The Self as Light
The Self is self-luminous, illuminating all experience.
The Self does not need another light to be known - it is self-luminous. By its light, sun, moon, stars, and all things are illumined. It is the light of all lights.
The sun does not shine there, nor the moon, nor the stars, nor lightning. How then this fire? Everything shines after Him. By His light all this is lit.
This reveals consciousness as the source of all knowing.
Katha Upanishad