Robert, you plan to go to the site where the IR illuminators are already? Why are you disconnecting 1/2 of them instead of none or all but one, etc.?
Sorry I am not sure what you are trying to do.
Btw, for those interested in measuring IR, see: How to Measure IR Illumination
We include maintenance on our systems. Some of the systems are permanent sites, others are temporary (on construction sites). For the temporary sites the equipment comes back and we refurbish the equipment before they are redeployed, including replacing all the IR illuminators. For the permanent sites we are planning on replacing them after 3 years or if we think the illumination is down. We are now compiling a stack of these units and would like to evaluate them before throwing them into the garbage. My thinking is that it is not practical to test them in the field.
your question about disconnecting 1/2 of them:
What I meant to say is that to calibrate the test apparatus I would take a new illuminator of a particular wattage and beam angle and obtain a reading, then re-test it with 1/2 the LED lamps in the unit disconnected so I get two data points. I would then compare that with the unit removed from the field (of same wattage and beam angle) and test it in the same apparatus.