Does passing through a colored medium cause light to become that color or to lose that color? Why is the atmosphere different?

Question

It's well known the effect of Rayleigh scattering on the color of the sun, and it's explained several times on this website. Here's one of them. The summary of these explanations is, that when light travels through a colored medium, that color is being "used up" to make the medium the color it is, and only the other colors will go through.

Make very much sense. But the problem is that our experience in everyday life is just the opposite. When we shine a light through a colored medium, the light becomes the same color as the medium. Although it's hard for me to understand why (this was asked here without an impressive answer). And that's also happening with sunlight that goes through colored glass.

So why does the atmosphere behave different than anything else? And is there anything I can experiment with that would have the same behavior as the atmosphere?

Answer 1

There are two mechanisms that lead to extinction of light:

• Scattering,
• Absorption.

Most everyday materials like e.g. colored glasses or transparent colored plastics absorb light, which means that they take some frequencies away, and reflect+transmit the remaining ones, which means that the color you see them have is also the color they turn light into when looked through.

But in the atmosphere, namely the troposphere, the dominant extinction mechanism is scattering, which indeed leads to the scattered light being blue while the transmitted part is orange. In the stratosphere, in addition to Rayleigh scattering by (mostly) nitrogen and oxygen molecules, there's an ozone layer, which makes the light bluer by absorption. This makes the twilight blue instead of sandy-colored that it would have without ozone.

Aside from atmosphere, you can see such scattering extinction in some other materials via the Tyndall effect. E.g. opalescent glass can exhibit this (image from the article linked):

Another example of such behavior is in coated glass, where the coating uses interference of light to enhance transmission of some frequencies or to reflect them efficiently. In particular, you might have noticed that typical medical eyeglasses reflect purplish light when turned into one orientation, and greenish when in another.

Answer 2

You're confusing 2 different things.

1. Atmospheric scattering, Rayleigh scattering. In this process, the molecules of air act as dipoles and as such they respond to light and reradiate the light. But when they reradiate the light it has a strong wavelength dependence that scales as the the inverse of Wavelength^4. Since blue light is ~400 nm, and red is ~800 nm in wavelength, blue light will be much more strongly scattered. While the longer wavelengths (eg. red) will be less scattered. The scattering occurs at 90 degrees relative to the incident light. If you look at a sunset it appears more red. This is because the blue is scattered away at 90 degrees.

2. Absorption in a material. Here, there are molecular states, or electric states that will absorb certain colors of light, and in some cases will couple the energy gained by the atoms or molecules to the lattice as heat. So the light is lost. So if I have 2 colors of lights (W1, and W2) and the material absorbs W1, then only W2 will emerge. W1 is lost to heat.

Answer 3

I think you got it the wrong way round. The light that is seen through a colored glass is the specific wavelength which is not scattered.

The medium doesn't need to "use up" (absorb) the light to be that color, rather letting the light through and scattering every other wavelength. Maybe it is unintuitive, because one could think of color as a possession. It would then make sense for an object to absorb a certain wavelength to "posses" a color, but that's not true.