I can mainly add this to the discussion
https://web.science.mq.edu.au/~ross/...tex-notags.pdf
There method seemed to be to take a mosaic of the night sky with a fairly low focal length length, e.g. DSLR and compare the brightness against known star brightness, allowing a way to loosely calibrate brightness values off the stars,
I would expect this to allow you to find your sky glow spots, then you might be able to use a diy spectrometer e.g.
https://publiclab.org/notes/homechem...n-spectrometer to narrow down how effective each filter might be,
Edit: i should add my site based on the website is 18,000ucd. However i have been investigating a kind of dark site that reports about 380ucs not too far a drive away. But I expect it to have some pretty horrible sky glow to the north and west