Bhagavad Gita, Chapter 15, Verse 12

The light which, residing in the sun illumines the whole world, that which is in the moon and in the fire, know that light to be Mine.

Even the sun's real brightness is named here as borrowed light, not its own original source.

Sun, moon, and fire are all traced back to the same real origin rather than treated as independent phenomena. Real light, wherever it's found, is shown sharing one root.