Share '2 piece base century'

Hi there, I’m just wondering if anyone knows why the 2 part base centuries do not cast much light out of the pin holes? Seems like the ‘70’s ones really have quite the display of light emitting from the holes on the base.  Also wondering if anyone knows where to find a new black bottom for the base? The previous owner apparently took it off or it broke or something.  Would I have to just buy a b…