Matt Soniak
Why Is Snow White?
by Matt Soniak - January 29, 2010 - 4:30 PM

Snow is just a bunch of ice crystals getting together, hanging out and having fun. So why is snow white when ice has no color?

iStock_000010776303-snowFirst things first, why are different things different colors in the first pla­ce? Visible light is made up of different wavelengths of light—from the shorter, violet ones to the longer, red ones. When light hits different objects, the different wavelengths have different reactions. Objects absorb a certain amount of light, and absorb certain wavelengths more than others. The wavelengths that aren’t absorbed as much (or at all) reflect off the object, and we perceive them as color. When you look at an object, the color you see is the combination of the light frequencies that the object did not absorb.

When light hits snow, it’s in for the ride of its life. All those ice crystals that make up snow are translucent, not clear, so the light doesn’t pass right through it, but bounces around back and forth off the different crystals. As the light bounces around, some of it is reflected, and some of it is absorbed. No one wavelength is preferentially reflected or absorbed, though, so all the different wavelengths—and therefore all the colors that we can perceive—are reflected to our eyes in equal measure. The color of a combination of all the frequencies in the visible spectrum in equal measure is white, so this is the color we perceive snow to be.

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Comments (16)

  1. My head hurts

    posted by Pattycakes on 1-29-2010 at 5:19 pm

  2. Oh crap….I actually get it.

    I guess that’s what dating a physicist who works in optics does for ya….

    posted by KerriD on 1-29-2010 at 5:40 pm

  3. My friend once raised the question if we all see colors the same. Sure we all know what blue looks like, but do we know it as blue because we were taught to identify it as blue even though what our eyes see may be different from person to person. I don’t know if that makes sense….

    posted by Shash on 1-29-2010 at 5:42 pm

  4. Shash, you bring up an interesting question. Suppose that at an early age you and your friend were told to look at the sky and then told that is blue. If you were looking straight up and your friend looking toward the horizon you would both see different shades of what you’d each call blue. So who is right? Well, each color and shade thereof have a unique frequency, thus to truly know what a color is, you would need to know its frequency. Of course, you could do as my son did may years ago when presented a helium balloon by his aunt. On being asked what color it was he replied gleefully “Periwinkle!” His aunt in a shocked voice said “Periwinkle! Perwinkle! No, it’s blue!” My son, crestfallen left the room, only to return a few moments later with 2 crayons. The darker one he held up to the balloon and said “BLUE! NO MATCH!” and handed it to his aunt with the label up. The second one he held up to the balloon and said “MATCH!” and showed his aunt the label which said periwinkle. This was his way of identifing the frequency of the balloon color. BTW, I believe that a polar bear’s hair folicoles are transperent like snow flakes and that’s why a polar bear is white.

    posted by Prism on 1-29-2010 at 6:50 pm

  5. When I was in Alaska I learned that glacial ice looks blue because all other wavelengths are absorbed by the ice, but the blue (the shortest wavelength) isn’t, so it’s reflected back at the eye and looks blue. I’ve also heard that the blue ice is actually colder than the white-looking ice.

    posted by Lynley on 1-29-2010 at 8:42 pm

  6. But as my biologist friend pointed out, colors like red and yellow are used by many animals to warn predators. This points to at least some animals seeing those colors the same or having brains hardwired to perceive these colors as a warning.

    posted by Kieran on 1-29-2010 at 8:43 pm

  7. I like your son’s system, Prism! haha

    posted by Shash on 1-29-2010 at 10:22 pm

  8. this may be stupid but what about white paint and white clothes…

    posted by nicole on 1-30-2010 at 1:08 am

  9. I agree with Kieran – plus consider the rods & cones in our eyes that process the different wavelengths of light – with certain exceptions like color blindness etc. the rods & cones work the same & do the same job exactly in every person, thus what one person perceives as red is the same red that everyone else is seeing. People with certain color blindnesses though may have that where what they learn as “red” looks different to them than the rest of us, but those would be the exceptions & not the norm.

    As an aside I sufffer from what is commonly referred to as red-green color blindness. I remember as a child having a difficult time in school learning the different colors. Today I tell everyone I am color dyslexic so don’t be shocked if I am wearing something that doesn’t exactly match, because it matches to me LOL

    posted by Barn on 1-30-2010 at 7:11 am

  10. That picture you posted is awfully unfaithful to the whole \white\ thing. It’s 90% blue (and 10% yellow)! D:

    Don’t mind me, I’m just an artist >_>

    posted by Ashley on 1-30-2010 at 7:26 am

  11. and for advanced head-twisting: as you can see from the photo above, shadows on snow are often blue

    posted by PartiallyDeflected on 1-30-2010 at 11:31 am

  12. Why is Snow White what? Dopey’s really confused.

    posted by Joe Maz on 1-30-2010 at 7:02 pm

  13. Why is Snow White?
    Because Sleeping Beauty!

    posted by PartiallyDeflected on 1-30-2010 at 8:46 pm

  14. The point about individual perceptions of colour can also be applied to cultural/linguistic differences. In Russian (and probably in some other languages), what we call ‘light blue’ and ‘dark blue’ are two different colours (goluboy and cinii, apologies for the probably faulty transliteration), so to a Russian mind, calling both of those just ‘blue’ would be like if somebody insisted on calling pink and red ‘light red’ and ‘dark red’.

    posted by Gwan on 2-1-2010 at 7:15 am

  15. To get a bit more scientific, this is called Mie scattering. There are basically 2 types of light scatttering, Rayleigh scattering and Mie scattering

    When light hits any particle, a certain amount of scattering occurs. If the partcle is smaller than the waveleongth of the light (i.e. an oxygen molecule) the scattering of the light is wavelenth dependant. This is why the sky appears to be blue, as blue is a shorter wavelength and is scattered more easily by small molecules. This is Rayleigh scattering.

    When the particle is bigger than the wavelength of light, like snow, or the water molecules in clouds and fog, the light scatters more evenly across the spectrum, and what you see is a white diffuse reflection. This is Mie scattering.

    posted by Brad on 2-1-2010 at 12:29 pm

  16. There’s a major oversight (no pun intended) in this article. It presumes that the sun emits all wavelengths in “equal measure”. The sun’s emissions are accurately modeled as a black body (just like an incandescent lightbulb is). This means that the sun emits a particular distribution of light, and certainly not all of it in equal measure.

    We perceive light as “white” when all of our photo receptors are stimulated equally. Since each type of receptor has a different sensitivity, in order to stimulate the receptors to an equal degree there must be an unequal amount of light from each part of the visible spectrum.

    The concept of white light, and how we perceive it is a complex marriage of physics and evolution.

    posted by Austin L on 2-10-2010 at 2:03 pm

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