IR Night Time Illumination - Testing Methodology

I tried to search articles on this topic but could not find any. One issue that we run into sometimes is customer expectations of a stated IR night time range (e.g. 60ft IR range). There is no standard for this. I am wondering if there is a testing methodology that we can adopt based on what perhaps IPVM uses today or on something subscribers have found to be useful. We can certainly continue what we have been doing so far which is getting a visible image on the face and ensuring IR is even accross the FOV in an outdoor and indoor (warehouse) setting (with and without background). However being able to adopt a standard that our customers can understand and perhaps replicate to see identical results would be desirable.