In Psalm 18:28 David says, “For You light my lamp; the LORD my God illumines my darkness.” That God would “illumine (his) darkness” could mean something different than we might initially think.
We might assume that when David says “You illuminate my darkness” that it means that God reaches down and changes the difficulties of his situation, so that where it was a sorry state, and he had some great problems, now he does not — OR, on the other hand, it could mean that even in what really is still a dark situation, there is yet “light” in it for him, because GOD is with him! Thus the presence of God becomes for him “light” and comfort in what is otherwise a very real darkness.
This would correspond with what we know of real life situations, and of the promises of God’s word. The Lord never promises His children that we will not experience dark hours here on earth. But He does promise to never desert us or forsake us (Hebrews 13:5). And His presence makes all the difference in our dark days: “Yea though I walk through the valley of the shadow of death, You are with me …” (Psalm 23:4) “Because He is at my right hand, I will not be shaken.” (Psalm 16:8)
If you know that the presence of God is with you, then even in your darkest times you can say with David here: “The Lord my God illumines my darkness.”