- "Stannis Baratheon, Warrior of Light... your sword awaits you."
In the books
In the A Song of Ice and Fire novels, Lightbringer is a sword of legend, forged and wielded by Azor Ahai, chosen by the Lord of Light to fight the darkness. He wielded the blade during the Battle for the Dawn, where he led the Night's Watch and the Children of the Forest and defeated the Others and ended The Long Night. The sword was said to glow and radiate heat, burning whoever touches it.
Stannis' Lightbringer is not claimed to literally be the same sword. Just as the Prince That Was Promised is supposed to be reincarnated, Lightbringer is supposed to metaphorically "come again". The recreated sword wielded by Stannis does glow brightly, but it does not radiate heat.
- Lightbringer at A Wiki of Ice and Fire (MAJOR spoilers from the books)