Bará, SalvadorTapia Ayuga, Carlos EugenioZamorano Calvo, Jaime2023-06-172023-06-172019-03-171424-822010.3390/s19061336https://hdl.handle.net/20.500.14352/13359© 2019 by the authors. This work was partially supported by Xunta de Galicia/FEDER, grant ED431B 2017/64 (SB), and partly developed within the framework of the Spanish Network for Light Pollution Studies, REECL (AYA2015-71542-REDT). CET and JZ acknowledge funding by the Spanish MICINN AYA2016-75808-R, by the Madrid Regional Government through the TEC2SPACE-CM Project (P2018/NMT-4291), and by STARS4ALL, a project funded by the European Union H2020-ICT-2015-688135.We develop a general optical model and describe the absolute radiometric calibration of the readings provided by two widely-used night sky brightness sensors based on irradiance-to-frequency conversion. The calibration involves the precise determination of the overall spectral sensitivity of the devices and also the constant G relating the output frequency of the light-to-frequency converter chip to the actual band-weighted and field-of-view averaged spectral radiance incident on the detector (brightness). From these parameters, we show how to define a rigorous astronomical absolute photometric system in which the sensor measurements can be reported in units of magnitudes per square arcsecond with precise physical meaning.engAtribución 3.0 Españajournal articlehttp://dx.doi.org/10.3390/s19061336https://www.mdpi.comopen access52Light-pollutionFísica atmosférica2501 Ciencias de la Atmósfera