I have an impending low light photographic foray happening next month, to ensure things would be alright, I undertook some tests.
I will need to use my 65mm wide angle (4x5") lens, the light will be quite low, so reciprocity will come into it and evenness of the subject will be paramount. The subject is a light coloured building, with almost black exterior timbers showing, sort of a wedding dress and dark suit combination; if you know what I mean.
With that in mind I looked around to find something that would within reason, emulate the subject. I eventually ended up photographing my wood turning lathe, which is mostly black, with a light coloured wall in the background.
As the 65mm lens also has fall-off, I tested with my centre graduated filter attached to see just how even the negative received light across the frame; specifically across the top of the frame as the top of the building is also mostly whitish.
My film was Ilford FP4+, metered time was 2 seconds, corrected time was 2.39 seconds using Ilford's formula. Allowing for the fact I have difficulty in working out ½ second fractions; or what one would call a fudge factor, I decided 3 seconds was probably about right where the real exposure length would be.
All the pertinent information is in the file name.