John Chrysostom

But that you may learn that he speaks not of natural day and night, he calls the light, a great light, which is in other places called the true light; and he adds, the shadow of death, to explain what he means by darkness. The words arose, and shined, shew, that they found it not of their own seeking, but God Himself appeared to them, they did not first run to the light; for men were in the greatest miseries before Christ’s coming; they did not walk but sate in darkness; which was a sign that they hoped for deliverance; for as not knowing what way they should go, shut in by darkness they sate down, having now no power to stand. By darkness he means here, error and ungodliness.