SQM-L is not affected by horizon glow. Point the SQM-L it straight up.
See
http://unihedron.com/projects/darksk.../fovcurves.jpg for response chart.
Note there are other models with data logging.
I don’t have one and SQM-L has been on my wish list for years. You can get an app for your phone but I’m not sure how accurate it is.