It is the effulgence of all luminaries. It is said to be beyond darkness (ignorance). It is Knowledge, the One to be known and reached by Knowledge alone. It is established in everyone’s heart.
Krishna is explaining the Kshetrajna, describing it as the supreme source of light, the revelatory power. For all the brilliant entities, it is the one source, which is beyond darkness.
Brilliance is not just the external light, distinct to the eyes. Like external sensory objects, we have internal, invisible ones too, like thought, emotion, enquiry, knowledge and memory. In fact, all products of mind and intelligence are also subtle objects revealed by the same ‘I’.
Wakefulness results in sensory luminosity. But, who reveals what is brought in by the senses? In dream, in the absence of sensory signals who reveals the dream world? The real source of both outer and inner ‘light’ thus transcends light and darkness.
In fact, all dualities and multiplicities prevail only because of this transcendental singular presence.