We have chosen the lensed version because we also use the devices in urban regions where the field of view is limited due to surrounding buildings. A wide beam width then could result in lower accuracy due to the possible influence of nearby lights.

An advantage of the ethernet version is that with network cables far greater distances can be reached than with USB cables and by making use of the “Power over Ethernet” (PoE) technology also power supply at remote sites is easier to handle. Furthermore, the PoE device directly attached to the SQM leads to a sufficient amount of heating as to avoid the formation of dew.

### Spectral response function of the SQM and comparison to the Johnson V band

Sky Quality Meters are equipped with a photo diode, a filter and a temperature sensor for thermal stabilization. The manufacturer provides information on the sensitivity curve of the photo diode and the filter, but not the resulting response function. Previous reports indicated that the night sky brightness values measured by SQMs do not differ strongly from those from systems equipped with a Johnson V filter. Nevertheless, given that SQM magnitudes are not the same as V magnitudes, 