Museums require a stable lighting environment suitable for exhibits as well as visitors throughout the exhibition areas. This paper suggests a lighting design method for exhibition spaces in museums that modulates the shape of toplights, affecting the balance of natural light within the space. Both scale model tests and simulations using the RADIANCE software were performed and their datasets were compared, in a complementary manner, to confirm the validity of this method. The results were then applied to an existing museum — the Seoul Museum of Art in the Republic of Korea — to confirm the performance of the method in modeling an actual environment. By modulating and controlling the parameters, the appropriate dimensions of the monitor-shaped toplight for the museum were determined. The experimental results of this study suggest that the daylighting simulation method, if properly modulated, can become an integral part of the architectural design that can produce a predictable lighting environment for a museum.