Sun Blade
Weapon (longsword), rare, requires attunement · 2014 rules, SRD 5.1
Blade of radiance: +2 attack and damage, deals radiant damage, +1d8 radiant vs undead, finesse; bright light 15 ft adjustable; proficiency with shortswords/longswords applies.
Also in the 2024 rules (SRD 5.2).