How to create a "Center Rim Light" effect?

Question

I've been looking into replicating shaders used in some Unity games for a while, and while I have found a solution for almost all the issues I ran into there is still one issue that stumps me.

Certain objects use a shader with an effect that is referred to as "Center Rim Lighting" and essentially functions as a glowing specular of sorts. The shader has a locked range of 0.5 to 50. At 0.5, the glow takes up almost the entire object, while at 50 it becomes extremely small and weak, but does not disappear entirely.

I have been able to create a "fake" rim light effect for the edges of my models, but trying to invert the same method does not work at all. (I would post an image if my attempt even remotely resembled the screenshots from Unity, but what I tried literally looks nothing alike)

Every other component of my shader recreations all use Principled BSDF and Mix/Add Shaders to achieve what I've done so far, so I would prefer the solution to still use those shaders if possible. If it does require a different shader type though, then I guess I can still work with it as long as I can mix it with my preexisting setups well.

Answer 1

The best I can get is something like this - Use the From Min, To Min, and To Max on the Map Range node to control the density and spread of the purple specular reflection. The ColorRamp is there for even tighter control (optional):

EDIT - try this - I swapped the glossy node for an emission, and mixed it with a transparent to lessen its affect. I also added a node chain to allow you to control the "rim" amount by using the values between 0-20 on the Value node on the left side. Also, setting the To Min manually closer to 1 makes the dot smaller/disappear and vice versa, if you want to start from a smaller or larger "center point":

Also, I just re-read your comment, I suppose to better suit your needs, it would make more sense to change the From Min and From Max on the first Map Range Node (after the Value node) to 50 and .5, respectively (instead of 20 and 0 - the positions are reversed compared to normal, so the purple grows as the number increases). After this, any value between .5 and 50 on the value node will influence the size of the purple "dot" (or "center Rim Power", as it's called).