Darkness" is a state without light. "Light" is truth from the Lord, so "darkness" represents a state where truth is lacking. Here's a cogent passage from Arcana Coelestia: "The person who has yet to be regenerated is called 'a void and an empty earth', and also 'ground', in which no good or truth at all has been sown - 'void' where there is no good, and 'empty' where there is no truth. Consequently there is 'thick darkness', or stupidity and lack of knowledge about anything that has to do with faith in the Lord and so anything that has to do with spiritual and celestial life. (Arcana Coelestia 17)

478. The reason he is called Adam is that the Hebrew word Adam means man. But the fact that Adam was never used as a proper name, only Man, is quite clear from the consideration that both here and earlier he is spoken of in the plural and not in the singular, and that the term refers to both man and woman. The two together are called Man. Anyone may see from these words that both are included, for it is said, 'He called their name Man on the day in which they were created', and similarly in 1:26, 28, 'Let Us make man in Our image, and they will have dominion over the fish of the sea. This shows also that the subject is not about someone who, when created, was the first human being of all, but about the Most Ancient Church.