A Sword Called Clarity

Clarity is a human-forged longsword, but close examination reveals it uses elven techniques to entwine two blades into one.  

This well-made long sword has the words FIAT LUX along one side of the entwined blade and the word VERITAS on the other.  These are the command words for two related, yet distinct powers.

Sword of Hearth and Home by Chris Rahn, Magic the Gathering

By uttering FIAT LUX, the sword becomes the center of a double-strength Daylight spell, extending out 120' in each direction, and moving with the swordbearer.

Speaking the word VERITAS causes the wielder's eyes to glow a solid blue.  These glowing eyes function as Truesight, True Seeing, Arcane Sight, detect alignments by the auras of varying colors around each being, and can see into the Ethereal and Astral planes; basically, the wielder gets Wizard Vision.  

Depending on what they see, however, can drive the viewer temporarily mad, stunning them into inaction as they see everything as it truly is.  Mechanically, this is a Wisdom save at DC 15 (or higher depending on what the DM knows is actually there).  Failure to save means the viewer is stunned for a round.  This save is made each round until it is made, then the glow in the eyes fades away, returning the eyes to normal, but the PC changed.

While stunned, the PC just stands there, defenseless.  Successful strikes against the stunned viewer allow an additional saving throw.  

This experience leaves the viewer far more knowledgeable, but with a level of exhaustion.  At the DM's discretion, there may be a small chance for a permanent increase (or loss) of Wisdom for the PC.