This study aims at revealing the spatial characteristics of traditional Japanese stroll gardens, through the interpretation of the luminous environment created by the architecture of tree canopies. Preceding studies on the garden spatial design have been typically done by means of observing the formal layout in the plan. Although this approach is successful for European formal gardens and modern landscape design, it could not be persuasive to reveal the special characteristics of Japanese traditional gardens, especially those with the organic layout of planting. Taking notice of the luminous environment under the tree canopies as the significant factor of the spatial characteristics, this study tries to establish the method to express it in the graphical representation. As the result, the study recognizes two luminous environment factors: the canopy brightness and the sunlight patterns through leaves. Observing these two factors, the following points are revealed: 1) four patterns of the canopy brightness and three patterns of the sunlight patterns through leaves are observed, 2) three types of plan organization, background, composite, and complex type, are observed, 3) two factors show different plan organization independently even in one garden, then those combination creates diversity of luminous environment, 4) the sequence of luminous environment along the path also shows particular pattern, and continuity and diversity of luminous sequence are not necessarily in the contradict relationship.