Click the control or press E to activate.
The Secondary Spike Intensity control, part of the Secondary Effects group, sets the intensity of the Secondary Spikes, which are additional faint and fuzzy pseudo-random spikes that accompany the main spikes. To some extent these Secondary Spikes can seem to be a glow, especially very near a star.
Higher Secondary Spike Intensity values yield stronger Secondary Spikes.
Note that because of the large number of Secondary Spikes, they can make the star seem larger and more colorful.