Light emitted near and above the horizontal scatters into the atmosphere creating what is known as sky glow. Some light aimed downward is so intense that it reflects back up and also adds to sky glow. This light travels miles in our atmosphere effecting areas far from the origin of the light.
Big Bend National Park in southwest Texas is known for it’s dark skies. This is especially true since the 2010 lighting upgrade. Now the light pollution you can see from Big Ben National Park is from El Paso, 300 miles away!
Each of our choices of light fixtures and the amount of light those fixtures produce determine how much sky glow will be created each night. Think about that. This is the easiest pollution to eliminate. We create it anew every night.
With our current choices in lighting, about 80% of the U.S. population has never seen the Milky Way. You can help change that.