How does Mary Shelley, in Frankenstein, use images of light and dark to make the creature more frightening?
The use of light and dark imagery in Mary Shelley's Frankenstein is quite different than the typical use of light and dark imagery (typically it is used to contrast or name as something good or evil). In Shelley's novel, light and dark imagery tends to speak to the absence of light, focusing more on the presence of darkness.
In regards to the creature, the absence of light insures the creature is always placed in the middle of darkness. When readers first come in contact with the reader, the creature is so pained by light that he must close his eyes.
By degrees, I remember, a stronger light pressed upon my nerves, so that I was obliged to shut my eyes.
On a side note, after closing his eyes, the creature is frightened by the darkness. In essence, this shows that the monster is not meant to exist--given he has no place in the light or the dark.
Outside of the use of darkness to cloak his existence, as seen all chapters where the creature is able to tell his story, the creature is never really "brought into the light" for the reader. His true physical appearance is never detailed. Readers must create a mental image of what they believe the creature to look like. What this means is that Shelley, in a beautiful omission, excludes light from ever shining upon the creature. Instead, her cloaking of the creature, placing him in darkness, proves to be frightening. Readers never really know what they, or the character in the novel, are facing. Given they never "see" the creature, fears can never be faced and the creature's ability to frighten the reader compounds.