Measuring the Light
Scientists measure all different kinds of pollution, including air pollution, water pollution, soil contamination, and plastic pollution. But how do they measure light pollution? When outdoor light fixtures emit light, the light gets scattered into multiple different directions. Some of this light escapes directly into space, some gets reflected off of the atmosphere to create skyglow, and some gets reflected off of the ground and up into space. Two ways that light pollution data can be collected is through satellite imaging and ground-based studies that can be done by anyone.
Satellite Imaging
Similar to how satellites are able to track changes in the size of polar ice caps and holes in the ozone layer, satellites can also track changes in where artificial lighting is being used around the world. Since the 1970s, scientists have been using data collected from weather satellites to learn more about how much artificial light escapes into space. This image below from the National Institutes of Health shows how the use of artificial lighting in the United States grew between the 1950s and 1997 with a prediction of how much there will be in 2025. As populations increased and artificial lighting technology became better and cheaper, the number of outdoor artificial lights and overall light pollution also increased.
Ground-Based Studies
From using instruments to participating citizen science projects, there are a few ways that light pollution can be measured from the ground. Instruments like Sky Quality Meters help measure the brightness of skyglow in any part of the world. Another tool that can be used to measure night sky brightness is the naked eye. As skyglow gets brighter, stars get dimmer. So, stars you would be able to see in a dark sky would not be visible when there is a lot of skyglow.
As a way to help estimate how dark the night sky is using stars, constellations, and the milky way, John E. Bortle created the Bortle Dark-Sky Scale. This scale has nine levels with one being the darkest sky and nine being the brightest. This image below from Cloudy Nights, an online community of amateur astronomers, shows the difference in how many stars the naked eye would be able to see between each level. These tools can be used by anyone to measure the brightness of the sky and help scientists better understand light pollution in different places around the world.
How Much Light Pollution is There Where you Live?
Find out about light pollution in your own backyard using these sources below!
Light Pollution Interactive Map of the World: https://www.lightpollutionmap.info/
This color-coded map shows how much light pollution there is around the world. Scroll around the map and click on different places to see how they compare to where you live.
Globe at night Citizen Science Project: https://www.globeatnight.org/webapp/ OR the free Loss of the Night smart phone app (for iPhones and Androids)
These citizen science projects can be done without any extra equipment. Just using the naked eye, you can help record the light pollution in your own backyard.
Sources:
https://www.darksky.org/light-pollution/measuring-light-pollution/
https://www.lrc.rpi.edu/programs/nlpip/lightinganswers/lightpollution/skyGlowMeasured.asp
http://www.bigskyastroclub.org/lp_bortle.html
By Amanda Leith
