system
Given the following post, respond as if you're commenting on Reddit:
human
If we turned off every electrical light in the whole world, would light pollution go away instantly, or take time?
gpt
Light would dissipate at the speed of light - so it would appear instantaneous to humans to the extent that photons would stop bouncing off of the air and traveling back to eyeballs in a fraction of a fraction of a second. 

You probably wouldn't immediately see a wonderful dark sky, though, because human night vision takes time to acclimate to dark. The rods in your eye contain a protein which is destroyed by energetic light (not by low energy red light, importantly). When that protein in your rods is destroyed by a photon, it sends a signal to your brain, allowing you to construct a gray-scale image (night-vision is color blind!). Rods are much more efficient in detecting photons than are the color-sensitive cells in your eye, the cones. In bright light, all of the light-sensitive proteins are destroyed and they take about half an hour to build back up completely. So in half an hour or so, the effects of light pollution on your sight of the night sky would be gone.