1)
Why does it say that it is darkness, and not light?
1.
Radak: There is not even a little light. It is totally darkness. Darkness is a Mashal for affliction.
2.
Malbim: Why do you look forward to Yom Hashem? It is darkness, and not light. There is no hope for salvation!
2)
Why does it add "v'Afel v'Lo Nogah Lo"?
1.
Malbim: Ofel is worse than Choshech. In Choshech there is some Nogah (radiance) from the moon and stars. In Ofel, there is no Nogah at all.
