Currently, if your eyes are closed you can still get a sense of the light around you, and moving your head around you can tell if you’re moving it toward or away from a light source (barring maybe if you’re outdoors and it’s bright out all around you).
But what if when we closed our eyes it was like full blackout? Would blinking become disorienting? Could it mess up circadian rhythms? Something else? Or would it not really matter?
There was a study of a guy who lived underground for months with no timekeeping devices. His only contact was with other researchers by telephone, and not often. His sleep schedule and length he’d stay awake got super wonky but he had no idea. So the complete lack of light certainly has an effect.