In Inkscape if you have two filled circles. A big solid red one and a smaller, blurred and pinkyÂ one, like this:
You can use the mask to trap one inside another to create a light effect.
Metaphorically, I drew a mask using the mask effect:
You can download it here: mask_inkscape_by_silveiraneto.svg
As always, you can use or modify it under the Creative Commons Attribution Share-Alike license.