Jamieson, Fausset and Brown on Job 10:22

22. The ideas of order and light, disorder and darkness, harmonize (Ge 1:2). Three Hebrew words are used for darkness; in Job 10:21 (1) the common word "darkness"; here (2) "a land of gloom" (from a Hebrew root, "to cover up"); (3) as "thick darkness" or blackness (from a root, expressing sunset). "Where the light thereof is like blackness." Its only sunshine is thick darkness. A bold figure of poetry. Job in a better frame has brighter thoughts of the unseen world. But his views at best wanted the definite clearness of the Christian's. Compare with his words here Re 21:23; 22:5; 2Ti 1:10.