Śivasaṃhitā 1.56

Two inseparable qualities of Spirit: light (prakāśa) and real existence (sat). What is known through something else is not a source of knowledge but an object of knowledge. Only Spirit, knowing itself and being the condition of possibility for all knowledge, deserves the name Light. And being the only reality, everything else only exists borrowed from It.

Svaprakāśa (self-luminous) is opposed to paraprakāśa (illuminated by another). The logical sequence is: no external illuminator → it is self-luminous → its nature is Light. Then: no other substance → it is One → without It everything is mithyā (false) → It is sat (real Existence). These chained reasonings (yasmāt… tasmāt) are characteristic of logical Vedānta.

The tradition identifies here three aspects of saccidānanda: Light corresponds to cit (Consciousness), Existence to sat (Being), and Bliss—which will appear in the next verse—to ānanda. The Śivasaṃhitā thus builds a complete phenomenology of the Absolute through a series of reasonings that move from experience toward transcendence.