Explanation: light: face; Clan: Clan; Yao: Show off; Zu: Ancestor. Win glory for the clan and let the ancestors shine.
Source: The fourth fold of Yuan's Qujiang Pool: "It is a great honor to be a student today."
It is not an idiom to leave a name for posterity. It means to let the name appear in future generations, that is, to let future generations set an example.