Wisp are representing dancing flux of energy that are usually invisible.
Like an aura, the particles flies around living species, especially plants and trees. The wisps are evolving, almost dancing around the trees in nice curves, like a ballet of lights.
The glow they cast will play nicely with the volumes of the tree, revealing the branches as the light flows.
They reveal the magic of nature, saying it still exists, even in the most common places of the urban space.