Weapon (longsword), Rare, Requires Attunement
This item appears to be a sword hilt.
Blade of Radiance. While grasping the hilt, you can take a bonus action to cause a blade of pure electric energy to spring into existence or make the blade disappear. While the blade exists, this magic weapon functions as a longsword with the Finesse property. If you are proficient with Longswords or Shortswords, you are proficient with the Air Blade.
You gain a +2 bonus to attack rolls and damage rolls made with this weapon, which deals Lightning damage instead of Slashing damage.
Electricity. The sword’s luminous blade emits bright light in a 15-foot radius and dim light for an additional 15 feet. The light is sunlight. While the blade persists, you can take a magic action to expand or reduce its radius of Bright Light and Dim Light by 5 feet each, to a maximum of 30 feet each or a minimum of 10 feet each.
Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.