This article discusses the performance of a new skylight for standard classrooms at the Egebjerg School (Denmark), which was built ca. 1970. This building underwent important reforms under a European project to which the authors contributed. This research aimed to create a new skylight prototype that is useful for several schools in the vicinity, since there is a lack of educational facilities. The former skylights consisted of plastic pyramids that presented serious disadvantages in terms of sustainability matters. During the design process, the priority changed to studying the factors that correlate daylighting with energy and other environmental aspects in a holistic and evocative approach. Accordingly, the new skylight features promote the admittance and diffusion of solar energy through adroit guidance systems. In order to simulate different scenarios, we employed our own simulation tool, Diana X. This research-oriented software works with the effects of direct solar energy that are mostly avoided in conventional programs. By virtue of Lambert's reciprocity theorem, our procedure, which was based on innovative equations of radiative transfer, converts the energy received by diffusive surfaces into luminous exitance for all types of architectural elements. Upon completion of the skylights, we recorded onsite measurements, which roughly coincided with the simulation data. Thus, conditions throughout the year improved.Sustainability 2019, 11, 5878 2 of 14 the factors that were correlated with light and energy dispositions, as well as other aspects such as ventilation and insulation. Many architectural designs pass for sustainable if they attain thermal regulations alone, even at the risk of subsequent energy waste in lighting devices and visual or physical discomfort. On the other hand, large glazed areas allow for more daylight into a space, but they often generate excessive heat gains or losses, which increases air-conditioning or heating loads [2]. Accordingly, the proposed new skylight improves the possibility of capturing solar energy in winter, and at the same time, internal louvers produce a uniform diffusion of light through the adroit guidance of impinging radiation.Our participation in an international design team, which was formed from experts from various disciplines, was pivotal in the study of different solutions for such skylights, taking into account the possibility of direct sunlight and comparing climates as diverse as those of Egebjerg (Denmark) and Seville (Spain). We observed through our research an apparent contrast: in less sunny climates, there seems to exist a demand for the admittance of solar radiation irrespective of potential disadvantages, and therefore it is a requirement for future designs. On the contrary, users from southern Europe tend to neglect this attitude, avoiding sunlight if possible [3].The proposed new "lantern" should overcome these constraints of obsolescence and environmental inefficacy, providing better performance. Some of its main features are a vertical south-o...