This study sought to determine how irradiance at various distances affected the hardness of a new silorane-based composite compared to a methacrylate-based composite resin restorative material. A visible-light curing unit was used at low and high irradiances. Plastic molds of various thicknesses (1, 2, 3, and 4 mm) were filled with composite resin and polymerized for 20 seconds at various distances (0, 2, 4, and 6 mm). After 24 hours of storage at 37°C, the microhardness of each specimen was tested at the bottom surface using a microhardness tester. These microhardness values were expressed as a percentage of maximum microhardness and analyzed with ANOVA and Tukey's post-hoc tests. At both low and high irradiances, the silorane-based composite (shade A2) was capable of acceptable (80%) bottom-to-maximum microhardness ratios at increments up to 3 mm and at curing distances up to 4 mm (at low irradiance) and 6 mm (at high irradiance).