In this paper, we suggest to use a sky radiance model which accounts for heterogeneous distribution of light fixtures, their photometry, the ground reflectance and topography, to infer the point to point contribution of Canary Islands to the artificial sky radiance at Observatorio del Teide (Tenerife) and Observatorio Roque de los Muchachos (La Palma). In-situ hyperspectral sky radiance measurements, acquired on site in 2010, have been used to calibrate the model and to evaluate its inherent error. We aim to identify and characterize zones at which any lighting level increase or decrease may have a larger impact on light pollution at both European Northern Observatory sites, and then help to control and/or reduce their light pollution levels. This innovative methodology, can then be seen as a high level decision tool to help local authorities to restrict or reduce light pollution with the objective of protecting research class astronomical sites.