This is to be understood either of the light of the sun, and the rays of it, which are so piercing and penetrating as to reach to the bottom of the sea, and cover it and exhale waters out of it; or of lightning, which is equally as piercing and penetrating, or more, and strikes to the very roots of the sea, and covers them, or rather discovers them, so that the channels of waters are seen, and the foundations of the world are discovered, Ps 18:14; the Targum of this verse is,"he spreads upon it rain, and covers the rocks or foundations of the sea;''and the rain is called light according to Ramban, because by the descent of it the day is enlightened, and the darkness of the clouds removed; and by this means the bottom of the sea is covered, so that it passes its bounds and covers the rocks, that is, the borders of it, as others explain it .
Myh yvrv "radices maris", Pagninus, Montanus, &c.