A Sky Quality Measurement of 20.92 is a very high value (and unfortunately exceptional).
The meteo conditions: a high pressure high over Western Europe, with mist. It was not a clear sky however, it was simply dark because of the dense mist. The blue graph indicate sthe sky temperature (IR measured), this needs to be way negative for a clear sky.
Also remarkable is the jump in SQM at the moments the public lighting switches off and on. The sky dims with a full unit of SQM. Despite the better LED fixtures, there is still a large impact of the public street lights.
