as measured by Cinzano [@Cinzano2005] in comparison to the Johnson V filter response function defined by the Johns Hopkins University [@Dobos2004].[]{data-label="fig:sqmresponse"}](Figure1.eps){width="13cm"}

For the moment both SQM and Johnson V measurements seem to be suitable to quantify artificial NSB. But having in mind that light emitting diodes (LEDs) are developing fast, a change in the night sky brightness composition can be expected. Since future LEDs of color temperatures above 3000K may have a significant emittance in the blue part of the spectrum, Johnson V band measurements would not be able to register a change in color of the NSB. Since the SQM is sensitive to the blue end of the spectrum, it seems to be prepared for future measurements of the sky brightness in case of stronger contributions at the blue end of the spectrum. The best one can do without spectroscopy is attaching a set of SQMs parallel to each other, each equipped with a standard photometric filter (LRGB or UBVR). Such a configuration makes it possible to study the NSB development and to record possible changes in the color of the night sky at the same time (see Kyba et al. [@Kyba2012a]).

### Sampling rate

We started our measurements 