Katha Upanishad Verse 2.2.15

The Self is the source of all illumination in the universe; it is the light that survives when all other lights—the sun, moon, stars, and fire—fail. Every manifested light in the universe is but a reflection of this supreme, self-effulgent Light. Neither the sun, moon, stars, nor fire shine there; it is by Its light alone that everything else is made visible.

Sanskrit Verse

न तत्र सूर्यो भाति न चन्द्रतारकं नेमा विद्युतो भान्ति कुतोऽयमग्निः ।
तमेव भान्तमनुभाति सर्वं तस्य भासा सर्वमिदं विभाति ॥ १५ ॥

Transliteration

na tatra sūryo bhāti na candratārakaṃ nemā vidyuto bhānti kuto’yamagniḥ |
tameva bhāntamanubhāti sarvaṃ tasya bhāsā sarvamidaṃ vibhāti || 15 ||

Translation

The sun does not shine there; nor do the moon and the stars, nor do these lightnings shine. How could this fire? Him shining, all shine after. All this shines by his light.