Why can you see a campfire from miles away but it only illuminates such a small area?

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asked Sep 9, 2020 in Camping/RV by one2 (260 points)
Why can you see a campfire from miles away but it only illuminates such a small area?

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answered Sep 9, 2020 by Jaybird (12,310 points)

The reason you can see a campfire from miles away but it only illuminates such a small area is because of reflection.

The light that illuminates the small area in the dark is reflecting it's light back through the atmosphere and those light particles bounce off different parts of the earths sky.

So you can then see the campfire from miles away because you're seeing the reflection of the fire bouncing it's light off different parts of the earth.

Also our eyes adapt to the way we see between high intensity light ( like that near the fire) and low intensity light (like that at night, hundreds of yards away from the fire).

We use our pupils to control the amount of light getting into our eyes at higher light levels.

The brighter the light, the smaller our pupils close to keep some of it out , and our eyes are detecting most of that bright light using a specialized light sensing cell - called “cone cells” - that are really good at detecting color. But cone cells need a lot of light. If they don't get it, they don't work.

When you walk away from the fire into the dark, the first thing your eyes do is open up your pupils to bring in more light, which works for a while.

Eventually, even this can't bring in enough light for the cone cells to work, but by the time your pupils are as wide as they can go, your eyes are shifting gears to use rod cells to detect light.

Rod cells can't make out color as well as cone cells, but need only a fraction of the light.

Your eyes work in this mode in the dark.

Your eyes work one way in bright light, and a different way in dim light.

You don't need to be a mile away from your campfire to see this.

On a clear night, sitting close to the fire, just look up and try to see the stars.

The fire light isn't going to reach your eyes if you're looking away from it, and you'll be able to sense when your eyes shift from high light to low light.

You'll go from seeing almost nothing to rather suddenly seeing stars. It's just your eyes changing from one mode to another.

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