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It said to use red colur objects as a sign of danger because it is scattered at least and hence can be seen from far?

But if use suppose blue colour bulb in a open area (where no objects to absorb light) , I agree that its rays will not reach us when far because all colour is already scattered and hence we cannt see it.

But why we cannt see even that scattered blue light from far(very) , although we can see scattered light from sky that is much farther than blue bulb?

It is said that during time of sunset or sunrise, appears red as all blue colour is scattered very before, My doubt is why cannt we see that blue colour scattered light? Although it is said our eye can watch at infinity.

Just because scattered light is far, we cannt see it, Can't scattered light reach us from that far?

2 Answers2

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Suppose you placed a bulb very far away(say infinity). Now if the bulb is turned on, you can't see the light at infinity, because of the intensity, as you can see in this image, The farther the light travels the more area it has to cover, now a bulb shining at infinity have to cover an infinite area where you are standing(at infinity from bulb).
Thus the density of rays decreases very much, and become invisible.
Note- You can see a bulb shining when you are close to is because it's intensity and light ray density is high, but as you move away both decreases and at a point you can't see the bulb anymore.

The Space Guy
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Red things are used as stop signs because of our vision, not because red light travels farther. Red things appear bright to us because of the way our brain works. Not all that many things are red, so a red object is not likely to blend in to the background.

In clear air, scattering works over longer distances. At noon, light travels straight down through the atmosphere. The atmosphere gets thinner and fades away with altitude, but about half of it is below 3 miles high. At sunset, light travel a longer path through the atmosphere.

Blue light scatters more often and at a larger angle than red light.

At sunset, almost all the blue light from the sun has been scatter away from its original path. So when you look directly at the sun, red predominates.

Likewise, when you look near the sun, you are looking at an angle almost directly at the sun. A lot of what you see is red light that was almost aimed at you, and has been deflected a little. You will get some blue, but a lot of the blue was deflected at a sharper angle.

When you look at $90^o$ from the sun, you will see the sky is still blue, particularly if you look up. Light that was headed somewhat in your direction, but higher gets overhead before it is deep in the atmosphere. There is it scattered. Blue light is likely to be scattered $90^o$. Red light is not. So the sky appears blue.

mmesser314
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