How is symbolism used for when the author uses the sunlight and shade when Ralph is hiding?A citation would help a ton too.
This is basic light and dark imagery/symbolism. What is hidden in the dark is what you don't want others to know about you--the dark side of human nature. Evil lurks in dark places. However, what is in the light is easily seen--there for all to witness. This is why most people act completely differently in public than at home.
Ralph is a good kid, but he is hiding in the shadows away from the evil that is manifested in Jack and the kids who are hunting him. In this case, the evil is in the light and the good is hiding in the dark. Ralph is also at a point where he is beginning to understand the evil of human nature as Simon and Piggy did when he is running for his life. The "truth"="light" is about to dawn on him, but he never quite gets there while on the island.
The "light" of the fire also saves Ralph from the evil of the boys and the island.