In the lower left picture the tube is powered. The piece in the middle is dark but the surrounding thick ring is glowing green. The entire circle is not glowing brightly. At the bottom about a quarter of the circle is cut out. It looks like one of those cakes with a hole in the center. Someone has cut out about a quarter of the cake. Inside this dark area there is still a faint green glow. It looks like there is a source of green light in the center and some object has cast a shadow on the ring.
In the lower right picture the shadow area is just a small wedge. Someone with a very small apatite has cut a tiny piece of the cake. The shadow has almost closed up completely and almost all of the ring is bright green.
End of verbal description.