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  • What if you could only see one color?

  • Imagine, for instance,

  • that you could only see things that were red

  • and that everything else

  • was completely invisible to you.

  • As it turns out,

  • that's how you live your life all the time

  • because your eyes can only see

  • a minuscule part of the full spectrum of light.

  • Different kinds of light are all around you everyday

  • but are invisible to the human eye,

  • from the radio waves that carry your favorite songs,

  • to the x-rays doctors use to see inside of you,

  • to the microwaves that heat up your food.

  • In order to understand

  • how these can all be light,

  • we'll need to know a thing or two

  • about what light is.

  • Light is electromagnetic radiation

  • that acts like both a wave and a particle.

  • Light waves are kind of like waves on the ocean.

  • There are big waves and small waves,

  • waves that crash on the shore

  • one right after the other,

  • and waves that only roll in every so often.

  • The size of a wave is called its wavelength,

  • and how often it comes by

  • is called its frequency.

  • Imagine being a boat in that ocean,

  • bobbing up and down as the waves go by.

  • If the waves that day have long wavelengths,

  • they'll make you bob only so often,

  • or at a low frequency.

  • If the waves, instead, have short wavelengths,

  • they'll be close together,

  • and you'll bob up and down much more often,

  • at a high frequency.

  • Different kinds of light are all waves,

  • they just have different wavelengths and frequencies.

  • If you know the wavelength or frequency

  • of a wave of light,

  • you can also figure out its energy.

  • Long wavelengths have low energies,

  • while short wavelengths have high energies.

  • It's easy to remember

  • if you think about being in that boat.

  • If you were out sailing on a day

  • with short, choppy waves,

  • you'd probably be pretty high energy yourself,

  • running around to keep things from falling over.

  • But on a long wavelength sea,

  • you'd be rolling along, relaxed,

  • low energy.

  • The energy of light tells us

  • how it will interact with matter,

  • for example, the cells of our eyes.

  • When we see, it's because the energy of light

  • stimulates a receptor in our eye

  • called the retina.

  • Our retina are only sensitive to light

  • with a very small range in energy,

  • and so we call that range of light visible light.

  • Inside our retina are special receptors

  • called rods and cones.

  • The rods measure brightness,

  • so we know how much light there is.

  • The cones are in charge of what color of light we see

  • because different cones are sensitive

  • to different energies of light.

  • Some cones are more excited by light

  • that is long wavelength and low energy,

  • and other cones are more excited

  • by short wavelength, high-energy light.

  • When light hits our eye,

  • the relative amount of energy each cone measures

  • signals our brain to perceive colors.

  • The rainbow we perceive

  • is actually visible light in order of its energy.

  • At one side of the rainbow

  • is low-energy light we see as red,

  • and at the other side is high-energy light

  • we see as blue.

  • If light shines on us

  • that has an energy our retina can't measure,

  • we won't be able to see it.

  • Light that is too short wavelength or high energy

  • gets absorbed by the eye's surface

  • before it can even get to the retina,

  • and light that is too long wavelength

  • doesn't have enough energy

  • to stimulate our retina at all.

  • The only thing that makes one kind of light

  • different from another is its wavelength.

  • Radio waves have long wavelengths,

  • while x-rays have short wavelengths.

  • And visible light, the kind you can actually see,

  • is somewhere in between.

  • Even though our eyes can't detect light

  • outside of the visible range,

  • we can build special detectors

  • that are stimulated

  • by these other wavelengths of light,

  • kind of like digital eyes.

  • With these devices,

  • we can measure the light that is there,

  • even though we can't see it ourselves.

  • So, take a step back and think about

  • all of this for a moment.

  • Even though they seem different,

  • the warmth you feel from a crackling fire

  • is the same as the sun shining on you

  • on a beautiful day,

  • the same as ultraviolet light

  • you put on sunscreen to protect yourself from,

  • the same thing as your TV,

  • your radio,

  • and your microwave.

  • Now, those examples are all things here on Earth,

  • things you experience in your everyday life,

  • but here's something even more amazing.

  • Our universe gives off the full spectrum of light, too.

  • When you think of the night sky,

  • you probably think of being able

  • to see the stars shining with your own eyes,

  • but that's just visible light,

  • which you now know is only a tiny part

  • of the full spectrum.

  • If we had to draw the universe

  • and could only use visible light,

  • it would be like having only one crayon --

  • pretty sad.

  • To see the universe in its full spectrum,

  • we need to have the right eyes,

  • and that means using special telescopes

  • that can help us see beyond visible light.

  • You've probably heard of the Hubble Space Telescope

  • and seen its beautiful pictures

  • taken in visible and ultraviolet light.

  • But you might not know

  • that there are 20 space telescopes in orbit,

  • missions that can each see part

  • of the full spectrum of light.

  • With telescopes acting as our virtual eyes,

  • both in space and here on Earth,

  • we can see some amazing things.

  • And the coolest thing of all,

  • no matter the wavelength or energy,

  • the light that we see out in the distant universe

  • is the same thing as the light

  • that we can experience and study here on Earth.

  • So, since we know the physics

  • of how x-ray,

  • ultraviolet light,

  • or microwaves work here,

  • we can study the light of a distant star or galaxy

  • and know what kinds of things

  • are happening there too.

  • So, as you go about your daily life,

  • think beyond what your eyes can and can't see.

  • Knowing just a little bit about the natural world

  • can help you perceive the full spectrum

  • around you all the time.

What if you could only see one color?

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B1 TED-Ed wavelength energy visible visible light retina

【TED-Ed】Light waves, visible and invisible - Lucianne Walkowicz

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    稲葉白兎 posted on 2015/01/17
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