I don't know if you have ever been in a place where there is LITERALLY NO light at all, but it is an absolutely unnerving feeling. There was cave tours near-by where I used to live and during the tour at the deepest part of the cave they would shut off the lights. That is some weird stuff. You go from looking at a cave full of people to seeing NOTHING, NOT A THING!!! You can't see your own hand in front of your face!!
Light is composed of packets of particles called photons, which interact with chemicals in your retina to create the image of what the light has most recently bounced off of. This is how your brain formulates its perception of reality.