Various studies are currently carried out to solve a problem of lighting energy savings, as the importance of it increases. Especially, a variety of researches and application of light-shelf are conducted, as their efficiency has been acknowledged. However, in order to enhance the daylighting performance efficiency of a light-shelf, using materials with high reflectivity becomes a problem due to glare. This study undertakes performance evaluation according to light-shelf's reflectivity on the summer solstice and aims to draw proper light-shelf variables based on the analysis results. The results of this study are presented below: 1) The increase of reflectivity and angle of a light - shelf raises average illuminance and illuminance deviation. 2) the increased angle and reflectivity of light-shelf improve the average of illumination, while uniformity factor varies. This suggests that we should be carefule to construct light-shelf. 3) The number of measured illuminances meeting standard illuminance, 400lx, is the same from 70% to 90% of the reflectivity of a light - shelf, which proves that simple enhancement of light-shelf's reflectivity is not favorable to daylighting performance improvement. 4) Proper variables of a light-shelf on the summer solstice are drawn to 10° in angle and 70% in reflectivity.