Light pollution is an issue of global significance for urban ecosystems, especially where areas of natural and ecological importance are located in and around cities. We investigated levels of night sky brightness around Auckland, Aotearoa-New Zealand, to determine the extent of sky glow, its potential to mask the lunar cycle, its relation to land use and the risks it poses to nearby areas of natural and ecological importance. Annual measurements of night sky brightness were carried out over 3 years at 115 randomly chosen sites within 15 km of Auckland’s city centre. In addition, continuous nightly measurements of sky brightness were taken at 6 urban residential sites for 18 months. We found that levels of sky glow in urban Auckland mask the lunar cycle to some extent and modelling suggests that nearby marine and terrestrial areas of ecological importance are at risk. In 2015 and 2016, > 95% of the total expanse of these areas was predicted to be experiencing night skies brighter than natural levels. Increased night sky brightness was associated with proximity to the city centre, commercial and industrial land use, and densities of buildings and streetlights. Reducing sky glow in and around the city should be a management priority, directed at commercial and industrial land-use zones while restricting urban sprawl near areas of natural and ecological importance.