Since we hold cell phones so close to our faces, they can be even more stimulating than other devices. “Even though the amount of light coming out of [phones] isn’t huge, it’s all going right into our eyes,” Michael Grandner, Ph.D., the director of the Sleep and Health Research Program at the University of Arizona, previously told mindbodygreen. Not to mention, phones are tiny portals to distressing news, urgent emails, and other triggers that can raise our stress levels before bed.