The rings are somewhat interesting, at first I was trying to figure out how it was even possible that there would be a "dark" ring around the center, seeing as the entire spillbeam is caused by light coming directly out the front of the window -- it shouldn't be possible for it to be there to be a "ring" dimmer than the sidespill.
I then realized that it actually wasn't any dimmer, but an optical illusion because of the contrast between the hotspot, the yellowish "halo" caused by the reflection off the aluminum ring, and the spill beam in between. If you point the hotspot of the light at something black so that it gets absorbed, and look at the "dark ring" you can see it's actually the same intensity as the spill off at the edges.
I think using the light in practice since you don't get the apparent contrast, the illusion isn't as apparent -- I think this is why so many have said that it doesn't show up as mcuh in real-world use.