Background: The number of studies investigating the physical properties of light-curing units used in city centers in terms of the light intensity, presence of residues fractures at the tips, how long they have been used, and hardness measurements of the composite resins polymerized by these is limited. There is no such study in Turkey and Sivas province. The objective of this study is to examine the light-curing units used in Sivas city center and determine the reliability of light-curing units by measuring the surface hardness of composite samples polymerized with these devices. Materials and Methods: The power of the light-curing units that used in all private clinics in Sivas city center was measured. Then, the Vickers surface hardness measurements of the composite resin samples polymerized with these devices were made, and they were statistically evaluated. Results: The light intensity was found to be below from the acceptable value of 400 mW/cm(2) in 10.7% of the devices. It was observed that with increasing years of usage, the light intensity of light-curing units decreased (P < 0.05). Conclusion: It was observed that as the power of light-curing units increased, the hardness values of the bottom and top surfaces increased significantly.