In sensus plenior darkness is Love as expressed in unity, grace, mercy, long-suffering, patience, etc. and Light is Holiness, as expressed in separation, law, justice, judgement, patience etc.
The Trinity existed in darkness/love before creation, but the Light/holiness was hidden in God, as expressed in the pun for Elohim (alo khoom - meaning 'not dark'). The Light, or the revelation of God as Holiness did not exist because there was nothing for him to be separate from. As soon as there was a creation, holiness could be expressed.
Light, as a metaphor for holiness, was pre-existent, but hidden in God himself.
God's revelation of himself is given in two paths Holiness and Love. When we understand them individually, He reconciles them on the cross. What was parted at creation is joined at the cross.