Lancelot
Adventurer
The original D&D lightsaber was the wand of force, first introduced in the classic module WG4 - Forgotten Temple of Tharizdun. The wand of force had two modes; use a charge to create an effect similar to otiluke's resilient sphere (trap a creature in a force bubble), and a secondary effect where you could spend a charge and a blade of blue-white light sprang forth from one end of the wand, which could then be wielding as a magical blade. Hard to get any more "on the nose" than that.
In 3e, the equivalent was the various radiant energy weapons. Unlike 4e and 5e (where radiant was simply a damage type, like necrotic or fire), the radiant energy blades specifically ignored armor bonuses to AC. In other words, they targeted the creature's Touch AC. This was also consistent with lightsabers - able to cut through virtually any substance, except for a few special materials like cortosis.
The 5e sunblade, by contrast, just seems to be a glowing magical sword to me. That's a pretty common fantasy trope. The lord of the fire giants from Norse myth, Surt (or Surtr), had a sword that glowed like the sun. Elvish blades glowed near orcs in Tolkein's works. I've read plenty of pulp fantasy where the hero has a magical blade that glows with a blinding light while the hero is in the thick of battle, or fighting an enemy that the sword was specifically designed to defeat. In any case, I certainly don't think the comparison is quite as obvious as the wand of force or radiant energy weapons.
Having said that, of course, if you want the sunblade to be a lightsaber, then a lightsaber it is! For optimal use, make sure the PC with the lightsaber is a Fighter / Monk / Sorcerer with the witchbolt spell prepared. "Now you will feel the power of the Dark Side, young Skywalker..."
In 3e, the equivalent was the various radiant energy weapons. Unlike 4e and 5e (where radiant was simply a damage type, like necrotic or fire), the radiant energy blades specifically ignored armor bonuses to AC. In other words, they targeted the creature's Touch AC. This was also consistent with lightsabers - able to cut through virtually any substance, except for a few special materials like cortosis.
The 5e sunblade, by contrast, just seems to be a glowing magical sword to me. That's a pretty common fantasy trope. The lord of the fire giants from Norse myth, Surt (or Surtr), had a sword that glowed like the sun. Elvish blades glowed near orcs in Tolkein's works. I've read plenty of pulp fantasy where the hero has a magical blade that glows with a blinding light while the hero is in the thick of battle, or fighting an enemy that the sword was specifically designed to defeat. In any case, I certainly don't think the comparison is quite as obvious as the wand of force or radiant energy weapons.
Having said that, of course, if you want the sunblade to be a lightsaber, then a lightsaber it is! For optimal use, make sure the PC with the lightsaber is a Fighter / Monk / Sorcerer with the witchbolt spell prepared. "Now you will feel the power of the Dark Side, young Skywalker..."
