What is the meaning of "Na'or Atah Adir"?
Rashi: This is like "Ni'er Mikdasho" (Eichah 2:7), "Ne'ertah 1 Bris Avdecha" (below, 89:40). He nullifies His enemies and those who rise against Him, and sweeps them from the world. He is called Na'or based on His deeds, like Chanun, Rachum and Kana.
Radak #1: This is like "Ni'er Mikdasho" (Eichah 2:7). The Nun is part of the root. Na'or is To'ar (descriptive); its grammatical form is like Gadol and Karov. He destroys enemies.
Radak #2: The root is Ohr; this is Nif'al conjugation, like Nachon. Na'or is like "Noda bi'Yehudah" (verse 2) - in that war He will be known and revealed like a clear light in Yisrael, and will fight their wars.
Malbim: Sancheriv's fall was at night. The verse depicts that Hashem left Har Tziyon to strike Machaneh Ashur like a lion leaves me'Hareri Taref to strike in a flock. He is called Na'or, for night is not dark for Him when He goes to strike the enemy camp.
Rashi explains those to mean nullifying. Others explain that they are destroying or distancing. (PF)
What is the meaning of "Adir me'Hareri Taref"?
Rashi: You are stronger than tearing giants who are tall like mountains. Compared to You, their Gevurah is not known.
Radak: You are mighty over the enemies like a lion that goes out from Hareri Taref, i.e. mountains on which lions, bears and tearing animals dwell, to tear. So You will tear all the enemies.
Malbim: You overpower and tear those who come to besiege Har Tziyon.
