There are a couple important symbols in Mary Shelley's Frankenstein.
Light is a symbol which represents knowledge. For the two main characters in the text, Victor and the creature, knowledge is of the utmost importance. Both desire to shed light upon their lives. Victor's search for Forbidden Knowledge will shed light on the scientific community regarding death and reanimation. As for the creature, his desire for knowledge revolves around his need to find his identity. At the same time, light tends to hurt the eyes of the creature (in the same way his knowledge of his birth hurts him).
The symbol of fire is important for the creature. When cold, fire is able to warm a person. When the creature first discovers fire, he places his hand within the flame and is burned. This is ironic, given he needs to fire to stay warm. At the same time, this symbol mirrors the symbol of light: what the creature desires harms him.