The Vedanta Sutras of Badarayana, Commentary by Sankara (SBE38), tr. by George Thibaut  at sacred-texts.com
3. (The light into which the soul enters is) the Self; owing to the subject-matter of the chapter.
But how can the soul be called 'released,' considering that the clause 'having entered into the highest light' speaks of it as within the sphere of what is a mere effect? For the word 'light,' according to general usage, denotes physical light. And none who has not passed beyond the sphere of what is effected can be released, it being known that whatever is an effect is tainted with evil.--This objection is without force, we reply; because in the passage referred to the word 'light' denotes the Self, in accordance with the subject-matter of the chapter. For as such the highest Self is introduced in the words, 'The Self which is free from sin, old age, death,' &c., and we therefore may not all at once pass over to physical light; incurring thereby the fault of abandoning the topic under discussion and introducing a new one. Besides, the word 'light' sometimes denotes the Self, as e.g. in the passage, 'That the gods meditate on as the light of lights' (Bri. Up. IV, 4, 16). We have discussed this at length under I, 3, 40.