He saw the sea of waves, long dark waves rising and falling under the moonless night. A tiny light twinkled at the pierhead where the ship was entering: and he saw a multitude of people gathered by the waters’ edge to see the ship that was enter the harbour.
James Joyce, A Portrait of the Artist as a Young Man (New York: Oxford University Press, 2008), pg. 22
The darkness he sees is representative of the darkness he sees in his mind from time to time and that he feels within himself. He often relies on others to help him find the truth, as the ship relies on the light to help it find the harbor.