न तत्र सूर्यो भाति

This verse found in the Katha Upanishad (2.2.15) and Mundaka Upanishad (2.2.10) articulates the nature of Brahman as self-luminous pure consciousness. The core meaning is that the Ultimate Reality (Brahman) is the source of all light (consciousness) in the universe. The verse uses examples of luminous objects like the sun, moon, stars, lightning and fire, to point out that even though we consider them as sources of light, they are themselves illuminated by a higher principle. It suggests that consciousness itself is what makes all perception and knowing possible, including luminous objects and light itself.