For me a luminiscent perimeter is the first layer of the auras I see. Here in Minnesota, the fist layer of energy around the trees in Spring gets much wider as they return to life and that is very luminescent.
I don't know where you are at with your aura seeing practice, but as I worked with Brian Osborne's Aura Seeing course, which is what I assume you are doing (?) that layer expanded into much wider bands with different densities and colors.
All the best!