When light hits your eyes, receptors in your eyes send a signal to your brain. Receptors that receive light also send signals to neighboring receptors that tell them to turn down, or inhibit, their sensitivity to light.
When you look at the white wall without a tube, you see a uniform field of brightness because all the receptors are equally inhibited. When you look through the tube that you made from a full sheet of paper, the spot of light is surrounded by the dark ring of the tube. The spot appears brighter because the receptors in the center of your retina are not inhibited by signals from the surrounding dark ring.
In contrast, light shines through the walls of the tube that you made from the thin strip of paper. When you look through this thin-walled tube, the spot appears darker because light comes through the wall of the tube, causing the receptors at the center of your retina to be inhibited. This is known as lateral inhibition.