While you're at it . . . whatever you have for overhead lights, split them between two switches. It's much easier on the eyes to go from darkness to half light than darkness to full light.
I always have one in my pocket. I use it almost every day at work anyway, and to see my way to my car (I leave home most of an hour before dawn, even in high summer, and hours before sunrise in the winter). However, do please remember to leave your cell outside the darkroom when changing film. If it rings, it'll fog everything that's out...