||We proceeded to the modelling of the night sky brightness of Montsec area (north-east of Spain), an astronomical protected area certified as a Starlight Reserve. We have used the hyperspectral version of ILLUMINA, an artificial sky brightness model. Ground based measurements for Montsec and other areas of Catalonia 0015 ; 0016, including both photometric and spectroscopic data, has been used to fit and evaluate the input parameters of the model. In this first modelling attempt, Lleida, the biggest city in the area, has been considered as the unique source of light pollution. In 2014 there was an update of the lighting infrastructure in Lleida. A detailed comparison of the sky brightness before and after the change is shown in order to measure the effects that different kind of lamps can produce. This information could be used to plan for future updates and improvements of the lighting systems in the area.