Each year an intercomparison of the light meters is being performed. All light meters then monitor the night sky at one and the same location and the results are being compared.

In the graph at the right an intercomparison of the light meter of Arnhem in 2014. Vertical the results of the lightmeter of Arnhem and horizontal the average of five other light meters. All data are on one line as they should.
Frequency diagram
In the graph to the right all the measuring results of 2014 for the light meter at Cabauw are being presented. The vertical axis shows the number of measurements. The horizontal axis shows the night sky brightness, to the left it is darker and to the right it is brighter. De night sky brightness with first quarter moon and full moon is indicated.

There are two clear values which are more often present: the far most peak are the results for clear nights and the peak at the right shows the results for cloudy skies. This pattern is more or less visible at all measuring stations.
Evening / night rithym
To the right all measurements of a whole year 2014 in one graph. At the vertical axis the night sky brightness and at the horizontal axis the local time. Th ecolour in th egraoh shows how freqeunt a measurement occurs (red - the most, blue the least). The middle black line shows the average of the results. As can be seen that during the evening till midnight it slowly becomes dark in Cabauw and after 04:00 it becomes rapidly brighter. This pattern we see at all locations.
Darkness in the Netherlands online
NachtMeetnet is a tradename under Sotto le Stelle (Registered Utrecht Nr. 30167055)