It is only a partial solution and works better for spots than point lamps.
With volume you can see what it is doing,
basically it gets rid of the light in the part of the ray that is less than twice the radius size. If you set the “less than” to less than twice the radius you will start getting a halo.
Both the point and spot have a radius of 1m.
in this one I lowered the less than value to 1.8.
I know it is more a “dirty hack” than a solution.
Most of the rays from the light path do not work because lights do not have a diffuse, glossy or transparent component. Objects cast shadows, lights cast light… well negative lights cast shadow but I do lot think the light path node considers them “shadows”.
The rays do have length and depth so those outputs can be used.
Ray depth is the number of bounces and ray length is the length of the ray.
Here I excluded the first 2 bounces of the light, so there is no direct or first bounce but there is a third fourth etc.
Here I used a gradient to change the colour of the light rays depending on their length factor.
