Right, but then you're ignoring ambient light. Your statement isn't true in a dark room, where the very much does care.
Screens should not be brighter than ambient light as a rule of thumb, i.e. if you hold a piece of paper next to your screen, the screen should not brighten up the paper. If it does, reduce brightness of your screen and/or turn up the light in your room.
So, a dark room is not an ideal working environment anyway.