Daylight guidance systems are quite effective devices. Such systems are able to reduce the artificial lighting costs of a building and improve employees’ work conditions inside. In this paper, a comparative thermal analysis of two types of natural roof lighting systems is presented. The analysis has been performed for a roof equipped with a daylight guidance system, being a more contemporary type of lighting, as well as for a roof with clerestory, which is a more traditional and widespread type. The thermal analysis is performed by numerical method featured by two computer programs – NASTRAN and TEPL, making it possible to increase reliability of the results. The analysis shows that application of daylight guidance systems improves thermal performance of a structure and increases the value of thermal resistance of structure’s envelopes. Thus, one more benefit of applying daylight guidance systems is revealed.