Hi,
Treez - you produce mains connected electronics (for lighting).
Thus you should have a high voltage isolation meter, like Metriso.
With it you should be able to measure your floor resistance.
There will be standards where you can read how to do this.
Without knowing these standards...
I assume a some kind of meaningful method could be:
Use a 10cm x 10cm metal plate, with conductive foam between metal plate and floor, put a full bottle of water on it, and measure the resistance against protecting earth (water pipe, heating pipe) with the isolation meter.
I assume (hopefully) there is construction steel (mesh) inside the concrete, it should easily spread the ESD energy over a huge area.
At least it should form a relatively large capacitor.
Klaus