" If circumstances require that your sleep habits depart from the earth’s natural light and dark cycles, make a strong effort to sleep with an eye mask (check mindfold.com for a total darkness sleep mask) in a completely darkened room, since all of your skin cells are sensitive and responsive to light—not just your eyes. "

― Mark Sisson , The Primal Blueprint: Reprogram Your Genes for Effortless Weight Loss, Vibrant Health, and Boundless Energy