tn The two nouns “cloud” and “darkness” form a nominal hendiadys: “and it was the cloud and the darkness” means “and it was the dark cloud.” Perhaps this is what the Egyptians saw, preventing them from observing Moses and the Israelites.
tc The LXX reads very differently at the end of this verse: “and there was darkness and blackness and the night passed.” B. S. Childs (Exodus [OTL], 218) summarizes three proposals: (1) One takes the MT as it stands and explains it along the lines of the Targum and Jewish exegesis, that there was one cloud that was dark to one group and light to the other. (2) Another tries to reconstruct a verb from the noun “darkness” or make some use of the Greek verb. (3) A third seeks a different meaning for the verb “lit,” “gave light” by comparative philology, but no consensus has been reached. Given that there is no easy solution apart from reconstructing the text, and given that the MT can be interpreted as it is, the present translation follows the MT.