Floor illuminance is an index that is generally used in lighting planning. Conventionally, when a space is designed based on this index, it has been difficult to take account of spatial brightness, a factor often considered important in the assessment of actual spaces. In this article, I report a case in which Feu1), an index proposed for estimating spatial brightness, is used in a lighting design so as to take spatial brightness into account. By implementing such a design, the designer has achieved energy saving while maintaining the same level of perceived brightness as the conventionally-designed spaces.