## 4 Conclusions  
Optimization of WWR offers a balanced solution to the contradictions involved in selecting an appropriate WWR in future building design to sustain occupants' thermal comfort with the least amount of heating, cooling, and lighting energy. Although increasing the efficiency of active technologies impacts the passive approaches used in buildings, there has been minimal focus on this topic in the literature. Hence, the aim of this study is to investigate the effects of enhancing the efficiency of lighting systems on the optimum WWR of residential structures in the city of Amman in Jordan. Additionally, this research intends to emphasize the significance of these types of studies on enhancing 'energy-efficient' buildings. The results are based on an intricate simulation of a standard residential building in Jordan by utilizing the energy simulation software DesignBuilder. Simulations were performed on 11 distinct WWRs ranging from 0% to 100%, with increments of 10%. The results generated by the simulation demonstrate the impact of enhancing the efficiency of the lighting system on the window size and emphasize the significance of combining optimum passive strategies with the most efficient active technologies when designing the building to maximize the overall energy savings while minimizing costs. The findings refute the popular belief in terms of increasing size of windows to confirm that the building has enough lighting and using heating to lower the overall energy consumption, due to the variations in the overall site energy in different WWR scenarios that suggest that the highest amount of energy was used in the 0% scenario rather than the 80% scenario. Nevertheless, a low percentage of WWR caused the overall demand for energy to increase up to 30%. The findings offer useful guidance that stresses the significance of enhancing the efficiency of lighting systems on reducing the size of windows. The results clearly revealed that there were more significant changes in terms of the space-cooling energy in comparison with the lighting and heating energy. Conversely, significant changes in lighting energy only occurred when transitioning from the 0% to the 20% scenario, but then stayed largely constant for the remainder of the scenarios. A factor that accompanies natural light is solar heat radiation, which can lead to considerable increases in terms of the building's cooling and heating loads. Hence, it is necessary to strike a balance between solar heat and light gain to completely exploit solar energy with no reverse impacts. LED with linear control can be considered a cost-effective lighting strategy, which has been demonstrated to be effective in minimizing the energy consumed and therefore the volume of CO2 emitted. This study proposes that the typical WWR for residential buildings containing a LED lighting system could be lowered to the range of 25-30%, which is lower than the maximum WWR of 40% stipulated in the ASHRAE standard. In addition, this study recommends that energy-simulation software is essential for use in the building designing process to precisely determine the WWR for the residential structure, between 25% and 30%, since changes made to an individual element can affect different associated elements, as quantitative strategies are limited in the settings and presumed properties of the models in this work, in the context of the Jordanian climate, and using local construction materials. Finally, although the optimum WWR can range between 25% and 30%, it still provides a good indication of the reduction that can be achieved by enhancing the efficiency of lighting systems, because it is critical for the sustainability of future projects that recommendations are provided to determine the optimal WWR for minimizing cooling and heating loads, as well as ensuring an appropriate level of lighting. Additionally, this research intends to emphasize the significance of these types of studies on enhancing 'energy-efficient' structures.