Light vs. Darkness

Throughout Frankenstein, Mary Shelley uses light and darkness to describe Victor Frankenstein's mind frame.
"I had been calm during the day; but so soon as night obscurred the shapes of objects, a thousand fears arose in my mind. I was anxious and watchful, while my right hand grasped a pistol which was hidden in my bosom; every sound terrified me; but I resolved that I would sell my life dearly, and not shrink from the conflict until my own life, or that of my adversary was extinguished." ( pg. 144)
This shows that while it is light out, Victor's mind is cleared up of all confusion, but when it becomes night, there is a ton of fear and confusion. Everytime it becomes dark, the monster appears, and Victor faints or goes into some sort of fit, but when it is light out, Victor is fine, and the monster isn't in sight. Darkness makes Victor paranoid, and he turns into somewhat of a madman.