Useful Indicators
When you look out the window of your plane, you’ll notice that the spheres are getting closer together as you approach the end of the runway. The distance between those markers is usually only 30 to 50 feet. As a result, they serve as useful indicators that the craft is approaching the tarmac’s edge.

Useful Indicators
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Fire-Colored Spheres
Nevertheless, why are the visibility markers red? They’re well-placed because they can be seen against the sky! However, according to a later FAA study, orange is a more visible color for pilots. So, even if there are still exceptions, you’re more likely to see fire-colored spheres hanging from power lines these days.

Fire Colored Spheres