The Sword of Light of Nuada is one of the four treasures outlined in the Book of Leinster wherein is also described the origins of the people known as the Tuatha Dé Danann of ancient Ireland.
The original term, Claidheamh Soluis (Scottish Gaelic) is translated to “Sword of Light,” or “Shining Sword,” or a “White Glaive of Light,” that originates from Scottish-Gaelic folktales.
The sword is regarded as a god-slaying weapon from Irish mythology. It is said to have once belonged to Nuada Airgetlám, the first king of the Tuatha Dé Danann, whom named it Claímh Solais (phonetisized Klau-Solas), the sword of light. It was described as a fiery sword of glowing light, engraven with spells, and reputedly undefeatable once unsheathed.
It came from the mystical island of Findias, whose location was unknown but described generically as “in the north.”
It is a weapon that can either dissolve or deflect weaves of the one power depending on the need of its wielder. The only exception being that of balefire or its derivatives (such as the Flame of Tar Valon), a greenish twist of which was used by Balor, and the sword could not deflect it, killing Nuada.