Blinding Smite
The target hit by the strike takes an extra 3d8 Radiant damage from the attack, and the target has the Blinded condition until the spell ends. At the end of each of its turns, the Blinded target makes a Constitution saving throw, ending the spell on itself on a success.
Using a Higher-Level Spell Slot. The extra damage increases by 1d8 for each spell slot level above 3.
Blinding Smite 5.5e 2024 vs. 5e 2014 edition differences
The 2024 version applies the Blinded condition until the spell ends, whereas the 2014 version only blinds the target until it succeeds on a Constitution save. The 2024 version explicitly states the target makes the save at the end of each turn, and the damage increases by 1d8 per spell slot level above 3.