The purpose of this study was to characterize the relation between total light energy and the final hardness of 4 composites polymerized under varying conditions. Four commercial composite restorative resins (Tetric Ceram(TM), Ivoclar Vivadent; Admira, Voco(TM); Arabesk (TM), Voco; Surefil(TM), Dentsply) were used to prepare 5 disk-shaped specimens (10 mm x 2 mm and 10 mm x 4mm) for each experimental condition. Photoactivation was carried out with a light device. The light-to-material distance was varied: (1) the light was maintained for 40 seconds with the end of the light source in contact (0 distance); or (2) the light was maintained for 40 seconds with the end of the light source is 10 mm away. Immediately after polymerization, Vickers hardness and surface roughness were determined on specimens surface that had been exposed to the light and on the opposing surface also. The specimens then were examined in the scanning electron microscopy (SEM) in different sections. The results were analyzed statistically. The Vickers hardness values of Surefil(TM), light applicated by 0 distance and 10 mm away, were significantly higher compared to other materials (p<0.001). The opposite surface of the surface exposed to light showed lower Vickers hardness values in all groups with the thickness of 2 mm and 4 mm.