JMNT(i)
12 Jesus therefore again spoke to them [i.e., to those whom He had just been teaching, in vs. 2, or at a later time],
saying, "I Myself am (or: continuously exist being)
the Light of the world (or: of the cosmos; of the ordered system; of the dominant cultural, political, economic and religious arrangements; of the universe; of ‘the theater of history’ – Walter Wink).
The one habitually and progressively following Me can by no means walk around (= under no circumstances live his or her life)
within the darkness (or: the dim and shaded areas; the gloom and obscurity due to the lack of the Light of the Day; the [realm] of the shadows; [note: = ignorance; = that situation which existed before the Light came; or, could also refer to the dim condition within the holy place of the Temple, or to the darkness of death, blindness or the womb]),
but, to the contrary, he will progressively possess (constantly have and hold)
the Light of 'the Life!' (or: the light which is life.)
"