First off, I tried repeating the nighttime infra-red photos (https://www.pmstudios.co.uk/blog/?p=7109) but using the filters to see what difference it made to the light – basically, not a lot! This implies that the infra-red lamps that I am using cover quite a wide spread of wavelengths. Here are the results:
The implication being that I don’t need to use filters with the infra-red lamps.
I also tried taking a street scene at night to see what that was like with the modified camera. Apart from the expected colour shift nothing seemed to be gained – this implies that there is little infra-red about at night: