Knowing that there is a problem is not enough. We need to know how much of a problem we have, is light pollution getting worse or is it getting better.
The more sky glow we see - the fewer stars we can see - but it can change over time. For better or for worse.
New technology lighting and fittings can reduce or increase light pollution of the night. More energy efficient lighting may even lead to more lighting.
There are several ways to monitor night sky quality.
Direct observation e.g. count the stars and compare with star charts with the sky.
The Globe at Night program is an international citizen-science campaign to raise public awareness of the impact of light pollution by inviting citizen-scientists to measure their night sky brightness and submit their observations to a website from a computer or smart phone. It's easy to get involved.
Android Loss of the Night App. The Loss of the Night app turns your eyes into a light meter, allowing you to become a citizen scientist and report how bright the night sky is where you live!
The Bortle Scale is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution. The scale ranges from Class 1, the darkest skies available on Earth, through Class 9, inner-city skies. It gives several criteria for each level beyond naked-eye limiting magnitude (NELM).
Use equipment to measure the sky brightness:
The Sky Quality Meter (SQM). The Canadian company Unihedron manufacture a range of well priced meters for measuring the quality of the night sky. These range from hand held units for individual readings to a range of computer of internet connected models which take and record continuous readings of the night sky. See Light Pollution Map below.
IPhone. A new app for the iPhone called Dark Sky Meter uses the phone’s camera to accurately measure the brightness of the night sky and deliver the results to a central database that will, in time, create a worldwide map of light pollution.
The International Year of Astronomy (IYA) Lightmeter,
Defence Meterological Satellite Program - The NGDC Earth Observation Group (EOG) specializes in nighttime observations of lights and combustion sources worldwide. The group started working with DMSP data in 1994 and has produced a time series of annual cloud-free composites of DMSP nighttime lights.
Light Pollution Map:- The light pollution map has two base layers (road and hybrid Bing maps), light pollution radiance overlays and the user light pollution measurements overlay.The light pollution 2010 overlay was made from "Version 4 DMSP-OLS Stable Lights Coverage".The light pollution 2014, 2015, 2016, 2017 overlays were made from "VIIRS DNB Cloud Free Composites".Data from 2010 and 2014/2015/2016/2017 is not comparable (different satellite systems)!!! Annual VIIRS comparisons are also to be avoided as there are too many factors involved by just doing a direct comparison. To add your SQM measurements turn on the "User SQM" overlay in "SQM overlay & filter" menu and click on the pencil icon in the toolbar. "SQM overlay & filter" menu also contains filters to limit the display of SQM measurements.