Although seemingly unchanging, today, our ability to see stars on a dark night is in danger of disappearing. The reason for this is the widespread growth of light pollution from inadequate lighting systems. This study, which used a range of methods, presents the results of light pollution measurements taken within the Mont-Mégantic International Dark Sky Reserve (MMIDSR), which was created in 2007 to protect the quality of astronomical observations and research at the Mont-Mégantic Observatory, and to preserve the exceptional starry nightscape visible from the site. Two essential elements of artificial night lighting were considered: its source and its diffusion in the atmosphere. Analyses showed that despite a global trend towards an increase in light levels, population growth on the outskirts of the Parc national du Mont-Mégantic, and the arrival of problematic types of lighting fixtures on the market, the level of light pollution in the MMIDSR has remained stable over the last 10 years, not only at the zenith but across the entire sky.