Bhashya
कार्यकरणव्यतिरिक्तं कार्यकरणसंघातानुग्राहकं च ज्योतिः तत् बाह्यैश्चक्षुरादिकरणैरुपलभ्यमानं दृष्टम्; न तु तथा तत् चक्षुरादिभिरुपलभ्यते, आदित्यादिज्योतिःषु उपरतेषु; कार्यं तु ज्योतिषो दृश्यते यस्मात्, तस्मात् आत्मनैवायं ज्योतिषा आस्ते पल्ययते कर्म कुरुते विपल्येतीति; तस्मात् नूनम् अन्तःस्थं ज्योतिरित्यवगम्यते ।किंच आदित्यादिज्योतिर्वि-लक्षणं तत् अभौतिकं च; स एव हेतुः यत् चक्षुराद्य-ग्राह्यत्वम्, आदित्यादिवत् ॥
In plain words
This light -- the one standing apart from the body and its organs, yet quietly holding that whole assembly together -- we've already watched it come through the eye and the other senses, out in the ordinary world. But this inner light doesn't work that way. Even when every outer light, sun and all, has gone dark, the eye never catches it. And yet you can see what it does: because of the self alone, as his own light, a person sits, moves, works, comes back. So it's certain -- this light lives within. And there's more: it isn't like the sun's light at all, and it isn't made of matter either. The very reason we know this is that no sense organ can lay hold of it, just as the sun itself escapes every sense but one.
Close to the Sanskrit
That light which is distinct from the effect and instrument, and which assists the aggregate of effect and instrument, has been observed to be perceived through the external organs such as the eye. But that light is not perceived in that way, through the eye and the rest, when the lights of the sun and so on have ceased. Yet its effect is seen; therefore, by the self alone, as his light, this person sits, goes about, does work, returns. Therefore it is surely understood that the light is situated within. Moreover, it is distinguished from the light of the sun and so on, and it is non-material as well; the very reason for this is that it cannot be grasped by the eye and the rest, as with the sun and so on.