Could you give an example of such a pic that caught your eye?
Some programs such as Xenodream produce '3D' fractals, and luminosity is part of the 'lighting' setup available. Other programs such as UltraFractal are 2d, and any 'luminosity' is due to either the coloring scheme chosen, or to post-production work in another program.
Also, if a particular piece catches your interest, write an IM to the artist of that piece. Most of us welcome questions and comments on our techniques, and are willing to share information freely.

RosemaryR
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"This...this is magnificent!"
"Oh, yeah. Ooooo. Aaaaah. That's how it starts.
Then, later, there's ...running. And....screaming."