Light is a wave-like phenomenon that consists
of alternating electric and magnetic fields. The
speed at which light travels is a constant, but
the wavelength - the distance over which the
alternating electromagnetic fields make one full
cycle - varies from one color of light to another.
The electric portion of light can alter the
positions of molecules (called 'rhodopsins') in
our eyes, which enable us to see it. Different
kinds of rhodopsins require more energetic,
shorter wavelength (more blue) light to affect,
which is how we distinguish different colors.
There is no limit to how powerful or how weak
light can be, however. Light that is too energetic
(ultraviolet and up) will simply destroy the
rhodopsins, while light that is not energetic
enough (infrared and down) are just not strong
enough to affect any of our rhodopsins, and as a
result, we can't see them.
We can, of
course, build machines that can detect colors of
light that we can't, and many colors of light we
can detect in ways other than vision. All colors
of light still carry energy, so if you are having
sufficiently bright light shining on you, you will
feel it as heat, even if it's of a color you can't
see. To prove it, you can try the following: hold
your arm out in the sun, and note how warm it
feels. Now hold your arm in the shade, and note
that it is cooler. Last, place your arm so that it
is in the sun, but behind a window. Your arm will
feel in-between the full sun and the full shade.
This is because the glass is stopping the infrared
and ultraviolet light, so your arm is only being
hit by a fraction of the sun's light.
can also build an antenna that will collect light
of a color with a wavelength equal to the length
of the antenna. That's how radios work.
When scientists, and especially physicists,
talk about light, they're referring to any
wavelength of radiation. There are certain
wavelengths of radiation that we can see (visible
light) but there are other wavelengths that we
cannot see. Some ranges of those radiation
wavelengths that you may have heard of before
include ultraviolet and microwave radiation. You
probably know that ultraviolet radiation can
cause sunburn, even though you cannot see it. You
probably also know that microwaves can cook food,
even though you cannot see that light either. If
you want to look at radiation in a little more
depth, here's a neat website I found: click_here
Our eyes are only able to see certain colors of
light. Mostly, we have evolved to see the light
that is emitted from the sun. This is the visible
light range which is around 400-700 nm. Light out
side this range would be invisible to us. Some
animals such as snakes can see light that we
can't, like near infra red light, or infrared
light from 800-1100 nm. This allows them to see
even in the dark, when there is no visible light.
Night vision goggles use this same idea, allowing
us to see NIR light.
Light occurs in a wide range of wavelengths.
We only see in a very small section of the entire
wavelength (visible light). Invisible light is
only the wavelengths that are outside the ability
of our eyes to see. On either side of visible
light is infrared light and ultraviolet light.
Photography can, using special film, capture these
lights in ways that we can see.Other animals, such
as some insects see in ultraviolet light. Certain
flowers have ultraviolet markers in them to guide
insects to where the pollen is.
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