The make a decision for building remodeling, the economical value of the remodeled building should be analyzed and existing situation of the building system should be checked. For the energy issues related to the building remodeling process, careful diagnosis and re-designs of existing system should be proposed. In this research, the luminous environment for Seoul K Co. headquaters and Seoul S hotel were measured and then the re-design processes of building illumination systems were researched. With measured illuminance quantities of there cases, computer simulations for the existing situation and re-design were conducted.