The Sword of Light is known as Cliamh Solais in Irish (pronounced Klee-uv Shull-ish). This sword is one of the lost Four Treasures of Eirean. It was made in the northern city of Findias by a powerful fílí and magician named Uiscas.
According to the Lebor Gabála Erenn (the Book of Invasions), this Sword was brought to Éire by King Nuada of the Tuatha de Denann, he fought in a great battle (Cath Maige Tuired) against the Fir Bolg, who ruled Ireland at the time.
Nuada’s sword is seen as the embodiment of justice by dealing the ultimate punishment to Ireland’s enemies.