Sure... I deleted my last post as I cross-posted with bb.

Here is the ISF shader. Save it somewhere in your Materials library folder and remove the .txt file extension.

The shader has four parameters. When you have positioned a light, its position must be copied into the XYZ parameters in the shader. This is so it can calculate the distance from the light source to the point on the surface currently being rendered, and hence the intensity at that point.

The other parameter specifies the distance from the light at which the actual light intensity will be equal to the light's dialled intensity. I usually leave the intensity dial at 100% and use this parameter to adjust intensity - I find this method more intuitive, but you can do it either way.

If you use Parmatic, it will create dials for these four parameters on the light's Parameters palette.

"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)