I'm not sure where I put BB's original shader, but here is my modified version, freshly saved as an umcompressed (mt5) material file from an old scene I did in Poser Pro. You need to change the file extension from .txt to .mt5 and save it somewhere in your library materials folder.

I've arranged the parameters down the left side... x, y, z position of the light (in inches!). Ignore the existing numbers in those nodes, they are just where the light was in my scene. Above the position parameters is the distance setting (the distance from the light source at which the intensity is equal to that set in the light's base node). You can adjust both the distance and the base intensity as required.

I also added a cheat parameter at the bottom, to adjust the fall-off up or down from true inverse square. You can just leave that at 100 percent.

It should work fine, but do ask if you run into any problems with it...

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)