Find the point where light falloff reaches zero

Ok, so this problem has been bugging me for a day now. I have been trying to find a way in blueprints to get the point a lights falloff reaches zero. As the attached image shows I have a spherical trigger that I am using as a pain volume roughly at the lights edge, however I don’t want to use the attenuation as if the light intensity is low but the attenuation radius is high, then the player will still take damage if not lit.

Right now I am setting the pain volume by eye, but this means I would have to create an new light blueprint for each time I want a different lighting effect. What I really want is to find that light falloff radius, and then adjust my pain volume to match it. Does anyone know if that is even possible to do in blueprints via maths, or some variable I haven’t seen yet? Also I can’t see a whole lot of documentation on how intensity links in with distance?

If anyone had any ideas I would be greatly appreciative.