Why does the red color travel the farthest in air but least in water. I mean we have danger signals red so that they can be spotted from farthest distance but in water as we go just 30ft down the blood turns green because red light couldn't reach even 30ft to bounce off the blood. Why is the behaviour of red color so opposite in two media?
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$\begingroup$ If I'm not mistaken, the reason for danger signals being red is that the human brain reacts specially to this colour rather than the light's energy being dissipated at a lower rate, also see this wikipedia article. $\endgroup$– sim0Commented Dec 17, 2021 at 15:45
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The wavelength dependence is different because the mechanisms are different. In air, the transmission of light is mainly limited by Rayleigh scattering. For this effect, the scattering strength is an inverse fourth power of wavelength, so blue light is scattered and lost from the transmission path, much more rapidly than red. There are other scattering effects too, from larger particles like dust
In water, the main effect is absorption of light, which arises from overtone and combination bands, based on fundamental modes which result from molecular vibrations (mainly -OH stretch) and occur in the infrared region. The intensity of these absorptions falls rapidly with the order of the overtone/combination so are weaker for blue light than for red. At much shorter wavelengths, other transitions come into play and the absorption increases again.
