We'll start with Bozeman, MT and an article by Katheryn Houghton of the Bozeman Chronicle (photo by Ryan Berry of the Chronicle) from Jan 2020: "Bozeman updated its light standards in 2017 to replace its streetlights with LED bulbs, which use less electricity and last longer than the high-pressure sodium bulbs the city previously relied on.... Some complained the new lights took over the night skies and seeped through their windows, an issue former commissioner Jeff Krauss repeated often in recent years on the board...[and] city staff have said they could dim and add shields to lights that are too bright."
The city owns and maintains 768 of the lights in town - the majority of which are LED -and the state has fewer than 70. Northwestern Energy owns the biggest chunk - 1,400 street lights - and a majority aren’t LED." Northwestern is now retrofitting with LEDs across the state. But ultimately there is a problem. Bozeman doesn't know who owns 1,100 of the 3,300 light fixtures in town.
Now we come to Keith Smith reporting in a recent 31 July article in AAAS Science: "Dimming or extinguishing street lights can reduce light pollution, but its efficacy has been difficult to measure. Barentine et al. [in Journal of Quantitative Spectroscopy and Radiative Transfer] monitored the sky brightness over the city of Tucson, [AZ], during a test of a new municipal street lighting system. The city authorities dimmed their streetlights at midnight, allowing the authors to determine that street lighting now contributes only 14% of Tucson's total light pollution. Further reductions must focus on other sources, such as private businesses and illuminated advertising."
Light polution is a serious issue being addressed by the International Dark Sky Association https://www.darksky.org/ The approach to reducing sky light pollution needs to focus on updating lighting codes and standards, but we need to convince our lawmakers there is a problem: Become a science-citizen to measure light pollution and advocate for a modern lighting ordinance in your town. There are many other things you can do - go to:https://www.darksky.org/get-involved/