How does zodiacal light affect the SQM readings?
It is likely to be less than a 1 or 2 percent effect. The primary reason is that the brightest and widest part of the zodiacal light is nearest the horizon where the SQM has almost no sensitivity (due to it being a zenith-looking device). The portions at higher altitude are the narrowest and faintest and they would barely creep into the sensitivity cone of the SQM.
