Ahh, I see. It looks like allyally must have originally intended to make it part of the gameplay to push the red button to turn on the lights but then opted not to in the end.
It's an arrow with a node dropping on it! That's obvious, Mo! The arrow disappears if you let the node drop, but if you delete the node, the arrow will stay moving back and forth. It's really useless, except that it makes the moonlights come out.