Bhashya
न्स्वात्मभूते ब्रह्मणि सर्वावभासकोऽपि सूर्यो भाति, तद्ब्रह्म न प्रकाशयतीत्यर्थः ।स हि तस्यैव भासा सर्वमन्यदनात्मजात प्रकाशयति, न तु तस्य स्वतः प्रकाशनसामर्थ्यम् ।तथा न चन्द्रतारकम्, न इमा विद्युतो भान्ति, कुतोऽयमग्नि अस्मद्गोचरः ।किं बहुना ।यदिदं जगद्भाति, तत्तमेव परमेश्वरं स्वतः भारूपत्वात् भान्तं दीप्यमानम् अनुभाति अनुदीव्यते ।यथा जलमुल्मुकादि वा अग्निसंयोगादग्निं दहन्तमनुदहति, न स्वतः , तद्वत्तस्यैव भासा दीप्त्या सर्वमिदं सूर्यादि जगद्विभाति ।यत एव तदेव ब्रह्म भाति च विभाति च कार्यगतेन विविधेन भासा, अतस्तस्य ब्रह्मणो भारूपत्वं स्वतोऽवगम्यते ।न हि स्वतःऽविद्यमानं भासनमन्यस्य कर्तुं शक्नोति ।घटादीनामन्यावभासकत्वादर्शनात् भारूपाणां चादित्यादीनां तद्दर्शनात् ॥
In plain words
Even though the sun illuminates everything else, it does not illuminate Brahman; rather, the sun shines only by the light of Brahman, possessing no independent power of its own. Neither the moon, the stars, nor flashes of lightning shine independently—how then could this fire? Whatever shines in this universe does so only in reflection of that Supreme Lord who is inherently light. Just as a heated ember burns by the borrowed power of fire and not on its own, so too does this entire universe shine through the sheer radiance of Brahman. Because Brahman alone shines in various forms through its effects, its intrinsic nature as pure light is self-established. An unluminous object cannot illuminate another, just as a pot cannot; illumination belongs solely to things whose very nature is light.
Close to the Sanskrit
Even though the sun is the illuminator of all, it shines not in the Self-existent Brahman; that is the meaning. For it illuminates all other non-self objects by the light of Brahman alone, and has no independent capacity to shine of itself. Similarly neither moon nor stars nor these lightnings shine; how then this fire here? What need of more? Whatever this universe shines, it shines after that very Supreme Lord who shines by nature as light, being luminous. Just as water or an ember heated by fire burns following fire, not by itself, similarly by the light and brilliance of Him alone all this sun-and-other universe shines forth. Since that Brahman alone shines and shines diversely through manifold modal light, therefore the luminous nature of that Brahman is understood by itself. For that which does not exist inherently by itself cannot make another shine, as pots and others are not seen to illuminate others, whereas luminous entities like adityas are seen to do so.