Background <p>The aim was to evaluate the effects of different curing times (3s/10s/20s) of an advanced Light-Emitting Diode (LED) curing unit on the degree of conversion (DC%), microhardness, and hardness ratio of three different composite resin materials.</p> Methods <p>180 cylindrical specimens (3 × 4&#xa0;mm; <i>n</i> = 60) were prepared from PowerFill (Ivoclar, Liechtenstein), PowerFlow (Ivoclar), and Omnichroma Flow Bulk (Tokuyama, Japan). Half of the samples were used for the degree of conversion analysis (nDC = 30), and the other half for the microhardness test (n VHN = 30). All specimens were irradiated using a Light-Emitting Diode (LED) curing unit (Bluephase PowerCure, Ivoclar). Based on polymerization times: 3-second rapid, 10-second conventional, and 20-second conventional; three sub-groups were formed for each material (<i>n</i> = 10). The specimens’ degree of conversion (DC%) was analyzed using Fourier Transform Infrared Spectroscopy (FTIR). Microhardness values were determined using the Vickers microhardness test, and the bottom-to-upper surface hardness ratios were calculated. The degree of conversion and microhardness were analyzed with a paired t-test, ANOVA, and Tukey tests (<i>p</i> &lt; 0.05).</p> Results <p>Comparisons among all groups revealed significant differences in upper and bottom DCs (<i>p</i> &lt; 0.05). PowerFill exhibited higher values on both surfaces after 3s polymerization, while PowerFlow required 10s and Omnichroma Flow Bulk 20s to achieve similar results (<i>p</i> &lt; 0.05). When the upper surface microhardness values were compared, no significant difference was found between PowerFlow and Omnichroma Flow Bulk in the 3s group (<i>p</i> = 0.623) and after 20s polymerization, between PowerFill and Omnichroma Flow Bulk (<i>p</i> = 0.082). Material type and polymerization duration significantly affected bottom surface microhardness values (<i>p</i> = 0.000). As the polymerization time increased, the bottom microhardness values of all materials increased. The highest microhardness ratio (HR) was obtained in the PowerFill group at 20&#xa0;s (<i>p</i> = 0.029). In the PowerFlow group, no difference was found between HR values of 10s and 20s (<i>p</i> = 0.238). For Omnichroma Flow Bulk group, all polymerization durations showed significant differences (<i>p</i> = 0.000).</p> Conclusion <p>The polymerization performed with an advanced LED curing unit in a shorter time (3s) resulted in varying polymerization efficiencies among different types of composite resins. For more homogeneous polymerization, it is advised to extend the duration to 10&#xa0;s or longer.</p>