongs to investments with high financial demands; therefore, adequate attention should be paid to the optimisation of their design with respect to the interior environment resulting in the maximum effectiveness of the designed installation even without any contact with the exterior environment. At the same time, a light guide should be designed to eliminate thermal bridges and thus undesirable manifestations of condensation on the inside surfaces of structures.