🌌 Light Pollution Calculator
Curious how much artificial light might wash out the night sky where you are? Enter the population of the nearest large city and your distance from it for a rough sky-darkness estimate.
What Is Light Pollution?
Light pollution is excess artificial light that brightens the night sky, reducing the number of stars visible and affecting nocturnal wildlife. Astronomers commonly rate sky darkness using the Bortle scale, which runs from Class 1 (excellent, pristine dark sky) to Class 9 (inner-city sky, where only the Moon, planets, and a handful of the brightest stars are visible).
How This Estimate Works
Sky glow roughly follows an inverse-square relationship with distance from a light source and scales with the amount of light being produced, which is loosely tied to a city’s population. This calculator uses a simplified index, Light Index = Population ÷ Distance², and maps typical index ranges onto the approximate Bortle class they tend to correspond to in real-world sky-brightness surveys.
This is a simplified planning estimate, not a substitute for a measured sky-quality reading (such as with a Sky Quality Meter) or a light-pollution map. Actual sky brightness also depends on terrain, weather, moon phase, elevation, and the light-shielding practices used in nearby towns.