Jamieson, Fausset and Brown on Isaiah 5:30

30. sorrow, and the light is darkened--Otherwise, distress and light (that is, hope and fear) alternately succeed (as usually occurs in an unsettled state of things), and darkness arises in, &c. [Maurer].

heavens--literally, "clouds," that is, its sky is rather "clouds" than sky. Otherwise from a different Hebrew root, "in its destruction" or ruins. Horsley takes "sea ... look unto the land" as a new image taken from mariners in a coasting vessel (such as all ancient vessels were), looking for the nearest land, which the darkness of the storm conceals, so that darkness and distress alone may be said to be visible.