Purpose The purpose of this study was to investigate depth of cure of an opaque sealant when light cured from increasing tip distances with high irradiance light‐emitting diode (LED) curing units. Methods Ultraseal XT Plus opaque sealant was cured in a 2 × 2 × 5 mm covered slot mold using LEDs in high irradiance (VALO, SmartLite) or regular mode (Demi Ultra). Curing durations were 9, 15, and 20 seconds for the VALO, SmartLite, and Demi Ultra, respectively. The light tip was placed at three distances from the sealant surface (0, 3, and 5 mm; N = 10/group). Depth of cure was determined at the sealant surface and at 0.5 mm increments using Vicker's hardness (VHN). Results were statistically analyzed using two‐way ANOVA and multiple comparisons (α = 0.05). Results Depth of cure was significantly affected by the LEDs and light tip distance. At 0.5 mm below the surface, most combinations resulted in hardness higher than 80% of the surface value, except for SmartLite at 3 and 5 mm tip distances and VALO at 5 mm tip distance. Regardless of the tip distance, VALO and Demi Ultra achieved similar VHN values through 1.5 mm depth. Conclusions It is not likely that sealant is adequately cured with LEDs, even for those in high power mode, when the light tip is moved away from the surface due to lower radiant exposure.