When I was a young child, I used to love to apply pressure to my closed eyes with my fingers because it made a bunch of cool patterns appear. It turns out, the patterns of light you see when you rub your closed eyes hard are called phosphenes. Cool!

The picture above is an artist’s attempt to depict what phosphene’s look like.

From Wikipedia:

The most common phosphenes are pressure phosphenes, caused by rubbing the closed eyes. They have been known since antiquity, and described by the Greeks. The pressure mechanically stimulates the cells of the retina. Experiences include a darkening of the visual field that moves against the rubbing, a diffused colored patch that also moves against the rubbing, a scintillating and ever-changing and deforming light grid with occasional dark spots (like a crumpling fly-spotted flyscreen), and a sparse field of intense blue points of light. Pressure phosphenes can persist briefly after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen on the visual scene.

(If you liked this, you might like Travels in Japan.)