The objective of the work was to evaluate the impact of lighting energy savings on global energy consumption in office buildings. This evaluation comes from an integrated approach combining the daylighting and the thermal aspects, The study presented here is based on simulation results. Several facade configurations have been modeled, for the four main orientations and three combinations of internal wall reflection coefficients. These simulations were performed by coupling a daylighting simulation tool (ADELINE) and a dynamic thermal simulation software (TRNSYS). These simulations allowed us to determine the main parameters playing a rule on lighting consumption. We learned that daylighting can reduce artificial lighting consumption from 50 to 80%. The global primary energy saving coming not only from the reduction of the lighting consumption but also from the reduction of lighting internal loads could then reach 40%, for a type of glazing usually used in office buildings.