It might help to reorganize this question a little. I would break it up as follows:
How are images of light linked to the ideas of heaven and safe haven? Consider all kinds of light imagery in the text. There is light that comes from the sun, light that is present in open spaces (spaces not shaded by the jungle), light provided by the moon and stars, light caused by reflection, and light referenced in language (Simon's "candle buds" for example). Can you think of a lighted place that is also safe? Can you think of a "heavenly" character or place that is somehow lighted?
How are images of darkness connected to the idea of hell? How are the pig runs symbolic of hell? Consider darkness in the text just like you did light. Can you think of a dark or shaded place where"hellish" things happen? Can you think of a time when they boys do evil things in the dark? Why would the pig runs be connected to the idea of hell? Do bad things happen on the pig runs? Are they themselves dark? How is the Lord of the Flies, the ultimate symbol of evil, connected to the idea of darkness?