Pip’s childhood is overshadowed by the darkness of the marshlands. The first event of the book is him sitting in a cemetery when a convict comes up to him. Dickens describes the importance of the dreary marshlands for establishing the mood. 

My first most vivid and broad impression of the identity of things, seems to me to have been gained on a memorable raw afternoon towards evening. At such a time I found out for certain, that this bleak place overgrown with nettles was the churchyard. . . (Chapter 1) 

Light and dark can be metaphorical. For example, Miss Havisham keeps herself surrounded by darkness. She never leaves her house. Her isolation is a result of the difficult life she has led. The reason she remains hidden in the shadows is that she has lost faith in human nature and no longer wants to interact with people.

The darkness is both literal and metaphorical when Pip sees what is left of Miss Havisham's wedding cake.

Certain wintry branches of candles on the high chimneypiece faintly lighted the chamber; or, it would be more expressive to say, faintly troubled its darkness. It was spacious, and I dare say had once been handsome, but every discernible thing in it was covered with dust and mould, and dropping to pieces (Chapter 11).

The juxtaposition of light and dark is also represented in Estella's description of how she has no heart. She tells Pip he should stop pining for her, and compares the reaction boys have to beautiful women as moths drawn to a flame.

“Moths, and all sorts of ugly creatures,” replied Estella, with a glance towards him, “hover about a lighted candle. Can the candle help it?”

“No,” I returned: “but cannot the Estella help it?” (Chapter 38)

The absence of light throughout the story is not a coincidence. Darkness hides intentions and reality. Pip does not know what is really happening in his own life most of the time. He is metaphorically kept in the dark, and does not even know whose money he is using until Magwitch shows up (at night) to tell him. Magwtich is full of contradictions. Pip expects him to be frightening and a bad person, but Magwitch turns out to be generous and kind when the truth comes to light.