Changes in night sky brightness after a countywide LED retrofit

The US National Park Service (NPS) Night Skies Program measured changes in sky brightness resulting from a countywide lighting retrofit project. The retrofit took place in Chelan County, a gateway community to North Cascades National Park and Lake Chelan National Recreation Area in Washington State. The county retrofitted all 3,693 county-owned high pressure sodium (HPS) street lamps to full cutoff LEDs. This number is about 60% of the County's...