Answer 1:
Excellent question.
All light is some kind of wave, including visible
light. Visible light is in fact only a very small
part of what is known as the electromagnetic
spectrum. The word "light" is more of a
conversational term.
The electromagnetic spectrum is called so
because the phenomena of electric and magnetic
fields are very closely tied to each other, and
are collectively described with what is known as
Maxwell's equations.
The length scales on the electromagnetic
spectrum range from wavelengths as large as sports
fields (radio waves) to as small as atoms
(x-rays). And yes, those are the same waves as
what you would listen to on the radio of your car
or what you get at the doctor's office to look at
your bones. You can see the vast range
here
As you can see, the visible spectrum only takes up
a small portion of the expanse covered by the
electromagnetic spectrum.
The reason we call it visible light is because
it is light that is visible to the human eye.
Otherwise, it is simply electromagnetic
radiation of a particular wavelength.
To understand how color works, we need to look
a little closer into how the human eye is
constructed, see basic anatomy of the eye
here
In the retina, there are cells known as
photoreceptors that are responsible for our
vision. Two types of photoreceptors exist- rods
and cones. Rods are for vision are low light
and don't contribute to color perception. Cones on
the other hand are active a high light levels and
contribute to color perception. These
photoreceptors are color sensitive to three types
of colors- blue(ish), green(ish), and
red(ish). I add an "ish" because there is a
distribution of wavelengths to which these
photoreceptors are sensitive . Our
perception of color happens when light strikes
these photoreceptors and interact with the
pigments inside.
It turns out lots of animals have cones that are
receptive to wavelengths of light outside what we
consider "visible light." Read more about it
here . My favorite is the mantis shrimp. The
Oatmeal (a webcomic) does a far better job at
portraying the awesomeness that is the mantis
shrimp, so
I will let it speak for itself .
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