Thanks The Toss 
  
Yes, it does that. So looks like they are working, but I think the range / quality of these other cameras is nowhere near as good as my others.  
  
I think the IR range on them is very short, hence it seems like they aren't very effective.  
  
Oh well, they are fine daytime cameras, I will just move the better IR ones into the positions which are less well lit. 
  
Cheers