A blind system for window glass has been designed and manufactured as a CapStone Design project at Seoul National University of Science and Technology. This system automatically controls the interior illuminance to maintain a uniform temperature. The aim of this project was to support an air conditioning system and heating equipment to maintain a good indoor environment. Proportional integral differential (PID) control using cadmium sulfide (CdS) sensors was applied to control it. Polaroid film was attached to the new blind system to reflect sunlight. It was found that the system had the potential to reduce energy consumption and may be used with a building energy management system (BEMS).