For realizing the ZEB (net zero energy building), thorough saving energy of the illumination is necessary. Although task ambient lighting is expected as a key technique of energy saving illumination in office, it is not widely shredded because of the low brightness impression. We established a luminous environment control method that can improve an impression of the indoor brightness using a brightness index. The control system is constituted from ”a luminance measurement”, ”brightness evaluation” and ”illumination control”. In this paper, the appropriate range of the brightness index clarified by a subject experiment, calculation logic of dimmer ratio to maintain the appropriate brightness with minimum electricity consumption and results of the operation performance applied in actual work place are reported.
