The anecdote relates how an inexplicable sacred light came from the temple's honzon when Emperor Shomu came to pray, and that he expressed his pleasure by changing the temple's name from 'Sugawara-ji' to 'Kiko-ji ('ki' means 'pleased', and 'ko' means 'light').
伝承によれば、聖武天皇が参詣した際に当寺の本尊より不思議な光明が放たれ、これを見た天皇が喜んで、「菅原寺」を改めて「喜光寺」としたという。